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The Struts User's Guide - Introduction

1. The configuration bean for this ExceptionHandler object If className specified className must be a org apache struts config ExceptionConfig subclass of the default configuration bean The name of the exception handler extends that this will inherit configuration None information from Fully qualified Java class name for __ this exception handler handler org apache struts action ExceptionHandler The key to use with this handler s message resource bundle that will retrieve the error message template for this exception The module relative URI to the resource that will complete the request response if this exception occurs key None path None The context request or session that is used to access the ActionError scope object request org apache struts action ActionError for this exception Fully qualified Java class name of the type exception type to register with this None handler You can override global exception handlers by defining a handler inside an action definition A common use of ExceptionHandlers is to configure one for java 1lang Exception so it s called for any exception and log the exception to some data store 9 of 15 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html 10 of 15 4 6 Plugin Classes The PlugIn interface extends Action and so that applications can easi
2. bean lt taglib uri gt lt taglib location gt WEB INF struts bean tld lt taglib location gt lt taglib gt lt taglib gt lt taglib uri gt http struts apache org tags html lt taglib uri gt lt taglib location gt WEB INF struts html tld lt taglib location gt lt taglib gt lt taglib gt lt taglib uri gt http struts apache org tags logic lt taglib uri gt lt taglib location gt WEB INF struts logic tld lt taglib location gt lt taglib gt lt taglib gt lt taglib uri gt http struts apache org tags tiles lt taglib uri gt lt taglib location gt WEB INF struts tiles tld lt taglib location gt lt taglib gt lt taglib gt lt taglib uri gt http struts apache org tags nested lt taglib uri gt lt taglib location gt WEB INF struts nested tld lt taglib location gt lt taglib gt This tells the JSP system where to find the tag library descriptor for this library in your application s wEB INF directory instead of out on the Internet somewhere 5 4 3 1 Configure the Struts Tag Libraries Servlet 2 3 2 4 Servlet 2 3 2 4 users only The Servlet 2 3 and 2 4 specifications simplify the deployment and 8 of 11 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html 9 of 11 configuration of tag libraries The instructions above will work on older containers as well as 2 3
3. e The Struts tag library e The JavaServer Pages Standard tag library Once you understand how to use these two consider Struts tag attribute values being evaluated the same way the JSTL tag attribute values are Past that there is very little else you need to know to effectively use the Struts EL tag library Although the Struts EL tag library is a direct port of the tags from the Struts tag library not all of the tags in the Struts tag library were implemented in the Struts EL tag library This was the case if it was clear that the functionality of a particular Struts tag could be entirely fulfilled by a tag in the JSTL It is assumed that developers will want to use the Struts EL tag library along with the JSTL so it is reasonable to assume that they will use tags from the JSTL if they fill their needs For more see Struts El Extension in the FAQ HOWTO section Next Building Controller Components Copyright c 2000 2005 The Apache Software Foundation Powered by Struts 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html 1 of 15 y The Apache Software Foul http www apache truts 4 Building Controller Components 4 1 Overview Now that we understand how to construct the Model and View components of your application it is time to focus on the Controller components Struts includes a servlet that implements the primary function
4. and 2 4 containers Struts only requires a servlet 2 2 container however if you re using a 2 3 2 4 container such as Tomcat 4 x 5 x you can take advantage of a simplified deployment All that s required to install the Struts tag libraries is to copy struts jar into your WEB INF 1ib directory and reference the tags in your code like this lt taglib uri http struts apache org tags html prefix html gt Note that you must use the full uri defined in the various tlds see the example configuration for reference so that the container knows where to find the tag s class files You don t have to alter your web xm1 file or copy tlds into any application directories 5 5 Add Struts Components To Your Application To use Struts you must copy the tld files that you require into your WEB INF directory and copy struts jar and all of the commons jar files into your WEB INF 1ib directory Servlet 2 3 2 4 Users See section 4 5 3 1 for how to avoid copying the tlds into your application Sidebar Sharing JAR Files Across Web Applications Many servlet containers and application servers provide facilities for sharing JAR files across multiple web applications that depend on them For example Tomcat 4 1 allows you to put JAR files into the SCATALINA_HOME shared lib Or CATALINA_HOME common 1ib directories and the classes in those JAR files will be available in all applications without the need to place them in every
5. appropriate ActionForward It is wise to avoid creating lengthy and complex Action classes If you start to embed too much logic in the Action class itself you will begin to find the Act ion class hard to understand maintain and impossible to reuse Rather than creating overly complex Action classes it is generally a good practice to move most of the persistence and business logic to a separate application layer When an Action class becomes lengthy and procedural it may be a good time to refactor your application architecture and move some of this logic to another conceptual layer otherwise you may be left with an inflexible application which can only be accessed in a web application environment Struts should be viewed as simply the foundation for implementing MVC in your applications Struts provides you with a useful control layer but it is not a fully featured platform for building MVC applications soup to nuts The MailReader example application included with Struts stretches this design principle somewhat because the business logic itself is embedded in the Act ion classes This should be considered something of a bug in the design of the example rather than an intrinsic feature of the Struts architecture or an approach to be emulated In order to demonstrate in simple terms the different ways Struts can be used the MailReader application does not always follow best practices 4 5 Exception Handler You can define an Ex
6. base name of the resource bundle for the application In the case described above it would be com mycompany mypackage MyApplication lt servlet gt lt servlet name gt action lt servlet name gt lt servlet class gt org apache struts action ActionServlet lt servlet class gt lt init param gt lt param name gt application lt param name gt lt param value gt com mycompany mypackage MyResources lt param value gt lt init param gt Rls 244 S gt lt servlet gt The important thing is for the resource bundle to be found on the class path for your application Another approach is to store the MyResources properties file in your application s classes folder You can then simply specify myResources as the application value Just be careful it is not deleted if your build script deletes classes as part of a clean target If it does here is an Ant task to run when compiling your application that copies the contents of a src conf directory to the classes directory lt Copy any configuration files gt lt copy todir classes gt lt fileset dir src conf gt lt copy gt 2005 10 10 1 08 The Struts User s Guide Building View Components http struts apache org userGuide building_view htm 3 3 Forms and FormBean Interactions Note While the examples given here use JSP and custom tags the ActionForm beans and the other Struts controller components are View neutral Struts can be
7. can list its properties type and defaults in the Struts configuration file 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html 4 of 15 For example add the following to struts config xml for a UserForm bean that stores a user s given and family names lt form bean name UserForm type org apache struts action DynaActionForm gt lt form property name givenName type Java lang String initial John gt lt form property name familyName type Java lang String initial Smith gt lt form bean gt The types supported by DynaActionForm include e java lang BigDecimal e java lang BigInteger e boolean and java lang Boolean e byte and java lang Byte e char and java lang Character e java lang Class e double and java lang Double float and java lang Float int and java lang Integer long and java lang Long short and java lang Short java lang String e java sql Date e java sql Time e java sql Timestamp You may also specify Arrays of these types e g String You may also specify a concrete implementation of the Map Interface such as java util HashMap or a List implementation such as java util ArrayList If you do not supply an initial attribute numbers will be initialized to 0 and objects to null In JSP pages using the original Struts custom tags attributes of DynaAct ionForm objects can be referenced just like o
8. config file to customize your application See Configuring Applications for more about the other elements in the Struts configuration file The controller uses an internal copy of this document to parse the configuration an Internet 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html connection is not required for operation The outermost XML element must be lt st rut s config gt Inside of the lt struts config gt element there are three important elements that are used to describe your actions e lt form beans gt lt global forwards gt lt action mappings gt lt form beans gt This section contains your form bean definitions Form beans are descriptors that are used to create ActionForm instances at runtime You use a lt form bean gt element for each form bean which has the following important attributes name A unique identifier for this bean which will be used to reference it in corresponding action mappings Usually this is also the name of the request or session attribute under which this form bean will be stored e type The fully qualified Java classname of the ActionForm subclass to use with this form bean lt global forwards gt This section contains your global forward definitions Forwards are instances of the ActionForward class returned from an ActionForm s execute method These map logical names to spec
9. defined above Silently swallowed reserved for future use If not specified the default pagePattern is consistent with the previous behavior of URL calculation S M P optional e processorClass The fully qualified Java class name of the Request Processor subclass to be used with this module org apache struts chain ComposableRequestProcessor optional e tempDir Temporary working directory to use when processing file uploads the directory provided by the servlet container This example uses the default values for several controller parameters If you only want default behavior you can omit the controller section altogether lt controller processorClass org apache struts action RequestProcessor contentType text html gt 5 2 2 Message Resources Configuration Struts has built in support for internationalization I18N You can define one or more lt message resources gt elements for your webapp modules can define their own resource bundles Different bundles can be used simultaneously in your application the key attribute is used to specify the desired bundle e className Classname of configuration bean org apache struts config MessageResourcesConfig optional e factory Classname of MessageResourcesFactory org apache struts util Property MessageResourcesFactory optional e key ServletContext attribute key to store this bundle org apache struts action MESSAGE optional e null Set to
10. e html img generates a HTML lt img gt element with the ability to dynamically modify the URLs specified by the src and lowsrc attributes in the same manner that lt html link gt can e bean parameter retrieves the value of the specified request parameter and defines the result as a page scope attribute of type String or String 3 3 4 Automatic Form Validation In addition to the form and bean interactions described above Struts offers an additional facility to validate the input fields it has received To utilize this feature override the following method in your ActionForm class validate ActionMapping mapping HttpServletRequest request The validate method is called by the controller servlet after the bean properties have been populated but before the corresponding action class s execute method is invoked The validate method has the following options 2005 10 10 1 08 http struts apache org userGuide building_view htm The Struts User s Guide Building View Components http struts apache org userGuide building_view htm 5 of 9 e Perform the appropriate validations and find no problems Return either nu11 ora zero length ActionErrors instance and the controller servlet will proceed to call the perform method of the appropriate Act ion class e Perform the appropriate validations and find problems Return an ActionErrors instance containing ActionError s which are classes that contain the error mess
11. gt lt forward name failure path mainMenu jsp gt lt forward name success path 1 jsp gt lt action gt The in the path attribute allows the mapping to match the request URIs edit Subscription editRegistration or any other URI that starts with edit however editSubscription add would not be matched The part of the URI matched by the wildcard will then be substituted into various attributes of the action mapping and its action forwards replacing 1 For the rest of the request Struts will see the action mapping and its action forwards containing the new values Mappings are matched against the request in the order they appear in the Struts configuration file If more than one pattern matches the last one wins so less specific patterns must appear before more specific ones However if the request URL can be matched against a path without any wildcards in it no wildcard matching is performed and order in not important Wildcard patterns can contain one or more of the following special tokens Matches zero or more characters excluding the slash character 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html 14 of 15 Matches zero or more characters including the slash character The backslash character is used as an escape sequence Thus matches the cnaracter character asterisk and m
12. is required by the application For more about the Struts taglibs and using presentation pages with the framework see the Building View Components chapter Additional documentation regarding the taglibs is also available in the Developer Guides see menu 1 2 3 The Controller ActionServiet and ActionMapping 2 of 5 2005 10 10 1 06 The Struts User s Guide Introduction http struts apache org userGuide introduction html 3 of 5 The Controller portion of the application is focused on receiving requests from the client typically a user running a web browser deciding what business logic function is to be performed and then delegating responsibility for producing the next phase of the user interface to an appropriate View component In Struts the primary component of the Controller is a servlet of class ActionServlet This servlet is configured by defining a set of ActionMappings An ActionMapping defines a path that is matched against the request URI of the incoming request and usually specifies the fully qualified class name of an Action class All Actions are subclassed from org apache struts action Action Actions encapsulate calls to business logic classes interpret the outcome and ultimately dispatch control to the appropriate View component to create the response Struts also supports the ability to use Act ionMapping classes that have additional properties beyond the standard ones required to operate the framework This allo
13. of mapping a request URI to an Action class Therefore your primary responsibilities related to the Controller are e Write an ActionForm class to mediate between the Model and the View See also Building an ActionForm e Write an action class for each logical request that may be received extend org apache struts action Action e Configure a ActionMapping in XML for each logical request that may be submitted The XML configuration file is usually named st ruts config xml To deploy your application you will also need to e Update the web application deployment descriptor file in XML for your application to include the necessary Struts components e Add the appropriate Struts components to your application The latter two items are covered in the Configuring Applications chapter 4 2 The ActionServlet For those of you familiar with MVC architecture the ActionServlet represents the C the controller The job of the controller is to process user requests determine what the user is trying to achieve according to the request e pull data from the model if necessary to be given to the appropriate view and select the proper view to respond to the user The Struts controller delegates most of this grunt work to the Request Processor and Action classes In addition to being the front controller for your application the ActionServlet instance also is responsible for initialization and clean up of resources When
14. org userGuide building_model html 3 of 3 For small scale systems or for state information that need not be kept for a long period of time a set of system state beans may contain all the knowledge that the system ever has of these particular details Or as is often the case the system state beans will represent information that is stored permanently in some external database such as a CustomerBean object that corresponds to a particular row in the CUSTOMERS table and are created or removed from the server s memory as needed Entity Enterprise JavaBeans are also used for this purpose in large scale applications 2 5 Business Logic Beans You should encapsulate the functional logic of your application as method calls on JavaBeans designed for this purpose These methods may be part of the same classes used for the system state beans or they may be in separate classes dedicated to performing the logic In the latter case you will usually need to pass the system state beans to be manipulated to these methods as arguments For maximum code re use business logic beans should be designed and implemented so that they do not know they are being executed in a web application environment If you find yourself having to import a javax servlet class in your bean you are tying this business logic to the web application environment Consider rearranging things so that your Action classes part of the Controller role as described below translate al
15. principle by creating the following tags unique to the implementation of this application e checkLogon Checks for the existence of a particular session object and forwards control to the logon page if it is missing This is used to catch cases where a user has bookmarked a page in the middle of your application and tries to bypass logging on or if the user s session has been timed out Note that there are better ways to authenticate users the checkLogon tag is simply meant to demonstrate writing your own custom tags e linkSubscription Generates a hyperlink to a details page for a Subscription which passes the required primary key values as request attributes This is used when listing the subscriptions associated with a user and providing links to edit or delete them e linkUser Generates a hyperlink to a details page for a User which passes the required primary key values as request attributes The source code for these tags is in the src example directory in package org apache struts example along with the other Java classes that are used in this application 3 4 2 Page Composition With Includes Creating the entire presentation of a page in one JSP file with custom tags and beans to access the required dynamic data is a very common design approach and was employed in the example application included with Struts However many applications require the display of multiple logically distinct portions of your application toget
16. that the statics are global only within a particular web applicaiton which would be true if the class was loaded from the webapp class loader There are many cases where Struts and the Commons libraries it relies on use static variables to maintain information that is presumed to be visible only within a single web applicaiton Sharing these JAR files can cause unwanted interactions and probably cause incorrect behavior e When JAR files are shared like this it is not possible to update the JAR file versions employed by a single web application without updating all of them In addition because updating a Struts version normally requires recompilation of the applications that use it you will have to recompile all of your applications as well instead of being able to manage them independently In spite of these difficulties it is possible that sharing the Struts and Commons JAR files might appear to work for you However this is NOT a supported configuration If you file a bug report for cClassNotFoundException or NoClassDefFoundError exceptions or similar situations where it appears that the wrong version of a class is being loaded the bug report will NOT be processed unless the problem exists with the JAR files in their recommended location in the WEB INF 1ib subdirectory of your webapp 5 6 Logging in Struts Based Applications Since Struts 1 0 the logging functionality was fairly limited You could set a debu
17. the controller initializes it first loads the application config corresponding to the config init param It then goes through an enumeration of all init param elements looking for those elements who s name starts with config For each of these elements Struts loads the configuration file specified by the value of that init param and assigns a prefix value to that module s ModuleConfig instance consisting of the piece of the init param name following config For example the module prefix specified by the init param config foo would be foo This is important to know since this is how the controller determines which module will be given control of processing the request To access the module foo you would use a URL like 2005 10 10 1 08 The Struts User Guide Building Controller Components 2 of 15 http struts apache org userGuide building_controller html http localhost 8080 myApp foo someAction do For each request made of the controller the method process HttpServletRequest HttpServletResponse will be called This method simply determines which module should service the request and then invokes that module s RequestProcessor s process method passing the same request and response 4 2 1 Request Processor The RequestProcessor is where the majority of the core processing occurs for each request Let s take a look at the helper functions the process method invokes in turn rocessPath ke processLocale
18. used by a JSP to collect data from the user by an Action object to validate the user entered data and then by the JSP again to re populate the form fields In the case of validation errors Struts has a shared mechanism for raising and displaying error messages Another element of the Struts Configuration are the ActionFormBeans org apache struts action ActionFormBeans This is a collection of descriptor objects that are used to create instances of the ActionForm objects at runtime When a mapping needs an ActionForm the servlet looks up the form bean descriptor by name and uses it to create an ActionForm instance of the specified type Here is the sequence of events that occur when a request calls for an mapping that uses an ActionForm e The controller servlet either retrieves or creates the ActionForm bean instance e The controller servlet passes the bean to the Action object e If the request is being used to submit an input page the Action object can examine the data If necessary the data can be sent back to the input form along with a list of messages to display on the page Otherwise the data can be passed along to the business tier e If the request is being used to create an input page the Action object can populate the bean with any data that the input page might need The Struts framework includes custom tags that can automatically populate fields from a JavaBean All most JavaServer Pages really need to know about th
19. used with Velocity Templates XSL and any other presentation technology that can be rendered via a Java servlet At one time or another most web developers have built forms using the standard capabilities of HTML such as the lt input gt tag Users have come to expect interactive applications to have certain behaviors and one of these expectations relates to error handling if the user makes an error the application should allow them to fix just what needs to be changed without having to re enter any of the rest of the information on the current page or form Fulfilling this expectation is tedious and cumbersome when coding with standard HTML and JSP pages For example an input element for a username field might look like this in JSP lt input type text name username value lt loginBean getUsername gt gt which is difficult to type correctly confuses HTML developers who are not knowledgeable about programming concepts and can cause problems with HTML editors Instead Struts provides a comprehensive facility for building forms based on the Custom Tag Library facility of JSP 1 1 The case above would be rendered like this using Struts lt html text property username gt with no need to explicitly refer to the JavaBean from which the initial value is retrieved That is handled automatically by the JSP tag using facilities provided by the framework HTML forms are sometimes used to upload other files M
20. want the input attribute of lt act ion gt elements to be the name of a local or global Act ionForward which will then be used to calculate the ultimate URL Set to false to treat the input parameter of lt action gt elements as a module relative path to the resource to be used as the input form false optional e locale Set to true if you want a Locale object stored in the user s session if not already present true optional e maxFileSize The maximum size in bytes of a file to be accepted as a file upload Can be expressed as a number followed by a K M or G which are interpreted to mean kilobytes megabytes or gigabytes respectively 250M optional e multipartClass The fully qualified Java class name of the multipart request handler class to be used with this module org apache struts upload CommonsMultipartRequestHandler optional e nocache Set to true if you want the controller to add HTTP headers for defeating caching to every response from this module false optional e pagePattern Replacement pattern defining how the page attribute of custom tags using it is mapped to a context relative URL of the corresponding resource This value may consist of any combination of the following M Replaced by the module prefix of this module o P Replaced by the path attribute of the selected lt forward gt element o Causes a literal dollar sign to be rendered x Where x is any character not
21. web application s WEB INF 1lib directory Usually the sharing is accomplished by creating a separate class loader that is the parent of the class loader created by your container for each individual web application If you have multiple Struts based web applications it is tempting to consider taking advantage of this container feature and placing struts jar and the various commons jar files in the shared directory rather than in each web application However there are several potential and actual problems with this approach e Classes loaded from the shared class loader cannot see classes in the web application s class loader unless they are specifically programmed to use the Thread context class loader For example Struts dynamically loads your action and form bean classes and normally would not be able to find those classes Struts has been programmed to deal with this in most scenarios but it has not been thoroughly audited to ensure that it works in all scenarios The Commons libraries that Struts uses have NOT been audited to catch all possible scenarios where this might become a problem e When a class is loaded from a shared class loader static variables used within that class become global as well This can cause 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html 10 of 11 inter webapp conflicts when the underlying code assumes
22. 2 Inform the controller of your module 3 Use Actions to refer to your pages 5 3 1 Module Configuration Files Back in Struts 1 0 a few boot strap options were placed in the web xm1 file and the bulk of the configuration was done in a single st rut s config xml file Obviously this wasn t ideal for a team environment since multiple users had to share the same configuration file Since Struts 1 1 you have two options you can list multiple struts config files as a comma delimited list or you can subdivide a larger application into modules With the advent of modules a given module has its own configuration file This means each team each module would presumably be developed by a single team has their own configuration file and there should be a lot less contention when trying to modify it 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html 5 3 2 Informing the Controller Since Struts 1 0 you listed your configuration file as an initialization parameter to the action servlet in web xml This is still done since Struts 1 1 but the parameter can be extended In order to tell the Struts machinery about your different modules you specify multiple config initialization parameters with a slight twist You ll still use config to tell the ActionServlet about your default module however for each additional module you will list an initialization param
23. Act ionForm class itself requires no specific methods to be implemented It is used to identify the role these particular beans play in the overall architecture Typically an ActionForm bean will have only property getter and property setter methods with no business logic e The ActionForm object also offers a standard validation mechanism If you override a stub method and provide error messages in the standard application resource Struts will automatically validate the input from the form using your method See Automatic Form Validation for details Of course you can also ignore the ActionForm validation and provide your own in the Action object e Define a property with associated get xxx and set xxx methods for each field that is present in the form The field name and property name must match according to the usual JavaBeans conventions see the Javadoc for the java beans Introspector Class for a start on information about this For example an input field named username will cause the setUsername method to be called e Buttons and other controls on your form can also be defined as properties This can help determine which button or control was selected when the form was submitted Remember the ActionForm is meant to represent your data entry form not just the data beans e Think of your ActionForm beans as a firewall between HTTP and the Action Use the validate method to ensure all required properties are present and that they con
24. Text Some applications require dynamically generated text or markup such as XML If a complete page is being rendered and can be output using a PrintWriter this is very easy to do from an Action response setContentType text plain or text xml PrintWriter writer response getWriter use writer to render text return null 3 4 6 The Struts EL Tag Library The Struts EL tag library is a contributed library in the Struts distribution It represents an integration of the Struts tag library with the JavaServer Pages Standard Tag Library or at least the expression evaluation engine that is used by the JSTL The base Struts tag library contains tags which rely on the evaluation of rtexprvalue s runtime scriptlet expressions to evaluate dynamic attribute values For instance to print a message from a properties file based on a resource key you would use the bean write tag perhaps like this lt bean message key lt stringvar gt gt This assumes that st ringvar exists as a JSP scripting variable If you re using the Struts EL library the reference looks very similar but slightly different like this 2005 10 10 1 08 The Struts User s Guide Building View Components http struts apache org userGuide building_view htm 9 of 9 lt bean el message key stringvar gt If you want to know how to properly use the Struts EL tag library there are two important things you need to know
25. The Struts User s Guide Introduction http struts apache org userGuide introduction html ia Paste Software Fol g http www apach tr 1 Introduction 1 1 Forward into the Past or a brief history of Struts When Java servlets were first invented many programmers quickly realized that they were a Good Thing They were faster and more powerful that standard CGI portable and infinitely extensible But writing HTML to send to the browser in endless printin statements was tiresome and problematic The answer to that was JavaServer Pages which turned Servlet writing inside out Now developers could easily mix HTML with Java code and have all the advantages of servlets The sky was the limit Java web applications quickly became JSP centric This in and of itself was not a Bad Thing but it did little to resolve flow control issues and other problems endemic to web applications Another model was clearly needed Many clever developers realized that JavaServer Pages AND servlets could be used together to deploy web applications The servlets could help with the control flow and the JSPs could focus on the nasty business of writing HTML In due course using JSPs and servlets together became known as Model 2 meaning presumably that using JSPs alone was Model 1 Of course there is nothing new under the Sun and many have been quick to point out that JSP s Model 2 follows the classic Model View Controller
26. age keys into the application s MessageResources bundle that should be displayed The controller servlet will store this array as a request attribute suitable for use by the lt html errors gt tag and will forward control back to the input form identified by the input property for this ActionMapping As mentioned earlier this feature is entirely optional The default implementation of the validate method returns null and the controller servlet will assume that any required validation is done by the action class One common approach is to perform simple prima facia validations using the ActionForm validate method and then handle the business logic validation from the Action The Struts Validator covered in the next section may be used to easily validate ActionForms 3 3 5 The Struts Validator Configuring the Validator to perform form validation is easy 1 The ActionForm bean must extend ValidatorForm 2 The form s JSP must include the lt html javascript gt tag for client side validation 3 You must define the validation rules in an xml file like this lt form validation gt lt formset gt lt form name logonForm gt lt field property username depends required gt lt msg name required key error username gt lt field gt lt form gt lt formset gt lt form validation gt The msg element points to the message resource key to use when generating the error message 4 Lastly you m
27. alidation if requested on the ActionForm associated with this request if any If this mapping represents a forward forward to the path specified by the mapping If this mapping represents an include include the result of invoking the path in this request Instantiate an instance of the class specified by the current ActionMapping if necessary This is the point at which your action s perform or execute method will be called Finally the process method of the RequestProcessor takes the ActionForward returned by your Action class and uses to select the next resource if any Most often the ActionForward leads to the presentation page that renders the response 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html 3 of 15 4 3 ActionForm Classes An ActionForm represents an HTML form that the user interacts with over one or more pages You will provide properties to hold the state of the form with getters and setters to access them ActionForms can be stored in either the session default or request scopes If they re in the session it s important to implement the form s reset method to initialize the form before each use Struts sets the ActionForm s properties from the request parameters and sends the validated form to the appropriate Action s execute method When you code your Act ionForm beans keep the following principles in mind e The
28. and the available operations might be embedded within the Action classes that are part of the Struts control layer This can be useful when the logic is very simple or where reuse of the business logic in other environments is not contemplated The Struts framework architecture is flexible enough to support most any approach to accessing the Model but we strongly recommend that you separate the business logic how it s done from the role that Act ion classes play what to do nuff said For more about adapting your application s Model to Struts see the Building Model Components chapter 1 2 2 The View JSP Pages and Presentation Components The View portion of a Struts based application is most often constructed using JavaServer Pages JSP technology JSP pages can contain static HTML or XML text called template text plus the ability to insert dynamic content based on the interpretation at page request time of special action tags The JSP environment includes a set of standard action tags such as lt jsp useBean gt whose purpose is described in the JavaServer Pages Specification In addition to the built in actions there is a standard facility to define your own tags which are organized into custom tag libraries Struts includes a set of custom tag libraries that facilitate creating user interfaces that are fully internationalized and interact gracefully with Act ionForm beans ActionForms capture and validate whatever input
29. assword input fields radio buttons reset buttons select lists with embedded option or options items option options submit buttons text input fields textareas In every case a field tag must be nested within a form tag so that the field knows what bean to use for initializing displayed values 3 3 3 Other Useful Presentation Tags There are several tags useful for creating presentations consult the documentation on each specific tag library along with the Tag Developers Guides for more information e logic iterate repeats its tag body once for each element of a specified collection which can be an Enumeration a Hashtable a Vector or an array of objects e logic present depending on which attribute is specified this tag checks the current request and evaluates the nested body content of this tag only if the specified value is present Only one of the attributes may be used in one occurrence of this tag unless you use the property attribute in which case the name attribute is also required The attributes include cookie header name parameter property role scope and user e logic notPresent the companion tag to present notPresent provides the same functionality when the specified attribute is not present e html link generates a HTML lt a gt element as an anchor definition or a hyperlink to the specified URL and automatically applies URL encoding to maintain session state in the absence of cookie support
30. atches the character backslash In the action mapping and action forwards the wildcard matched values can be accessed with the token N where n is a number from 1 to 9 indicating which wildcard matched value to substitute The whole request URI can be accessed with the 0 token The action mapping attributes that will accept wildcard matched strings are type name roles parameter attribute forward include e input Also the action mapping properties set using the lt set property key foo value bar gt syntax will accept wildcard matched strings in their value attribute The action forward attributes that will accept wildcard matched strings are path 4 11 Commons Logging Interface Struts doesn t configure logging itself it s all done by commons logging under the covers The default algorithm is a search e If Log4J is there use it e If JDK 1 4 is there use it e Otherwise use SimpleLog The commons logging interface is an ultra thin bridge to many different logging implementations The intent is to remove compile and run time dependencies on any single logging implementation For more information about the currently supported implementations please refer to the the description for the org apache commons logging package Because Struts uses commons logging and therefore includes the necessary JAR files for you to use commons logging you ve probably had the occasi
31. based system can be often be divided into two major subsystems the internal state of the system and the actions that can be taken to change that state In grammatical terms we might think about state information as nouns things and actions as verbs changes to the state of those things Many applications represent the internal state of the system as a set of one or more JavaBeans The bean properties represent the details of the system state Depending on your application s complexity these beans may be self contained and know how to persist their own state or they may be facades that know how to retrieve the system s state from another component This component may be a database a search engine an Entity Enterprise JavaBean a LDAP server or something else entirely Large scale applications will often represent the set of possible business operations as methods that can be called on the bean or beans maintaining the state information For example you might have a shopping cart bean stored in session scope for each current user with properties that represent the current set of items that the user has decided to purchase This bean might also have a checkout method that authorizes the user s credit card and sends the order to the warehouse to be picked and shipped Other systems will represent the available operations separately perhaps as Session Enterprise JavaBeans Session EJBs In a smaller scale application on the other h
32. ceptionHandler to execute when an Action s execute method throws an Exception First you need to subclass org apache struts action ExceptionHandler and override the execute method Your execute method should process the Exception and return an ActionForward object to tell Struts where to forward to next Then you configure your handler in struts config xml like this lt global exceptions gt lt exception 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html key some key type Java io IOException handler com yourcorp ExceptionHandler gt lt global exceptions gt This configuration element says that com yourcorp ExceptionHandler execute will be called when any IOException is thrown by an Action The key is a key into your message resources properties file that can be used to retrieve an error message If the handler attribute is not specified the default handler stores the exception in the request attribute under the value of the Globals EXCEPTION_KEY global key The possible attributes for the exception element are as follows Attribute Description Default Servlet context attribute for the message resources bundle associated with this handler The default bundle fA s sie org apache struts Globals MESSAGES_KEY attribute is the value specified by the string constant declared at Globals MESSAGES_KEY
33. classes would also need to be modified Of course you can define whatever local forward properties makes sense for your own application The Struts configuration file includes several other elements that you can use to customize your application See Configuring Applications for details 4 9 Using ActionMappings for Pages Fronting your pages with ActionMappings is essential when using modules since doing so is the only way you involve the controller in the request and you want to The controller puts the application configuration in the request which makes available all of your module specific configuration data including which message resources you are using request processor and so forth The simplest way to do this is to use the forward property of the ActionMapping lt action path view forward view jsp gt 4 10 Using Wildcards in ActionMappings Since Struts 1 2 0 As a Struts application grows in size so will the number of action mappings Wildcards can be used to combine similiar mappings into one more generic mapping The best way to explain wildcards is to show an example and walk through how it works This example modifies the previous mapping in the ActionMapping Example section to use wildcards to match all pages that start with edit lt Generic edit mapping gt lt action path edit type org apache struts webapp example Edit l Action name 1 Form scope request validate false
34. cumentation bundle for your JDK release for more information e PropertyResourceBundle One of the standard implementations of ResourceBundl allows you to define resources using the same name value syntax used to initialize properties files This is very convenient for preparing resource bundles with messages that are used in a web application because these messages are generally text oriented MessageFormat The java text MessageFormat Class allows you to replace portions of a message string in this case one retrieved from a resource bundle with arguments specified at run time This is useful in cases where you are creating a sentence but the words would appear in a different order in different languages The placeholder string 0 in the message is replaced by the first runtime argument 1 is replaced by the second argument and so on e MessageResources The Struts class org apache struts util MessageResources lets you treat a set of resource bundles like a database and allows you to request a particular message string for a particular Locale normally one associated with the current user instead of for the default Locale the server itself is running in 2005 10 10 1 08 The Struts User s Guide Building View Components http struts apache org userGuide building_view htm 2 of 9 Please note that the i18n support in a framework like Struts is limited to the presentation of internationalized text and image
35. d on the MailReader example application The MailReader application now uses DynaActionForms But in this example we ll show a conventinal ActionForm instead to illustrate the usual workflow Note that the entries for all the other actions 11 of 15 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html are left out lt struts config gt lt form beans gt lt form bean name logonForm type org apache struts webapp example LogonForm gt lt form beans gt lt global forwards type org apache struts action ActionForward gt lt forward name logon path logon jsp redirect false gt lt global forwards gt lt action mappings gt lt action path logon type org apache struts webapp example LogonAction name logonForm scope request input logon jsp unknown false validate true gt lt action mappings gt lt struts config gt First the form bean is defined A basic bean of class org apache struts webapp exampl LogonForm is mapped to the logical name logonForm This name is used as a request attribute name for the form bean The global forwards section is used to create logical name mappings for commonly used presentation pages Each of these forwards is available through a call to your action mapping instance i e mapping findForward logicalName As you can see this mapping matches
36. design pattern abstracted from the venerable Smalltalk MVC framework Java Web developers now tend to use the terms Model 2 and MVC interchangeably In this guide we use the MVC paradigm to describe the Struts architecture which might be best termed a Model 2 MVC design The Struts project was launched in May 2000 by Craig R McClanahan to provide a standard MVC framework to the Java community In July 2001 Struts 1 0 was released and IOHO Java Model 2 development will never be quite the same 1 2 The Model View Controller MVC Design Pattern In the MVC design pattern application flow is mediated by a central Controller The Controller delegates requests in our case HTTP requests to an appropriate handler The handlers are tied to a Model and each handler acts as an adapter between the request and the Model The Model represents or encapsulates an application s business logic or state Control is usually then forwarded back through the Controller to the appropriate View The forwarding can be determined by consulting a set of mappings usually loaded from a database or configuration file This provides a loose coupling between the View and Model which can make applications significantly easier to create and maintain 1 2 1 The Model System State and Business Logic JavaBeans 1 of 5 2005 10 10 1 06 The Struts User s Guide Introduction http struts apache org userGuide introduction html The Model portion of an MVC
37. e rest of the framework is 4 of 5 2005 10 10 1 06 The Struts User s Guide Introduction http struts apache org userGuide introduction html the field names to use and where to submit the form Other Struts tags can automatically output messages queued by an Action or ActionForm and simply need to be integrated into the page s markup The messages are designed for localization and will render the best available message for a user s locale The Struts framework and its custom tag libraries were designed from the ground up to support the internationalization features built into the Java platform All the field labels and messages can be retrieved from a message resource To provide messages for another language simply add another file to the resource bundle Internationalism aside other benefits to the message resources approach are consistent labeling between forms and the ability to review all labels and messages from a central location For the simplest applications an Action object may sometimes handle the business logic associated with a request However in most cases an Action object should invoke another object usually a JavaBean to perform the actual business logic This lets the Action focus on error handling and control flow rather than business logic To allow reuse on other platforms business logic JavaBeans should not refer to any Web application objects The Action object should translate needed details from the HTTP r
38. each class individually However it would be a burden to be required to maintain such settings for every possible class so the logging environment supports the notion of logging hierarchies as well If a detail level configuration for a particular class has not been set the logging system looks up the hierarchy until it finds a configuration setting to use or else uses the default detail level if no configuration for any level of the hierarchy has been 2005 10 10 1 09 The Struts User s Guide Configuring Applications 11 of 11 http struts apache org userGuide configuration html explicitly set In the case of our messages from RequestProcessor the logging system will look for explicit settings of the following loggers in this order until it finds one e Q K Q apache apache apache apache struts action RequestProcessor struts action Struts The default logging detail level for your log implementation In a similar manner the detail level for messages from PropertyUtils from the Commons BeanUtils library is set by a search for configuration settings for org org apache apache apache apache commons beanutil ls PropertyUtils commons beanutil commons S The default logging detail level for your log implementation You can seamlessly integrate logging from your own components into the same logging implementation that Struts and the Commons libraries
39. ements is loaded Since Struts 1 1 e validating Should we use a validating XML parser to process the configuration file strongly recommended true e configFactory The Java class name of the ModuleConfigFactory used to create the implementation of the ModuleConfig interface org apache struts config impl DefaultModuleConfigFactory e chainConfig Comma separated list of either context relative or classloader path s to load commons chain catalog definitions from If none specified the default Struts catalog that is provided with Struts will be used Since Struts 1 3 WARNING Struts will not operate correctly if you define more than one lt servlet gt element for a controller servlet or a subclass of the standard controller servlet class The controller servlet MUST be a web application wide singleton 6 of 11 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html 7 of 11 5 4 2 Configure the ActionServiet Mapping Note The material in this section is not specific to Struts The configuration of servlet mappings is defined in the Java Servlet Specification This section describes the most common means of configuring a Struts application There are two common approaches to defining the URLs that will be processed by the controller servlet prefix matching and extension matching An appropriate mapping entry for each approach will be described below P
40. enerated dynamically at request time Since the properties of these forms ActionForm beans are not all known ahead of time we need a new approach Struts allows you to make one or more of your ActionForm s properties values a Map instead of a traditional atomic object You can then store the data from your form s dynamic fields in that Map Here is an example of a map backed ActionForm class public FooForm extends ActionForm private final Map values new HashMap public void setValue String key Object value values put key value public Object getValue String key return values get key In its corresponding JSP page you can access objects stored in the values map using a special notation mapname keyname The parentheses in the bean property name indicate that 5 of 15 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html e The bean property named mapname is indexed using Strings probably backed by a Map and that e Struts should look for get set methods that take a String key parameter to find the correct sub property value Struts will of course use the keyname value from the parentheses when it calls the get set methods Here is a simple example lt html text property value foo gt This will call the get Value method on FooForm with a key value of foo to find the property value To create a form with dynamic f
41. equest and pass those along to the business logic beans as regular Java variables In a database application for example A business logic bean will connect to and query the database The business logic bean returns the result to the Action The Action stores the result in a form bean in the request The JavaServer Page displays the result in a HTML form Neither the Action nor the JSP need to know or care from where the result comes They just need to know how to package and display it Other chapters in this document cover the various Struts components in greater detail The Struts release also includes several Developer Guides covering various aspects of the frameworks along with sample applications the standard Javadoc API and of course the complete source code Struts is distributed under the Apache Software Foundation license The code is copyrighted but is free to use in any application Next Building Model Components Copyright c 2000 2005 The Apache Software Foundation Powered by Struts 5 of 5 2005 10 10 1 06 The Struts User s Guide Building Model Components http struts apache org userGuide building_model html ie Paste Software Fol g http www apach tr 2 Building Model Components 2 1 Overview Many requirements documents used for building web applications focus on the View However you should ensure that the processing required for each submitted request is also clearly de
42. er Among other things that means you can conditionally perform the include by nesting it within a tag like equal by using it s parameter attribute e The bean include tag takes either a an argument forward representing a logical name mapped to the jsp to include or the id argument which represents a page context String variable to print out to the jsp page 3 4 3 Page Composition With Tiles Tiles is a powerful templating library that allows you to construct views by combining various tiles Here s a quick setup guide 1 Create a layout layout jsp file that contains your app s common look and feel lt html gt lt body gt lt tiles insert attribute body gt lt body gt lt html gt 2 Create your index jsp homepage file lt hl gt This is my homepage lt h1 gt 3 Create a WEB INF tiles defs xml file that looks like this lt tiles definitions gt lt definition name layout path layout layout jsp gt lt put name body value gt lt definition gt lt definition name homepage extends layout gt lt put name body value index jsp gt lt definition gt lt tiles definitions gt 4 Setup the TilesPlugin in the struts config xml file lt plug in className org apache struts tiles TilesPlugin gt lt set property property definitions config value WEB INF tiles defs xml gt lt plug in gt 5 Setup an action mapping in struts config xml to point to your
43. eter named config module where module is the prefix for your module this gets used when determining which URIs fall under a given module so choose something meaningful For example lt init param gt lt param name gt config lt param name gt lt param value gt WEB INF conf struts default xml lt param value gt lt init param gt lt init param gt lt param name gt config modulel lt param name gt lt param value gt WEB INF conf struts modulel xml lt param value gt lt init param gt Here we have two modules One happens to be the default module identified by the param name of config and the other will be using the module prefix module1 based on the param name it was given config module1 The controller is configured to find the respective configuration files under wzEB INF conf which is the recommended place to put all configuration files Pretty simple The st ruts default xml would be equivalent to what most folks call strut s config xml I just like the symmetry of having all my Struts module configuration files being named struts module xml If you d like to vary where the pages for each module are stored see the forwardPattern setting for the Controller 5 3 3 Switching Modules There are three approaches for switching from one module to another You can use the built in org apache struts actions SwitchAction you can use a lt forward gt global or local and
44. false to display missing resource keys in your application like 2 of 11 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html 3 of 11 keyname instead of nu11 true optional e parameter Name of the resource bundle required Example configuration lt message resources parameter MyWebAppResources null false gt This would set up a message resource bundle provided in the file MyWebAppResources properties under the default key Missing resource keys would be displayed as keyname 5 2 3 Plugin Configuration Struts PlugIns are configured using the lt plug in gt element within the Struts configuration file This element has only one valid attribute className which is the fully qualified name of the Java class which implements the org apache struts action PlugIn interface For PlugIns that require configuration themselves the nested lt set property gt element is available This is an example using the Tiles plugin lt plug in className org apache struts tiles TilesPlugin gt lt set property property definitions config value WEB INF tiles defs xml gt lt plug in gt 5 3 Configuring your application for modules Very little is required in order to start taking advantage of the Struts module feature Just go through the following steps 1 Prepare a configuration file for each module
45. fined from the Model s perspective In general the developer of the Model components will be focusing on the creation of JavaBeans classes that support all of the functional requirements The precise nature of the beans required by a particular application will vary widely depending on those requirements but they can generally be classified into several categories discussed below However a brief review of the concept of scope as it relates to beans and JSP is useful first 2 2 JavaBeans and Scope Within a web based application JavaBeans can be stored in and accessed from a number of different collections of attributes Each collection has different rules for the lifetime of that collection and the visibility of the beans stored there Together the rules defining lifetime and visibility are called the scope of those beans The JavaServer Pages JSP Specification defines scope choices using the following terms with the equivalent servlet API concept defined in parentheses e page Beans that are visible within a single JSP page for the lifetime of the current request Local variables of the service method e request Beans that are visible within a single JSP page as well as to any page or servlet that is included in this page or forwarded to by this page Request attributes e session Beans that are visible to all JSP pages and servlets that participate in a particular user session across one or more requests Session attrib
46. g xml in order to allow different modules in the same web application to be configured differently For full details on available parameters see the struts config_1_2 dtd or the list below e bufferSize The size in bytes of the input buffer used when processing file uploads 4096 optional e className Classname of configuration bean org apache struts config ControllerConfig optional e contentType Default content type and optional character encoding to be set on each response May be overridden by the Action JSP or other resource to which the request is forwarded text html optional e forwardPattern Replacement pattern defining how the path attribute of a lt forward gt element is mapped to a context relative URL when it starts with a slash and when the contextRelative property is false This value may consist of any combination of the following o M Replaced by the module prefix of this module o P Replaced by the path attribute of the selected lt forward gt element o Causes a literal dollar sign to be rendered o x Where x is any character not defined above Silently swallowed reserved for future use 1 of 11 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html If not specified the default forwardPattern is consistent with the previous behavior of forwards M P optional e inputForward Set to true if you
47. gging detail level with a servlet initialization parameter and all log messages were written to wherever ServletContext 1log output is sent by your servlet container With Struts 1 1 however all logging messages written by Struts itself as well as the commons libraries that it utilizes flow through an abstract wrapper called Commons Logging which can be used as a wrapper around any logging implementation The most common implementations used are simple logging to System err the Apache Log4J package or the built in logging capabilities of JDK 1 4 or later in the java util logging package This section does not attempt to fully explain how Commons Logging is configured and used Instead it focuses on pertinent details of using Commons Logging in a Struts based environment For complete documentation on using Commons Logging consult the documentation for the logging system you are using plus the Commons Logging Javadocs Commons Logging provides fine grained control over the logging messages created by a Log instance By convention the Log instances for Struts and the Commons packages in general are named the fully qualified class name of the class whose messages are being logged Therefore log messages created by the Request Processor Class are naturally enough directed toa logger named org apache struts action RequestProcessor The advantage of this approach is that you can configure the level of detail in the output you want from
48. her on a single page For example a portal application might have some or all of the following functional capabilities available on the portal s home page e Access to a search engine for this portal e One or more news feed displays with the topics of interest customizedfrom the user s registration profile Access to discussion topics related to this portal A mail waiting indicator if your portal provides free email accounts The development of the various segments of this site is easier if you can divide up the work and assign different developers to the different segments Then you can use the include capability of JavaServer Pages technology to combine the results into a single result page or use the include tag provided with Struts There are three types of include available depending on when you w ant the combination of output to occur e An lt include file xxxxx gt directive can include a file that contains Java code 2005 10 10 1 08 The Struts User s Guide Building View Components http struts apache org userGuide building_view htm or JSP tags The code in the included file can even reference variables declared earlier in the outer jsp page The code is inlined into the other JavaServer Page before it is compiled so it can definitely contain more than just HTML e The include action lt jsp include page xxxxx flush true gt is processed at request time and is handled transparently by the serv
49. homepage tile lt action path index 7 of 9 2005 10 10 1 08 The Struts User s Guide Building View Components http struts apache org userGuide building_view htm 8 of 9 type org apache struts actions ForwardAction parameter homepage gt The TilesPlugin configures a special RequestProcessor that determines if the requested view is a tile and processes it accordingly Note that we made the homepage tile extend our root layout tile and changed the body attribute Tiles inserts the file named in the body attribute into the main layout See the tiles documentation webapp for in depth examples 3 4 4 Image Rendering Components Some applications require dynamically generated images like the price charts on a stock reporting site Two different approaches are commonly used to meet these requirements e Render a hyperlink with a URL that executes a servlet request The servlet will use a graphics library to render the graphical image set the content type appropriately such as to image gif and send back the bytes of that image to the browser which will display them just as if it had received a static file e Render the HTML code necessary to download a Java applet that creates the required graph You can configure the graph by setting appropriate initialization parameters for the applet in the rendered code or you can have the applet make its own connection to the server to receive these parameters 3 4 5 Rendering
50. ield names you could do the following for int i 0 i lt 10 i String name value foo i 4 mye oe Vv lt html text property lt name gt gt lt br gt A ale oe Vv Note that there is nothing special about the name value Your map backed property could instead be named property thingy or any other bean property name you prefer You can even have multiple map backed properties on the same bean In addition to map backed properties you can also create list backed properties You do so by creating indexed get set methods on your bean public FooForm extends ActionForm private final List values new ArrayList public void setValue int key Object value values set key value public Object getValue int key return values get key In your presentation pages you access individual entries in a list backed property by using a different special notation 1istname index The braces in the bean property name indicate that the bean property named 1istname is indexed probably backed by a List and that Struts should look for get set methods that take an index parameter in order to find the correct sub property value While map backed ActionForms provide you with more flexibility they do not support the same range of syntax available to conventional or DynaActionForms You might have difficulty referencing indexed or mapped properties using a map backed ActionForm The
51. ific resources typically JSPs allowing you to change the resource without changing references to it throughout your application You use a lt forward gt element for each forward definition which has the following important attributes e name The logical name for this forward This is used in your ActionForm s execute method to forward to the next appropriate resource Example homepage e path The context relative path to the resource Example index jsp or index do redirect True or false default Should the ActionServlet redirect to the resource instead of forward lt action mappings gt This section contains your action definitions You use an lt action gt element for each of the mappings you would like to define Most action elements will define at least the following attributes e path The application context relative path to the action e type The fully qualified java classname of your Action class name The name of your lt form bean gt element to use with this action Other often used attributes include e parameter A general purpose attribute often used by standard Actions to pass a required property e roles A comma delimited list of the user security roles that can access this mapping For a complete description of the elements that can be used with the action element see the Struts Configuration DTD and the ActionMapping documentation 4 8 1 ActionMapping Example Here s a mapping entry base
52. l other topics related to the View components are briefly discussed 3 2 Internationalized Messages A few years ago application developers could count on having to support only residents of their own country who are used to only one or sometimes two languages and one way to represent numeric quantities like dates numbers and monetary values However the explosion of application development based on web technologies as well as the deployment of such applications on the Internet and other broadly accessible networks have rendered national boundaries invisible in many cases This has translated if you will pardon the pun into a need for applications to support internationalization often called i18n because 18 is the number of letters in between the i and the n and localization Struts builds upon the standard classes available on the Java platform to build internationalized and localized applications The key concepts to become familiar with are e Locale The fundamental Java class that supports internationalization is Locale Each Locale represents a particular choice of country and language plus an optional language variant and also a set of formatting assumptions for things like numbers and dates e ResourceBundle The java util ResourceBundle class provides the fundamental tools for supporting messages in multiple languages See the Javadocs for the ResourceBundle Class and the information on Internationalization in the do
53. l required information from the HTTP request being processed into property setter calls on your business logic beans after which a call to an execute method can be made Such a business logic class can be reused in environments other than the web application for which they were initially constructed Depending on the complexity and scope of your application business logic beans might be ordinary JavaBeans that interact with system state beans passed as arguments or ordinary JavaBeans that access a database using JDBC calls For larger applications these beans will often be stateful or stateless Enterprise JavaBeans EJBs instead For more about using a database with your application see the Accessing a Database HowTo Next Building View Components Copyright c 2000 2005 The Apache Software Foundation Powered by Struts 2005 10 10 1 07 The Struts User s Guide Building View Components http struts apache org userGuide building_view htm 1 of 9 The Apache Software Foli http www apach truts 3 Building View Components 3 1 Overview This chapter focuses on the task of building the View components for use with the Struts framework Many applications rely on JavaServer Pages JSP technology to create the presentation layer The Struts distribution includes a comprehensive JSP tag library that provides support for building internationalized applications as well as for interacting with input forms Severa
54. ller servlet and so have access to that servlet s methods When forwarding control an Action object can indirectly forward one or more shared objects including JavaBeans by placing them in one of the standard contexts shared by Java Servlets For example an Action object can create a shopping cart bean add an item to the cart place the bean in the session context and then forward control to another mapping That mapping may use a JavaServer Page to display the contents of the user s cart Since each client has their own session they will each also have their own shopping cart In a Struts application most of the business logic can be represented using JavaBeans An Action can call the properties of a JavaBean without knowing how it actually works This encapsulates the business logic so that the Action can focus on error handling and where to forward control JavaBeans can also be used to manage input forms A key problem in designing Web applications is retaining and validating what a user has entered between requests With Struts you can define your own set of input bean classes by subclassing ActionForm org apache struts action ActionForm The ActionForm class makes it easy to store and validate the data for your application s input forms The ActionForm bean is automatically saved in one of the standard shared context collections so that it can be used by other objects like an Action object or another JSP The form bean can be
55. ly hook into the ActionServlet lifecycle This interface defines two methods init and destroy which are called at application startup and shutdown respectively A common use of a Plugin Action is to configure or load application specific data as the web application is starting up At runtime any resource setup by init would be accessed by Actions or business tier classes The PlugIn interface allows you to setup resources but does not provide any special way to access them Most often the resource would be stored in application context under a known key where other components can find it PlugIns are configured using lt plug in gt elements within the Struts configuration file See PlugIn Configuration for details 4 7 The ActionMapping Implementation In order to operate successfully the Struts controller servlet needs to know several things about how each request URI should be mapped to an appropriate Act ion class The required knowledge has been encapsulated in a Java class named ActionMapping the most important properties are as follows type Fully qualified Java class name of the Action implementation class used by this mapping name The name of the form bean defined in the config file that this action will use e path The request URI path that is matched to select this mapping See below for examples of how matching works and how to use wildcards to match multiple request URIs e unknown Set to true if thi
56. ngle Act ionForm bean that contains properties for all of the fields no matter which page the field is actually displayed on Likewise the various pages of the same form should all be submitted to the same Action Class If you follow these suggestions the page designers can rearrange the fields among the various pages often without requiring changes to the processing logic Smaller applications may only need a single ActionForm to service all of its input forms Others applications might use a single ActionForm for each major subsystem of the application Some teams might prefer to have a separate ActionForm class for each distinct input form or workflow How many or how few ActionForms to use is entirely up to you The framework doesn t care 2 4 System State Beans The actual state of a system is normally represented as a set of one or more JavaBeans classes whose properties define the current state A shopping cart system for example will include a bean that represents the cart being maintained for each individual shopper and will among other things include the set of items that the shopper has currently selected for purchase Separately the system will also include different beans for the user s profile information including their credit card and ship to addresses as well as the catalog of available items and their current inventory levels 2005 10 10 1 07 The Struts User s Guide Building Model Components http struts apache
57. on classes in the Struts MailReader example application Next Configuring Applications Copyright c 2000 2005 The Apache Software Foundation Powered by Struts 15 of 15 2005 10 10 1 08 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html ia Paste Software Fol g http www apach tr yur Us S 5 Configuring Applications 5 1 Overview Before you can build an application you need to lay a solid foundation There are several setup tasks you need to perform before deploying your Struts application These include components in the Struts configuration file and in the Web Application Deployment Descriptor 5 2 The Struts configuration file The Building Controller Components chapter covered writing the lt form bean gt and lt action mapping gt portions of the Struts configuration file These elements usually play an important role in the development of a Struts application The other elements in Struts configuration file tend to be static you set them once and leave them alone These static configuration elements are e lt controller gt e lt message resources gt e lt plug in gt 5 2 1 Controller Configuration The lt controller gt element allows you to configure the ActionServlet Many of the controller parameters were previously defined by servlet initialization parameters in your web xml file but have been moved to this section of strut s confi
58. onal fleeting thought Should I use commons logging The answer surprise depends on the requirements for your particular project If one of your requirements is the ability to easily change logging implementations with zero impact on your application then commons logging is a very good option Great What do I do to get started using commons logging in my own code Using commons logging in your own code is very simple all you need are two imports and a declaration for a logger Let s take a look package com foo import org apache commons logging Log import org apache commons logging LogFactory public class Foo 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html bh Geet private static Log log LogFactory getLog Foo class public void setBar Bar bar if log isTraceEnabled log trace Setting bar to bar this bar bar The general idea is to instantiate a single logger per class and to use a name for the logger which reflects where it s being used The example is constructed with the class itself This gives the logger the name of com foo Foo Doing things this way lets you easily see where the output is coming from so you can quickly pin point problem areas In addition you are able to enable disable logging in a very fine grained way For examples of using logging in Struts classes see the Acti
59. ost browsers support this through a lt input type file gt element that generates a file browse button but it s up to the developer to handle the incoming files Struts handles these multipart forms in a way identical to building normal forms For an example of using Struts to create a simple login form see the Buiding an ActionForm Howto 3 3 1 Indexed amp Mapped Properties Property references in JSP pages using the Struts framework can reference Java Bean properties as described in the JavaBeans specification Most of these references refer to scalar bean properties referring to primitive or single Object properties However Struts along with the Jakarta Commons Beanutils library allow you to use property references which refer to individual items in an array collection or map which are represented by bean methods using well defined naming and signature schemes Documentation on the Beanutils package can be found at http jakarta apache org commons beanutils api index html More information about using indexed and mapped properties in Struts can be found in the FAQ describing Indexed Properties Mapped Properties and Indexed Tags 3 3 2 Input Field Types Supported 2005 10 10 1 08 The Struts User s Guide Building View Components 4 of 9 Struts defines HTML tags for all of the following types of input fields with hyperlinks to the corresponding reference information checkboxes hidden fields p
60. p through how this all fits together When initialized the controller parses a configuration file st rut s config xm1 and uses it to deploy other control layer objects Together these objects form the Struts Configuration The Struts Configuration defines among other things the ActionMappings org apache struts action ActionMappings for an application The Struts controller servlet consults the ActionMappings as it routes HTTP requests to other components in the framework Requests may be forwarded to JavaServer Pages or Action org apache struts action Action subclasses provided by the Struts developer Often a request is first forwarded to an Action and then to a JSP or other presentation page The mappings help the controller turn HTTP requests into application actions An individual ActionMapping org apache struts action ActionMapping will usually contain a number of properties including e arequest path or URI 2005 10 10 1 06 The Struts User s Guide Introduction http struts apache org userGuide introduction html e the object type Action subclass to act upon the request and e other properties as needed The Action object can handle the request and respond to the client usually a Web browser or indicate that control should be forwarded elsewhere For example if a login succeeds a login action may wish to forward the request onto the mainMenu page Action objects have access to the application s contro
61. parameters supported by the action servlet are described below You can also find these details in the Javadocs for the ActionServlet class Square brackets describe the default values that are assumed if you do not provide a value for that initialization parameter e config Context relative path to the XML resource containing the configuration information for the default module This may also be a comma delimited list of configuration files Each file is loaded in turn and its objects are appended to the internal data structure WEB INF struts config xml WARNING If you define an object of the same name in more than one configuration file the last one loaded quietly wins e config module Context relative path to the XML resource containing the configuration information for the application module that will use the specified prefix module This can be repeated as many times as required for multiple application modules Since Struts 1 1 e convertNull Force simulation of the Struts 1 0 behavior when populating forms If set to true the numeric Java wrapper class types like java lang Integer will default to null rather than 0 Since Struts 1 1 false e rulesets Comma delimited list of fully qualified classnames of additional org apache commons digester RuleSet instances that should be added to the Digester that will be processing struts config xml files By default only the Ruleset for the standard configuration el
62. rdinary Act ionForm objects Wherever a Struts tag refers to a property the tags will automatically use the DynaActionForm properties just like those of a conventional JavaBean You can even expose DynaActionForm properties using bean define Although you can t use bean define to instantiate a DynaActionForm since it needs to be setup with the appropriate dyna properties If you are using the Struts JSTL EL taglib the references are different however Only properties of ordinary Act ionForm objects can be directly accessed through the JSTL expression language syntax The DynaAct ionForm properties must be accessed through a slightly different syntax The JSTL EL syntax for referencing a property of an Act ionForm goes like this S formbean prop The syntax for referencing a property of a DynaAct ionForm would be S dynabean map prop 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html The map property is a property of DynaAct ionForm which represents the HashMap containing the DynaAct ionForm properties DynaActionForms are meant as an easy solution to a common problem Your ActionForms use simple properties and standard validations and you just pass these properties over to another JavaBean say using BeanUtils copyProperties myBusinessBean form DynaActionForms are not a drop in replacement for ActionForms If you need to access ActionForm p
63. refix matching means that you want all URLs that start after the context path part with a particular value to be passed to this servlet Such an entry might look like this lt servlet mapping gt lt servlet name gt action lt servlet name gt lt url pattern gt do lt url pattern gt lt servlet mapping gt which means that a request URI to match the 1ogon path described earlier might look like this http www mycompany com myapplication do logon where myapplication is the context path under which your application is deployed Extension mapping on the other hand matches request URIs to the action servlet based on the fact that the URI ends with a period followed by a defined set of characters For example the JSP processing servlet is mapped to the jsp pattern so that it is called to process every JSP page that is requested To use the do extension which implies do something the mapping entry would look like this lt servlet mapping gt lt servlet name gt action lt servlet name gt lt url pattern gt do lt url pattern gt lt servlet mapping gt and a request URI to match the 1ogon path described earlier might look like this http www mycompany com myapplication logon do WARNING Struts will not operate correctly if you define more than one lt servlet mapping gt element for the controller servlet WARNING If you are using the new module support since Struts 1 1 you should be aware
64. rocessContent gej rocessNoCache processPreprocess processMapping processRoles processActionForm rocessPopulate processValidate rocessForward ge rocessInclude ko processActionCreate rocessActionPerform T processForwardConfig Determine the path that invoked us This will be used later to retrieve an ActionMapping Select a locale for this request if one hasn t already been selected and place it in the request Set the default content type with optional character encoding for all responses if requested If appropriate set the following response headers Pragma Cache Control and Expires This is one of the hooks the RequestProcessor makes available for subclasses to override The default implementation simply returns true If you subclass RequestProcessor and override processPreprocess you should either return true indicating process should continue processing the request or false indicating you have handled the request and the process should return Determine the ActionMapping associated with this path If the mapping has a role associated with it ensure the requesting user has the specified role If they do not raise an error and stop processing of the request Instantiate if necessary the ActionForm associated with this mapping if any and place it into the appropriate scope Populate the ActionForm associated with this request if any Perform v
65. roperties in your Action you will need to use the map style accessor like myForm get name If you actively use the ActionForm object in your Action then you may want to use conventional ActionForms instead DynaActionForms cannot be instantiated using a no argument constructor In order to simulate the extra properties there is a lot of machinery involved in their construction You must rely on Struts to instantiate a DynaActionForm for you via the ActionMapping If need be you can extend the DynaActionForm to add custom validate and reset methods you might need Simply specify your subclass in the struts config instead However you cannot mix conventional properties and DynaProperties A conventional getter or setter on a DynaActionForm won t be found by the reflection utilities To use DynaActionForms with the Struts Validator specify org apache struts validator ValidatorActionForm or your subclass as the form bean class And of course while the DynaActionForm may support various binary types properties used with the html text tag should still be String properties DynaActionForms relieve developers of maintaining simple ActionForms For even less maintenance try Niall Pemberton s Lazy ActionForm 4 3 2 Map backed ActionForms The DynaActionForm classes offer the ability to create ActionForm beans at initialization time based on a list of properties enumerated in the Struts configuration file However many HTML forms are g
66. ruts configuration file see Building the Controller Components the Struts controller servlet will automatically perform the following services for you before invoking the appropriate Act ion method e Check for an instance of a bean of the appropriate class under the appropriate key in the appropriate scope request or session e If there is no such bean instance available a new one is automatically created and added to the appropriate scope request or session e For every request parameter whose name corresponds to the name of a property in the bean the corresponding setter method will be called This operates in a manner similar to the standard JSP action lt jsp setProperty gt when you use the asterisk wildcard to select all properties e The updated Act ionForm bean will be passed to the execute method of an Action class org apache struts Action so that the values can be made available to your system state and business logic beans For more about coding Actions and Act ionForm beans see the Building Controller Components chapter You should note that a form in the sense discussed here does not necessarily correspond to a single JSP page in the user interface It is common in many applications to have a form from the user s perspective that extends over multiple pages Think for example of the wizard style user interface that is commonly used when installing new applications Struts encourages you to define a si
67. s action should be configured as the default for this application to handle all requests not handled by another action Only one action can be defined as a default within a single application validate Set to true if the validate method of the action associated with this mapping should be called e forward The request URI path to which control is passed when this mapping is invoked This is an alternative to declaring a type property 4 8 Writing Action Mappings How does the controller servlet learn about the mappings you want It would be possible but tedious to write a small Java class that simply instantiated new Act ionMapping instances and called all of the appropriate setter methods To make this process easier Struts uses the Jakarta Commons Digester component to parse an XML based description of the desired mappings and create the appropriate objects initialized to the appropriate default values See the Jakarta Commons website for more information about the Digester The developer s responsibility is to create an XML file named st rut s config xmi and place it in the WEB INF directory of your application This format of this document is described by the Document Type Definition DTD maintained at http struts apache org dtds struts config_1_2 dtd This chapter covers the configuration elements that you will typically write as part of developing your application There are several other elements that can be placed in the struts
68. s to the user Support for Locale specific input methods used with languages such as Japanese Chinese and Korean is left up to the client device whichis usually a web browser For an internationalized application follow the steps described in the Internationalization document in the JDK documentation bundle for your platform to create a properties file containing the messages for each language An example will illustrate this further Assume that your source code is created in package com mycompany mypackage So it is stored in a directory relative to your source directory named com mycompany mypackage To create a resource bundle called com mycompany mypackage MyApplication you would create the following files in the com mycompany mypackage directory e MyApplication properties Contains the messages in the default language for your server If your default language is English you might have an entry like this prompt hello Hello e MyApplication_xx properties Contains the same messages in the language whose ISO language code is xx See the ResourceBundle Javadoc page for a link to the current list For a French version of the message shown above you would have this entry prompt hello Bonjour You can have resource bundle files for as many languages as you need When you configure the controller servlet in the web application deployment descriptor one of the things you will need to define in an initialization parameter is the
69. specify the contextRelative attribute with a value of true or you can specify the module parameter as part of any of the Struts hyperlink tags Include Img Link Rewrite or Forward You can use org apache struts actions SwitchAction like so lt action mappings gt lt action path toModule type org apache struts actions SwitchAction gt lt action mappings gt Now to change to ModuleB we would use a URI like this http localhost 8080 toModule do prefix moduleB amp page index do 4 of 11 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html If you are using the default module as well as named modules like moduleB you can switch back to the default module with a URI like this http localhost 8080 toModule do prefix amp page index do Here s an example of a global forward lt global forwards gt lt forward name toModuleB contextRelative true path moduleB index do redirect true gt lt global forwards gt You could do the same thing with a local forward declared in an ActionMapping lt action mappings gt lt action lt forward name success contextRelative true path moduleB index do redirect true gt lt action gt lt action mappings gt Or you can use org apache struts actions SwitchAction lt action mappings gt lt action path toModule type org apache s
70. ssigned by your JVM to each request thread so there is no need to worry about sharing them An Act ion can be factored into several local methods so long as all variables needed are passed as method parameters This assures thread safety as the JVM handles such variables internally using the call stack which is associated with a single Thread Conserve Resources As a general rule allocating scarce resources and keeping them across requests from the same user in the user s session can cause scalability problems For example if your application uses JDBC and you allocate a separate JDBC connection for every user you are probably going to run in some scalability issues when your site suddenly shows up on Slashdot You should strive to use pools and release resources such as database connections prior to forwarding control to the appropriate View component even if a bean method you have called throws an exception e Don t throw it catch it Ever used a commercial website only to have a stack trace or exception thrown in your face after you ve already typed in your credit card number and clicked the purchase button Let s just say it doesn t inspire confidence Now is your chance to deal with these application errors in the Act ion class If your application specific code throws expections you should catch these exceptions in your Action class log them in your application s log servlet log Error message exception and return the
71. tain reasonable values An ActionForm that fails validation will not even be presented to the Action for handling e You may also place a bean instance on your form and use nested property references For example you might have a customer bean on your ActionForm and then refer to the property customer name in your presentation page This would correspond to the methods customer getName and customer setName string Name on your customer bean See the Tag Library Developer Guides for more about using nested syntax with the Struts JSP tags e Caution If you nest an existing bean instance on your form think about the properties it exposes Any public property on an ActionForm that accepts a single String value can be set with a query string It may be useful to place beans that can affect the business state inside a thin wrapper that exposes only the properties required This wrapper can also provide a filter to be sure runtime properties are not set to inappropriate values 4 3 1 DynaActionForm Classes Maintaining a separate concrete ActionForm class for each form in your Struts application is time consuming It is particularly frustrating when all the ActionForm does is gather and validate simple properties that are passed along to a business JavaBean This bottleneck can be alleviated through the use of DynaActionForm classes Instead of creating anew ActionForm subclass and new get set methods for each of your bean s properties you
72. that no logon exists the request can be forwarded to the presentation page that displays the username and password prompts for logging on This could occur because a user tried to enter an application in the middle say from a bookmark or because the session has timed out and the servlet container created a new one e If validation is not complete validate the form bean properties as needed If a problem is found store the appropriate error message keys as a request attribute and forward control back to the input form so that the errors can be corrected e Perform the processing required to deal with this request such as saving a row into a database This can be done by logic code embedded within the Action class itself but should generally be performed by calling an appropriate method of a business logic bean e Update the server side objects that will be used to create the next page of the user interface typically request scope or session scope beans depending on how long you need to keep these items available e Return an appropriate Act ionForward object that identifies the presentation page to be used to generate this response based on the newly updated beans Typically you will acquire a reference to such an object by calling findForward on either the Act ionMapping object you received if you are using a logical name local to this mapping or on the controller servlet itself if you are using a logical name global to the applica
73. that only extension mapping is supported 5 4 3 Configure the Struts Tag Libraries Next you must add an entry defining the Struts tag libraries The struts bean taglib contains tags useful in accessing beans and their properties as well as defining new beans based on these accesses that are accessible to the remainder of the page via scripting variables and page scope attributes Convenient mechanisms to create new beans based on the value of request cookies headers and parameters are also provided 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html The struts html taglib contains tags used to create Struts input forms as well as other tags generally useful in the creation of HTML based user interfaces The struts logic taglib contains tags that are useful in managing conditional generation of output text looping over object collections for repetitive generation of output text and application flow management The struts tiles taglib contains tags used for combining various view components called tiles into a final composite view The struts nested taglib is an extension of other struts taglibs that allows the use of nested beans Below is how you would define all Struts taglibs for use within your application In practice you would only specify the taglibs that your application uses lt taglib gt lt taglib uri gt http struts apache org tags
74. the path 1ogon actually because the MailReader example application uses extension mapping the request URI you specify in a JSP page would end in logon do When a request that matches this path is received an instance of the LogonAction class will be created the first time only and used The controller servlet will look for a bean in request scope under key logonForm creating and saving a bean of the specified class if needed Optional but very useful are the local forward elements In the MailReader example application many actions include a local success and or failure forward as part of an action mapping lt Edit mail subscription gt lt action path editSubscription type org apache struts webapp example EditSubscriptionAction name SubscriptionForm scope request validate false gt lt forward name failure path mainMenu jsp gt lt forward name Success path subscription jsp gt lt action gt Using just these two extra properties the Action classes are almost totally independent of the actual names of the presentation pages The pages can be renamed for example during a redesign with negligible impact on the Action classes themselves If the names of the next 12 of 15 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html 13 of 15 pages were hard coded into the Action classes all of these
75. tion In Struts 1 0 Actions called a perform method instead of the now preferred execute method These methods use the same parameters and differ only in which exceptions they throw The elder perform method throws SerlvetException and IOException The new execute method simply throws Exception The change was to facilitate the Declarative Exception handling feature introduced in Struts 1 1 The perform method may still be used in Struts 1 1 but is deprecated The Struts 1 1 method simply calls the new execute method and wraps any Exception thrown as a ServletException 4 4 1 Action Class Design Guidelines Remember the following design guidelines when coding Act ion classes e Write code for a multi threaded environment The controller servlet creates only one 7 of 15 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html 8 of 15 instance of your Action class and uses this one instance to service all requests Thus you need to write thread safe Act ion classes Follow the same guidelines you would use to write thread safe Servlets Here are two general guidelines that will help you write scalable thread safe Action classes gt Only Use Local Variables The most important principle that aids in thread safe coding is to use only local variables not instance variables in your Act ion class Local variables are created on a stack that is a
76. truts actions SwitchAction gt lt action mappings gt Now to change to ModuleB we would use a URI like this http localhost 8080 toModule do prefix moduleB amp page index do Using the module parameter with a hyperlink tag is even simpler lt html link module moduleB path index do gt That s all there is to it Happy module switching 5 4 The Web Application Deployment Descriptor The final step in setting up the application is to configure the application deployment descriptor stored in file WEB INF web xm1 to include all the Struts components that are required Using the deployment descriptor for the example application as a guide we see that the following 5 of 11 2005 10 10 1 09 The Struts User s Guide Configuring Applications http struts apache org userGuide configuration html entries need to be created or modified 5 4 1 Configure the ActionServliet Instance Add an entry defining the action servlet itself along with the appropriate initialization parameters Such an entry might look like this lt servlet gt lt servlet name gt action lt servlet name gt lt servlet class gt org apache struts action ActionServlet lt servlet class gt lt init param gt lt param name gt config lt param name gt lt param value gt WEB INF struts config xml lt param value gt lt init param gt lt load on startup gt 1 lt load on startup gt lt servlet gt The initialization
77. use by following the instructions in Section 4 10 If you do this you are strongly encouraged to follow the same naming convention for loggers based on the class name of the messages being logged for maximum configuration flexibility For more about putting it all together see the Building Applications HowTo Next Release Notes Copyright c 2000 2005 The Apache Software Foundation Powered by Struts 2005 10 10 1 09
78. ust enable the ValidatorPlugin in the struts config xml file like this lt plug in className org apache struts validator ValidatorPlugiIn gt lt set property property pathnames value WEB INF validator rules xml WEB INF validation xml gt lt plug in gt Note If your required form property is one of the Java object representations of primitive types ie java lang Integer you must set the ActionServlet s convertNull init parameter to true Failing to do this will result in the required validation not being performed on that field because it will default to 0 For more about the Struts Validator see the Developers Guide 2005 10 10 1 08 The Struts User s Guide Building View Components http struts apache org userGuide building_view htm 6 of 9 3 4 Other Presentation Techniques Although the look and feel of your application can be completely constructed based on the standard capabilities of JSP and the Struts custom tag library you should consider employing other techniques that will improve component reuse reduce maintenance efforts and or reduce errors Several options are discussed in the following sections 3 4 1 Application Specific Custom Tags Beyond using the custom tags provided by the Struts library it is easy to create tags that are specific to the application you are building to assist in creating the user interface The MailReader example application included with Struts illustrates this
79. utes e application Beans that are visible to all JSP pages and servlets that are part of a web application Servlet context attributes It is important to remember that JSP pages and servlets in the same web application share the same sets of bean collections For example a bean stored as a request attribute in a servlet like this MyCart mycart new MyCart request setAttribute cart mycart is immediately visible to a JSP page which this servlet forwards to using a standard action tag like this lt jsp useBean id cart scope request class com mycompany MyApp MyCart gt 2 3 ActionForm Beans 1 of 3 2005 10 10 1 07 The Struts User s Guide Building Model Components http struts apache org userGuide building_model html 2 of 3 Note While ActionForm beans often have properties that correspond to properties in your Model beans the form beans themselves should be considered a Controller component As such they are able to transfer data between the Model and View layers The Struts framework generally assumes that you have defined an Act ionForm bean that is a Java class extending the ActionForm class for the input forms in your application ActionForm beans are sometimes just called form beans These may be finely grained objects so that there is one bean for each form or coarsely grained so that one bean serves several forms or even an entire application If you declare such beans in your St
80. validwhen validator since Struts 1 2 1 also does not support map backed ActionForms 4 4 Action Classes The Action class defines two methods that could be executed depending on your servlet environment 6 of 15 2005 10 10 1 08 The Struts User Guide Building Controller Components http struts apache org userGuide building_controller html public ActionForward execute ActionMapping mapping ActionForm form ServletRequest request ServletResponse response throws Exception public ActionForward execute ActionMapping mapping ActionForm form HttpServletRequest request HttpServletResponse response throws Exception Since the majority of Struts projects are focused on building web applications most projects will only use the HttpServletRequest version A non HTTP execute method has been provided for applications that are not specifically geared towards the HTTP protocol The goal of an Action class is to process a request via its execute method and return an ActionForward object that identifies where control should be forwarded e g a JSP Tile definition Velocity template or another Action to provide the appropriate response In the MVC Model 2 design pattern a typical Action class will often implement logic like the following in its execute method e Validate the current state of the user s session for example checking that the user has successfully logged on If the Act ion class finds
81. ws you to store additional information specific to your application and still utilize the remaining features of the framework In addition Struts lets you define logical names to which control should be forwarded so that an action method can ask for the Main Menu page for example without knowing the location of the corresponding JSP page These features greatly assist you in separating the control logic what to do with the view logic how it s rendered For more about the Struts control layer see the Building Controller Components chapter 1 3 Struts Control Flow The Struts framework provides several components that make up the Control layer of a MVC style application These include a controller servlet developer defined request handlers and several supporting objects The Struts custom tag libraries provide direct support for the View layer of a MVC application Some of these access the control layer objects Others are generic tags found convenient when writing applications Other taglibs including JSTL can also be used with Struts Other presentation technologies like Velocity Templates and XSLT can also be used with Struts The Model layer in a MVC application is often project specific Struts is designed to make it easy to access the business end of your application but leaves that part of the programming to other products like JDBC Enterprise Java Beans Object Relational Bridge or Simper to name a few Let s ste

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