Introduction to the Struts Web Framework

This document takes you through the basics of using NetBeans IDE to develop web applications using the Struts web framework. Struts is an open source framework that extends the Java Servlet API and employs a Model, View, Controller (MVC) architecture. It enables you to create maintainable, extensible, and flexible web applications based on standard technologies, such as JSP pages, JavaBeans, resource bundles, and XML.

This tutorial teaches you how to build a simple MVC application that displays a login page and returns a success page upon submitting data that passes validation. You learn several basic features provided by Struts, as well as how these features are implemented using the IDE. Specifically, you use Struts tags in JSP pages, maintain user data with a Struts ActionForm bean, and implement forwarding logic using a Struts Action object. You are also shown how to implement simple validation to your application, including setting up warning message for a failed login attempt.

For a more fine-grained introduction to Struts, see How does Struts work? on the official Struts website. Also, make use of the IDE's Javadoc Index Search (Help > Javadoc Index Search) to view the Struts Framework API, which is packaged with the Struts libraries.

Note: If you are looking for Struts 2 framework support in NetBeans IDE, you should consider installing the NetBeans Struts 2 support plugin.

Contents

• Overview of the Application
• Setting Up a Struts Application
• Creating JSP Pages
  • Creating a Login Page
  • Creating a Success Page
• Creating an ActionForm Bean
• Creating an Action Class
• Implementing Validation
  • Accessing Bean Data and Preparing a Forwarding Condition
  • Setting Up an Error Message
• Adding forward Entries to struts-config.xml
• Building and Running the Application
• See Also

To follow this tutorial, you need the following software and resources.

Notes:

• The Web and Java EE installation enables you to optionally install the GlassFish V2 application server and the Apache Tomcat servlet container 6.0.x. You must install one of these (or register a different server in the IDE) to work through this tutorial.
• If you need to compare your project with a working solution, you can download the sample application.

Overview of the Application

When you use Struts, the framework provides you with a controller servlet, ActionServlet, which is defined in the Struts libraries that are included in the IDE, and which is automatically registered in the web.xml deployment descriptor as shown below. The controller servlet uses a struts-config.xml file to map incoming requests to Struts Action objects, and instantiate any ActionForm objects associated with the action to temporarily store form data. The Action object processes requests using its execute method, while making use of any data stored in the form bean. Once the Action object processes a request, it stores any new data (i.e., in the form bean, or in a separate result bean), and forwards the results to the appropriate view.

Developing a Struts application is similar to developing any other kind of web application in NetBeans IDE. However, you complement your web development toolkit by taking advantage of the Struts support provided by the IDE. For example, you use templates in the IDE to create Struts Action objects and ActionForm beans. Upon creation, the IDE automatically registers these classes in the struts-config.xml file and lets you extend this file very easily using menu items in the Source Editor's right-click menu. Because many web applications use JSP pages for the view, Struts also provides custom tag libraries which facilitate interaction with HTML forms. Within the IDE's Source Editor, you can invoke code completion and Javadoc support that helps you to work efficiently with these libraries.

The following steps demonstrate how to create a simple form that collects user data, performs simple validation, and outputs the data on a success page.

Setting Up a Struts Application

In the IDE, a Struts application is nothing more than a normal web application accompanied by the Struts libraries and configuration files. You create a Struts application in the same way as you create any other web application in the IDE - using the New Web Application wizard, with the additional step of indicating that you want the Struts libraries and configuration files to be included in your application.

1. Choose File > New Project. Under Categories, select Web. Under Projects, select Web Application and click Next.
2. In the Name and Location panel, enter MyStrutsApp for Project Name and click Next.
3. In the Server and Settings panel, select the server to which you want to deploy your application. Only servers that are registered with the IDE are listed. (To register a server, click Add next to the Server drop-down list.) Also, note that the Context Path to your deployed application becomes /MyStrutsApp. Click Next.
4. In the Frameworks panel, select Struts:
   
   For purposes of this tutorial, do not change any of the configuration values in the lower region of this panel. These are the following:
   • Action Servlet Name: The name of the Struts action servlet used in the application. The web.xml deployment descriptor contains an entry for the action servlet and specifies the appropriate Struts-specific parameters, such as the path to the servlet class within the Struts library and to the struts-config.xml configuration file within the application.
   • Action URL Pattern: Specifies the patterns of incoming requests which are mapped to the Struts action controller. This generates a mapping entry in the deployment descriptor. By default, only the *.do pattern is mapped.
   • Application Resource: Lets you specify the resource bundle which will be used in the struts-config.xml file for localizing messages. By default, this is com.myapp.struts.ApplicationResource.
   • Add Struts TLDs: Lets you generate tag library descriptors for the Struts tag libraries. A tag library descriptor is an XML document which contains additional information about the entire tag library as well as each individual tag. In general this is not necessary, because you can refer to on-line URIs rather than local TLD files.
5. Click Finish. The IDE creates the project folder in your file system. As with any web application in the IDE, the project folder contains all of your sources and the IDE's project metadata, such as the Ant build script. However, your web application in addition has all of the Struts libraries on its classpath. Not only are they on the application's classpath, but they are included in the project and will be packaged with it later when you build the project.

The project opens in the IDE. You can view its logical structure in the Projects window and its file structure in the Files window. For example, in the Projects window note that your project appears as follows:

The Struts-specific configuration files, as well as the application's deployment descriptor, are conveniently placed within the Configuration Files folder. Open the deployment descriptor (double-click the web.xml file node to have it display in the Source Editor). In order to handle Struts processing, a mapping is provided for the Struts controller servlet:

<servlet>
    <servlet-name>action</servlet-name>
    <servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
    <init-param>
        <param-name>config</param-name>
        <param-value>/WEB-INF/struts-config.xml</param-value>
    </init-param>
    <init-param>
        <param-name>debug</param-name>
        <param-value>2</param-value>
    </init-param>
    <init-param>
       <param-name>detail</param-name>
       <param-value>2</param-value>
    </init-param>
    <load-on-startup>2</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>action</servlet-name>
    <url-pattern>*.do</url-pattern>
</servlet-mapping>

Above, the Struts controller servlet is named action and is defined in the Struts library (org.apache.struts.action.ActionServlet). It is set to handle all requests that satisfy the *.do mapping. In addition, initialization parameters for the servlet are specified by means of the struts-config.xml file, also contained in the WEB-INF folder.

Creating JSP Pages

Begin by creating two JSP pages for the application. The first displays a form. The second is the view returned when login is successful.

• Creating a Login Page
• Creating a Success Page

Creating an ActionForm Bean

A Struts ActionForm bean is used to persist data between requests. For example, if a user submits a form, the data is temporarily stored in the form bean so that it can either be redisplayed in the form page (if the data is in an invalid format or if login fails) or displayed in a login success page (if data passes validation).

1. Right-click the MyStrutsApp project node and choose New > Other. Under Categories choose Struts, then under File Types choose Struts ActionForm Bean. Click Next.
2. Type in LoginForm for the Class Name. Then select com.myapp.struts in the Package drop-down list and click Finish.
   
   The IDE creates the ActionForm bean and opens it in the Source Editor. By default, the IDE provides it with a String called name and an int called number. Both fields have accessor methods defined for them. Also, the IDE adds a bean declaration to the struts-config.xml file. If you open the struts-config.xml file in the Source Editor, you can see the following declaration, which was added by the wizard:

   <form-beans>
       <form-bean name="LoginForm" type="com.myapp.struts.LoginForm" />
   </form-beans>
   

   The IDE provides navigation support in the struts-config.xml file. Hold down the Ctrl key (⌘ key on Mac) and hover your mouse over the ActionForm bean's fully qualified class name. The name becomes a link, enabling you to navigate directly to the class in the Source Editor:
   
3. In the ActionForm bean in the Source Editor, create fields and accompanying accessor methods that correspond to the name and email text input fields that you created in login.jsp. Because name has already been created in the ActionForm skeleton, you only need to implement email.
   
   Add the following declaration beneath name (changes in bold):

   private String name;
   private String email;
   

   To create accessor methods, place your cursor on email and press Alt-Insert (Ctrl-I on Mac).
   
   Select Getter and Setter, then in the dialog that displays, select email : String and click Generate. Accessor methods are generated for the email field.

   Note: You can delete the declaration and accessor methods for number, as it is not used in this tutorial.

Creating an Action Class

The Action class contains the business logic in the application. When form data is received, it is the execute method of an Action object that processes the data and determines which view to forward the processed data to. Because the Action class is integral to the Struts framework, NetBeans IDE provides you with a wizard.

1. In the Projects window, right-click the MyStrutsApp project node and choose New > Other. From the Struts category choose Struts Action and click Next.
2. In the Name and Location panel, change the name to LoginAction.
3. Select com.myapp.struts in the Package drop-down list.
4. Type /login in Action Path. This value must match the value you set for the action attribute of the <html:form> tags in login.jsp. Make sure settings appear as in the screenshot below, then click Next.
   
5. In the third step of the wizard, you are given the opportunity to associate the Action class with a form bean. Notice that the LoginForm bean you previously created is listed as an option for ActionForm Bean Name. Make the following adjustments to the panel:
   • Delete the forward slash for the Input Resource field
   • Set Scope to Request (Session is the default scope setting in Struts.)
   • Deselect the Validate ActionForm Bean option
   Click Finish. The LoginAction class is generated, and the file opens in the Source Editor. Also note that the following action entry is added to the struts-config.xml file:

   <action-mappings>
       <action name="LoginForm"
           path="/login"
           scope="request"
           type="com.myapp.struts.LoginAction"/>
           validate="false"
       ...
   

   The name and scope attributes apply to the form bean that is associated with the action. Specifically, when an incoming request matches /login, the Struts framework automatically instantiates a LoginForm object and populates it with the form data sent in the request. The default value of validate is set to true. This tells the framework to call the validate method of the form bean. You deselected this option in the wizard however because you will hand-code simple validation in the next step, which does not require the validate method.

Implementing Validation

In the Source Editor, browse through the LoginAction class and look at the execute method:

public ActionForward execute(ActionMapping mapping, ActionForm form,
    HttpServletRequest request, HttpServletResponse response)
    throws Exception {

    return mapping.findForward(SUCCESS);}

Notice the definition of SUCCESS, listed beneath the LoginAction class declaration:

private final static String SUCCESS = "success";

Currently, the mapping.findForward method is set to unconditionally forward any request to an output view called success. This is not really desirable; you want to first perform some sort of validation on the incoming data to determine whether to send the success view, or any different view.

• Accessing Bean Data and Preparing a Forwarding Condition
• Setting Up an Error Message

public class LoginAction extends org.apache.struts.action.Action {

    private final static String SUCCESS = "success";
    private final static String FAILURE = "failure";

    public ActionForward execute(ActionMapping mapping, ActionForm form,
            HttpServletRequest request, HttpServletResponse response)
            throws Exception {

        // extract user data
        LoginForm formBean = (LoginForm)form;
        String name = formBean.getName();
        String email = formBean.getEmail();

        // perform validation
        if ((name == null) ||               // name is empty
             email == null ||               // email is empty
             email.indexOf("@") == -1) {    // email lacks '@'

            formBean.setError();
            return mapping.findForward(FAILURE);
        }

        return mapping.findForward(SUCCESS);

    }
}

Adding forward Entries to struts-config.xml

In order for the application to match JSP pages with forwarding conditions returned by LoginAction's execute method, you need to add forward entries to the struts-config.xml file.

1. Open struts-config.xml in the Source Editor, right-click anywhere in the action entry for LoginForm, and choose Struts > Add Forward. The Add Forward dialog box opens. Type success in Forward Name. Enter the path to success.jsp in the Resource File field. The dialog box should now look as follows:
   
   Click Add. Note that the following forward entry was added to struts-config.xml (changes in bold):

   <action name="LoginForm"
       path="/login"
       scope="request"
       type="com.myapp.struts.LoginAction">
       <forward name="success" path="/WEB-INF/success.jsp"/>
   </action>
   

2. Perform the same action to add a forward entry for failure. Set the path to /login.jsp. The following forward entry is added to struts-config.xml (changes in bold):

   <forward name="success" path="/WEB-INF/success.jsp"/>
   <forward name="failure" path="/login.jsp"/>
   

Building and Running the Struts Application

The IDE uses an Ant build script to build and run your web application. The IDE generated the build script when you created the project, basing it on the options you entered in the New Project wizard. Before you build and run the application, you need to set the application's default entry point to login.jsp.

1. In the Projects window, double-click the web.xml deployment descriptor. The tabs listed along the top of the Source Editor provide you with an interface to the web.xml file. Click on the Pages tab. In the Welcome Files field, enter login.jsp.
   
   Now click on the XML tab to view the file. Note that login.jsp is now listed in the welcome-file entry:

   <welcome-file>login.jsp</welcome-file>
   

2. In the Projects window, right-click the project node and choose Run. The IDE builds the web application and deploys it, using the server you specified when creating the project. The browser opens and displays the loginForm.jsp page. Type in some data that should fail validation, i.e., either leave either field blank, or enter an email address with a missing '@' sign:
   
   When you click Login, the login form page redisplays, containing an error message:
   
   Try entering data that should pass validation. Upon clicking Login, you are presented with the success page:
   

See Also

This concludes the Introduction to the Struts Framework in NetBeans IDE. This document demonstrated how to construct a simple web MVC application in NetBeans IDE using the Struts Framework, and introduced you to the IDE's interface for developing web applications. You were shown how to use Struts tags in JSP pages, temporarily store user data in a Struts ActionForm bean, and implement forwarding logic using a Struts Action object. You are also shown how to implement simple validation to your application, including setting up warning message for a failed login attempt.

For related tutorials, see the following resources:

• Adding Support for a Web Framework. A general guide describing how to add web framework support to NetBeans IDE using the Plugin Manager.
• Introduction to the Spring Web Framework. Describes the basics of using NetBeans IDE to develop web applications using the Spring framework.
• Introduction to the JavaServer Faces Framework. The first of a three-part tutorial demonstrating how to create a simple web application using the JavaServer Faces framework.