Introduction to Spring Web MVC

This document shows you how to construct a simple web MVC application using the Spring Framework. The application enables a user to enter her name in a text field, and upon clicking OK, the name is returned and displayed on a second page with a welcome greeting.

The Spring Framework is a popular open source application framework that can make Java EE development easier. It consists of a container, a framework for managing components, and a set of snap-in services for web user interfaces, transactions, and persistence. A part of the Spring Framework is Spring Web MVC, an extensible MVC framework for creating web applications.

The IDE provides built-in support for Spring Framework 3.0 and 2.5. Framework libraries are packaged with the IDE and are automatically added to the project classpath when the framework is selected. Configuration settings are provided, such as naming and mapping of the Spring Web MVCDispatcherServlet. The JSTL library can optionally be registered upon project creation. Support for Spring XML bean configuration files is also provided, including the following functionality:

• Code completion. Invoked in Spring XML configuration files for Java classes as well as bean references.
• Navigation. Hyperlinking of Java classes and properties mentioned in Spring bean definitions, as well as hyperlinking to other Spring bean references.
• Refactoring. Renaming of references to Java classes in Spring XML configuration files.

For more information on the Spring Framework, visit http://www.springsource.org/. For a more fine-grained explanation of how Spring Framework artifacts behave and interact with other objects in an application, see the official Spring Framework Reference Documentation, or consult the Spring Framework API documentation.

Contents

• Setting up a New Project with Spring Web MVC Support
  • Creating a Spring Web MVC Skeleton Project
  • Running the Skeleton Project
• Overview of the Application
• Implementing a Service
• Implementing the Controller and Model
• Implementing the Views
• See Also

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

Notes:

• The Java installation of the IDE enables you to optionally install and register the GlassFish server with the IDE.
• If you need to compare your project with a working solution, you can download the sample application.

Setting up a New Project with Spring Web MVC Support

• Creating a Spring Web MVC Skeleton Project
• Running the Skeleton Project

<welcome-file-list>
    <welcome-file>redirect.jsp</welcome-file>
</welcome-file-list>

<% response.sendRedirect("index.htm"); %>

<servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>2</load-on-startup>
</servlet>

<servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>*.htm</url-pattern>
</servlet-mapping>

<bean id="urlMapping"http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/web/servlet/handler/SimpleUrlHandlerMapping.html" style="color: rgb(30, 42, 96); ">SimpleUrlHandlerMapping">
    <property name="mappings">
        <props>
            <prop key="/index.htm">indexController</prop>
        </props>
    </property>
</bean>

<bean id="viewResolver"
     http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/web/servlet/view/InternalResourceViewResolver.html" style="color: rgb(30, 42, 96); ">InternalResourceViewResolver"
      p:prefix="/WEB-INF/jsp/"
      p:suffix=".jsp" />

<bean name="indexController"
     http://static.springsource.org/spring/docs/3.0.x/javadoc-api/org/springframework/web/servlet/mvc/ParameterizableViewController.html" style="color: rgb(30, 42, 96); ">ParameterizableViewController"
      p:viewName="index" />

Overview of the Application

The application you create is comprised of two JSP pages (which can be referred to as views in MVC terminology). The first view contains an HTML form with an input field asking for the user’s name. The second view is a page that simply displays a hello message containing the user’s name.

The views are managed by a controller, which receives requests to the application and decides which views to return. It also passes to the views any information that they need to display (this is called a model). This application’s controller is named HelloController.

In a complex web application, the business logic is not contained directly in the controller. Instead, another entity, named a service, is used by the controller whenever it needs to perform some business logic. In our application, the business logic is limited to the act of processing the hello message, and for this purpose you create a HelloService.

Implementing a Service

Now that you are sure your environment is set up properly, you can begin extending the skeleton project according to your needs. Start by creating the HelloService class.

1. Click the New File (  ) button in the IDE’s toolbar. (Alternatively, press Ctrl-N; ⌘-N on Mac.)
2. Select the Java category, then select Java Class and click Next.
3. In the New Java Class wizard that displays, type in HelloService for Class Name, and enter service for Package Name to create a new package for the class.
4. Click Finish. The IDE creates the new class and opens it in the editor.

The HelloService class performs a very simple service. It takes a name as a parameter, and prepares and returns a String that includes the name. In the editor, create the following sayHello() method for the class (changes in bold).

public class HelloService {

    public static String sayHello(String name) { return "Hello " + name + "!"; }
}

Implementing the Controller and Model

You can use a SimpleFormController to handle user data and determine which view to return.

1. Open the New File wizard by pressing Ctrl-N (⌘-N on Mac). Under Categories select Spring Framework; under File Types select Simple Form Controller.
   
   NetBeans IDE provides templates for various Spring artifacts, including the Spring XML Configuration File, the AbstractController, and the SimpleFormController.
2. Click Next.
3. Name the class HelloController and create a new package for it by typing controller in the Package text field. Click Finish. The IDE creates the new class and opens it in the editor.
4. Specify controller properties by uncommenting the setter methods that display by default in the class template. To uncomment the code snippet, highlight the code as in the image below, then press Ctrl-/ (⌘-/ on Mac).
   
   Pressing Ctrl-/ (⌘-/ on Mac) toggles comments in the editor.
5. Make changes as follows (shown in bold).

   public HelloController() {
       setCommandClass(Name.class);
       setCommandName("name");
       setSuccessView("helloView");
       setFormView("nameView");
   }

   Setting the FormView enables you to set the name of the view that is used to display the form. This is the page that contains the text field allowing users to enter their name. Setting the SuccessView likewise lets you set the name of the view that should display upon a successful submit. When you set the CommandName you define the name of the command in the model. In this case, the command is the form object with request parameters bound onto it. Setting the CommandClass allows you set the name of the command class. An instance of this class gets populated and validated upon each request.

   Note that an error is flagged for Name in the setCommandClass() method:

   You now need to create the Name class as a simple bean to hold information for each request.

6. In the Projects window, right-click on the project node and choose New > Java Class. The New Java Class wizard displays.
7. Enter Name for the Class Name, and for Package select controller from the drop-down list.
8. Click Finish. The Name class is created and opens in the editor.
9. For the Name class, create a field named value, then create accessor methods (i.e., getter and setter methods) for this field. Start by declaring the value field:

   public class Name {
   
       private String value;
   
   }

   To quickly type out ‘private‘ you can type ‘pr‘ then press Tab. The ‘private‘ access modifier is automatically added to the line. This is an example of using the editor’s code templates. For a full list of code templates, choose Help > Keyboard Shortcuts Card.
   The IDE can create accessor methods for you. In the editor, right-click on value and choose Insert Code (or press Alt-Insert; Ctrl-I on Mac). In the popup menu, choose Getter and Setter.
   

10. In the dialog that displays, select the value : String option, then click OK. The getValue() and setValue() methods are added to the Nameclass:

    public String getValue() {
        return value;
    }
    
    public void setValue(String value) {
        this.value = value;
    }

11. Press Ctrl-Tab and choose HelloController to switch back to the HelloController class. Note that the previous error badge has disappeared since the Name class now exists.
12. Delete the doSubmitAction() method and uncomment the onSubmit() method. The onSubmit() method enables you to create your ownModelAndView, which is what is required here. Make the following changes:

    @Override
    protected ModelAndView onSubmit(
                HttpServletRequest request,
                HttpServletResponse response,
                Object command,
                BindException errors) throws Exception {
    
            Name name = (Name) command;
            ModelAndView mv = new ModelAndView(getSuccessView());
            mv.addObject("helloMessage", helloService.sayHello(name.getValue()));
            return mv;
    }

    As indicated above, the command is recast as a Name object. An instance of ModelAndView is created, and the success view is obtained using a getter in SimpleFormController. Finally, the model is populated with data. The only item in our model is the hello message obtained from theHelloService created earlier. You use the addObject() method to add the hello message to the model under the name helloMessage.

13. Fix import errors by right-clicking in the editor and choosing Fix Imports (Ctrl-Shift-I; ⌘-Shift-I on Mac).
    Note. Confirm that org.springframework.validation.BindException and org.springframework.web.servlet.ModelAndView are selected in the Fix All Imports dialog box.
14. Click OK. The following import statement is added to the top of the file:

    import org.springframework.web.servlet.ModelAndView;

    As stated in the API documentation, this class “represents a model and view returned by a handler, to be resolved by a DispatcherServlet. The view can take the form of a String view name which will need to be resolved by a ViewResolver object; alternatively a View object can be specified directly. The model is a Map, allowing the use of multiple objects keyed by name.”

    Note that at this stage, not all errors are fixed because the class still cannot identify the HelloService class, nor make use of its sayHello()method.

15. Within HelloController, declare a private field named HelloService:

    private HelloService helloService;

    Then create a public setter method for the field:

    public void setHelloService(HelloService helloService) {
        this.helloService = helloService;
    }

    Finally, right-click in the editor and choose Fix Imports (Ctrl-Shift-I; ⌘-Shift-I on Mac). The following statement is added to the top of the file:

    import service.HelloService;

    All errors should now be fixed.

16. Register HelloService in applicationContext.xml. Open applicationContext.xml in the editor and enter the following bean declaration:

    <bean name="helloService" />

    Spring support in the IDE includes code completion within XML configuration files for Java classes as well as bean references. To invoke code completion, press Ctrl-Space when working in the editor:
    
17. Register HelloController in dispatcher-servlet.xml. Open dispatcher-servlet.xml in the editor and enter the following bean declaration:

    <bean p:helloService-ref="helloService"/>

Implementing the Views

To implement the view for this project, you need to create two JSP pages. The first, which you will call nameView.jsp, serves as the welcome page and allows users to input a name. The other page, helloView.jsp, displays a greeting message that includes the input name. Begin by creatinghelloView.jsp.

1. In the Projects window, right-click the WEB-INF > jsp node and choose New > JSP. The New JSP File wizard opens. Name the file helloView.
2. Click Finish. The new JSP page is created in the jsp folder and opens in the editor.
3. In the editor, change the file’s title to Hello, and change the output message to retrieve the helloMessage of the ModelandView object that is created in HelloController.

   <head>
       <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
       <title>Hello</title>
   </head>
   <body>
       <h1>${helloMessage}</h1>
   </body>

4. Create another JSP page in the same manner as above, but name it nameView.
5. In the editor, add the following Spring tag library declaration to nameView.jsp.

   <%@taglib uri="http://www.springframework.org/tags" prefix="spring" %>

   This imports the Spring tag library, which contains tags useful when implementing views as JSP pages.

6. Change the contents of the <title> and <h1> tags to read: Enter Your Name.
7. Enter the following code beneath the <h1> tags:

   <spring:nestedPath path="name">
       <form action="" method="post">
           Name:
           <spring:bind path="value">
               <input type="text" name="${status.expression}" value="${status.value}">
           </spring:bind>
           <input type="submit" value="OK">
       </form>
   </spring:nestedPath>

   spring:bind allows you to bind a bean property. The bind tag provides a bind status and value, which you use as the name and value of the input field. This way, when the form is submitted, Spring will know how to extract the submitted value. Here, our command class (controller.Name) has a value property, therefore you set the path to value.

   spring:nestedPath enables you to prepend a specified path to a bean. So, when used with spring:bind as shown above, the path to the bean becomes: name.value. As you recall, the command name of HelloController is name. Therefore, this path refers to the value property of a bean named name in the page scope.

8. Change the relative entry point for the application. Currently, the project entry point is still index.htm which, as described in Running the Skeleton Project above, redirects to WEB-INF/jsp/index.jsp. You can specify an entry point for the project when it is deployed and run. In the Projects window, right-click the project node and choose Properties. The Project Properties dialog displays. Under Categories select Run. In the Relative URL field, type in /hello.htm, then click OK.At this moment you may wonder where the mapping of hello.htm to HelloController is located. You have not added a mapping to theurlMapping bean, as is the case for index.htm, the skeleton project’s welcome page. This is possible with a bit of Spring magic provided by the following bean definition in dispatcher-servlet.xml:

   <bean/>

   This bean is responsible for automatically creating an URL mapping for all controllers registered in the file. It takes the fully-qualified class name of the controller (in our case, controller.HelloController) and strips the package name and Controller suffix, then uses the result as a URL mapping. Therefore, for HelloController it creates a hello.htm mapping. This magic however does not work for controllers that are included in the Spring Framework, such as ParameterizableViewController. They require an explicit mapping.

9. In the Projects window right-click the project node and choose Run. This compiles, deploys and runs the project. Your default browser opens, displaying hello.htm as the project’s nameView:
   
   Enter your name in the text field and click enter. The helloView displays with a greeting message: