ComputerScience: How to run Simple Hello World Application in Spring using Eclipse?

Things We Need

Before we starts with our first Hello World Struts 2 Example, we will need few tools.

JDK 1.5 above (download)

Tomcat 5.x above or any other container (Glassfish, JBoss, Websphere, Weblogic etc) (download)

Eclipse 3.2.x above (download)

Spring 3.0 MVC JAR files:(download). Following are the list of JAR files required for this application.

commons-logging-1.0.4.jar

jstl-1.2.jar

org.springframework.asm-3.0.1.RELEASE-A.jar

org.springframework.beans-3.0.1.RELEASE-A.jar

org.springframework.context-3.0.1.RELEASE-A.jar

org.springframework.core-3.0.1.RELEASE-A.jar

org.springframework.expression-3.0.1.RELEASE-A.jar

org.springframework.web.servlet-3.0.1.RELEASE-A.jar

org.springframework.web-3.0.1.RELEASE-A.jar

Note that depending on the current version of Spring MVC, the version number of above jar files may change.

Our Goal

Our goal is to create a basic Spring MVC application using latest 3.0 version. There will be an index page which will display a link “Say Hello” to user. On clicking this link, user will be redirected to another page hello which will display a message “Hello World, Spring 3.0!”.

Getting Started

Let us start with our first Spring 3.0 MVC based application.

Open Eclipse and goto File -> New -> Project and select Dynamic Web Project in the New Project wizard screen.

After selecting Dynamic Web Project, press Next.

Write the name of the project. For example Spring3MVC. Once this is done, select the target runtime environment (e.g. Apache Tomcat v6.0). This is to run the project inside Eclipse environment. After this press Finish.

Once the project is created, you can see its structure in Project Explorer.

Now copy all the required JAR files in WebContent > WEB-INF > lib folder. Create this folder if it does not exists.

The Spring Controller Class

We will need a spring mvc controller class that will process the request and display a “Hello World” message. For this we will create a package net.viralpatel.spring3.controller in the source folder. This package will contain the Controller file.

Create a class called HelloWorldController in net.viralpatel.spring3.controller package and copy following content into it.

File: net.viralpatel.spring3.controller.HelloWorldController

?
package net.viralpatel.spring3.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;
@Controller
public class HelloWorldController {
    @RequestMapping("/hello")
    public ModelAndView helloWorld() {
        String message = "Hello World, Spring 3.0!";
        return new ModelAndView("hello", "message", message);
    }
}

Note that we have annotated the HelloWorldController class with @Controller and@RequestMapping("/hello") on line 7 and 10. When Spring scans our package, it will recognize this bean as being a Controller bean for processing requests. The @RequestMapping annotation tells Spring that this Controller should process all requests beginning with /hello in the URL path. That includes /hello/*and /hello.html.

The helloWorld() method returns ModelAndView object. The ModelAndView object tries to resolve to a view named “hello” and the data model is being passed back to the browser so we can access the data within the JSP. The logical view name will resolve to "/WEB-INF/jsp/hello.jsp". We will discuss this shortly how the logical name “hello” which is return in ModelAndView object is mapped to path /WEB-INF/jsp/hello.jsp.

The ModelAndView object also contains a message with key “message” and value “Hello World, Spring 3.0!”. This is the data that we are passing to our view. Normally this will be a value object in form of java bean that will contain the data to be displayed on our view. Here we are simply passing a string.

The View: Create JSP

To display the hello world message we will create a JSP. Note that this JSP is created in folder /WEB-INF/jsp. Create hello.jsp under WEB-INF/jsp directory and copy following content into it.

File: WEB-INF/jsp/hello.jsp

?
<html>
<head>
    <title>Spring 3.0 MVC Series: Hello World - ViralPatel.net</title>
</head>
<body>
    ${message}
</body>
</html>

The above JSP simply display a message using expression ${message}. Note that the name “message” is the one which we have set in ModelAndView object with the message string.

Also we will need an index.jsp file which will be the entry point of our application. Create a file index.jsp under WebContent folder in your project and copy following content into it.

File: WebContent/index.jsp

?
<html>
<head>
    <title>Spring 3.0 MVC Series: Index - ViralPatel.net</title>
</head>
<body>
    <a href="hello.html">Say Hello</a>
</body>
</html>

Mapping Spring MVC in WEB.xml

As discussed in the previous article (Introduction to Spring 3.0 MVC), the entry point of Spring MVC application will be the Servlet define in deployment descriptor (web.xml). Hence we will define an entry oforg.springframework.web.servlet.DispatcherServlet class in web.xml.

Open web.xml file which is under WEB-INF folder and copy paste following code.

File: WEB-INF/web.xml

?
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    id="WebApp_ID" version="2.5">
    <display-name>Spring3MVC</display-name>
    <welcome-file-list>
        <welcome-file>index.jsp</welcome-file>
    </welcome-file-list>
    <servlet>
        <servlet-name>spring</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>spring</servlet-name>
        <url-pattern>*.html</url-pattern>
    </servlet-mapping>
</web-app>

The above code in web.xml will map DispatcherServlet with url pattern *.html. Also note that we have define index.jsp as welcome file.

One thing to note here is the name of servlet in <servlet-name> tag in web.xml. Once the DispatcherServlet is initialized, it will looks for a file name [servlet-name]-servlet.xml in WEB-INF folder of web application. In this example, the framework will look for file called spring-servlet.xml.

Spring configuration file

Create a file spring-servlet.xml in WEB-INF folder and copy following content into it.

File: WEB-INF/spring-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:p="http://www.springframework.org/schema/p"
    xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd">
    <context:component-scan
        base-package="net.viralpatel.spring3.controller" />
    <bean id="viewResolver"
        class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass"
            value="org.springframework.web.servlet.view.JstlView" />
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>
</beans>

In the above xml configuration file, we have defined a tag <context:component-scan>. This will allow Spring to load all the components from package net.viralpatel.spring3.controller and all its child packages. This will load our HelloWorldController class. Also we have defined a bean viewResolver. This bean will resolve the view and add prefix string /WEB-INF/jsp/ and suffix .jsp to the view in ModelAndView. Note that in our HelloWorldController class, we have return a ModelAndView object with view name “hello”. This will be resolved to path /WEB-INF/jsp/hello.jsp.

You may want to run the application now and see the result. I assume you have already configured Tomcat in eclipse. All you need to do:

Open Server view from Windows > Show View > Server. Right click in this view and select New > Server and add your server details.

To run the project, right click on Project name from Project Explorer and select Run as > Run on Server (Shortcut: Alt+Shift+X, R)

ComputerScience

Friday, May 11, 2012

How to run Simple Hello World Application in Spring using Eclipse?

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