Using Spring Framework and Google App Engine for a Web Application.

Step by Step Procedure for the Hello World Application:

• Install the Google Plugin
• Create a new Web application and untick GWT (Google Web Toolkit)
• Download the latest Spring Release
• Add the Jars to the folder WEB-INF/lib

The following JAR files should be present in the folder:

Make the Following Changes to the web.xml file

<?xml version="1.0" encoding="utf-8"?>

<web-app xmlns="http://java.sun.com/xml/ns/javaee" version="2.5">
    <servlet>
        <servlet-name>dispatcher</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>dispatcher</servlet-name>
        <url-pattern>/a/*</url-pattern>
    </servlet-mapping>
</web-app>

Create a file dispatcher-servler.xml in the WEB-INF Directory

<?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.xsd
 http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

 <context:component-scan base-package="ipathshala.controllers" />

 <bean id="viewResolver"
 class="org.springframework.web.servlet.view.InternalResourceViewResolver"
 p:prefix="/WEB-INF/views/" p:suffix=".jsp" >
 <property name="viewClass" value="org.springframework.web.servlet.view.JstlView" />
 </bean>

</beans>

HelloController.java

package ipathshala.controllers;

import javax.servlet.http.HttpServletRequest;

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

import com.google.appengine.api.users.UserService;
import com.google.appengine.api.users.UserServiceFactory;

@Controller
@RequestMapping("/hello")
public class HelloController {

    private UserService userService = UserServiceFactory.getUserService();

    @RequestMapping(method = RequestMethod.GET)
    public String hello(HttpServletRequest request, ModelMap model)
    {
        String url = request.getRequestURI();
        String message;

        if(request.getUserPrincipal() != null)
        {
            message = new StringBuilder()
            .append("Hello, ")
            .append(request.getUserPrincipal().getName())
            .append("! You can <a href=\"")
            .append(userService.createLogoutURL(url))
            .append("\">Sign Out</a>.").toString();
        }else{
            message = new StringBuilder()
            .append("Please ")
            .append("<a href=\"")
            .append(userService.createLoginURL(url))
            .append("\">Sign In</a>.").toString();
        }

        model.addAttribute("message", message);

        return "hello/hello";
    }

}

This line above @RequestMapping("/hello") maps all the requests /a/hello to this controller after being examined by the DispatcherServlet.

Create a Folder views under WEB-INF and two Sub folders hello and common.

hello/hello.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@ page isELIgnored="false" %>
<%@ include file="/WEB-INF/views/common/includes.jsp" %>
<p>${message}</p>

common/includes.jsp

<%@ page session="false"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt" %>

You should now be able to click “Debug” and run the application by visiting “localhost:8888/a/hello”.

References:

• Adent Lord’s Spring 3.0 GAE article: http://www.ardentlord.com/apps/blog/show/829881-spring-3-0-on-google-app-engine
  
• GAE Documentation: http://code.google.com/appengine/docs/java/gettingstarted/
  
• Spring 3.0 Documentation: http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/
  
• Spring MVC 2.5 Tutorial: http://static.springsource.org/docs/Spring-MVC-step-by-step/