Using Guice with Google App Engine

You can use Guice with to write modular applications for Google App Engine.

Supported Builds

Google App Engine support requires Guice 2 (with or without AOP), plus the guice-servlet extension.

Setup

Servlet and Filter Registration

Configure servlets and filters by subclassing ServletModule:

package com.mycompany.myproject;

import com.google.inject.servlet.ServletModule;

class MyServletModule extends ServletModule {
  @Override protected void configureServlets() {
    serve("/*").with(MyServlet.class);
  }
}

Injector Creation

Construct your Guice injector in the getInjector() method of a class that extends GuiceServletContextListener. Be sure to include your application's servlet module in the list of modules.

package com.mycompany.myproject;

import com.google.inject.servlet.ServletModule;
import com.google.inject.servlet.GuiceServletContextListener;
import com.google.inject.Guice;
import com.google.inject.Injector;

public class MyGuiceServletContextListener extends GuiceServletContextListener {

  @Override protected Injector getInjector() {
    return Guice.createInjector(
        new MyServletModule(),
        new BusinessLogicModule());
  }
}

Web.xml Configuration

You must register both the GuiceFilter and your subclass of GuiceServletContextListener in your application's web.xml file. All other servlets and filters may be configured in your servlet module.

<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app 
   xmlns="http://java.sun.com/xml/ns/javaee" 
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
   version="2.5"> 
  <display-name>My Project</display-name>
  
 <filter>
    <filter-name>guiceFilter</filter-name>
    <filter-class>com.google.inject.servlet.GuiceFilter</filter-class>
  </filter>

  <filter-mapping>
    <filter-name>guiceFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <listener>
    <listener-class>com.mycompany.myproject.MyGuiceServletContextListener</listener-class>
  </listener>
</web-app>

WAR Layout

Ensure the AOP alliance, Guice, and Guice servlet jars are in the WEB-INF/lib directory of your .war file (or www directory):

  www/
      WEB-INF/
          lib/
              aopalliance.jar
              guice-servlet-snapshot.jar
              guice-snapshot.jar
              ...
          classes/
              ...
          appengine-web.xml
          web.xml