Limitations

A restriction of this plugin is that it will search for gwt modules and host pages only in the first classpath source folder. Using a Maven / Eclipse integration like m2eclipse, this one will be your sourceDirectory (src/main/java). You'll have to move your gwt.xml files in this folder, instead of the standard Maven resource directory. See Google Eclipse Plugin issue #1597

Another bigger restriction of this plugin, is that it requires the hosted mode webapp to use /war directory as web application root. We will have to change the maven-war-plugin setup to use this folder and not the default src/main/webapp path, but will keep the latest to host the web.xml deployment descriptor. We can then have a dedicated hosted mode one where we register stub RPC-servlets for testing purpose. The 'real' web application may be long to start and require more complex resources, like a JDBC DataSource, and we can still run functionnal tests on it using the noserver option. See Google Eclipse Plugin issue #1515

Project layout

Your maven project will end something like this. Please note the Module.gwt.xml module descriptor located in src/main/java directory :

  pom.xml
  |_src
  |  |_main
  |     |_java
  |     |  |_ com/mycompany/gwt/Module.gwt.xml
  |     |  |_ com/mycompany/gwt/client
  |     |  |  |_ ModuleEntryPoint.java
  |     |_resources
  |     |_webapp
  |       |_WEB-INF
  |         |_web.wml
  |_war
    |_Module.html
    |_WEB-INF
       |_web.wml

The war folder will be used to host your test web application (used in hosted mode) where you'll put stub RPC servlets. Your real web application can be used for more advanced integration testing with the noserver option.

Maven configuration

Your Maven configuration will be something like this :

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
                                     http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.mycompany</groupId>
  <artifactId>webapp</artifactId>
  <packaging>war</packaging>
  <version>1.0-SNAPSHOT</version>

  <dependencies>
    <dependency>
      <groupId>com.google.gwt</groupId>
      <artifactId>gwt-user</artifactId>
      <scope>provided</scope>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>gwt-maven-plugin</artifactId>
        <version>1.1</version>
        <executions>
          <execution>
            <goals>
              <goal>compile</goal>
            </goals>
          </execution>
        </executions>
        <configuration>
          <runTarget>com.mycompany.gwt.Module/Module.html</runTarget>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-war-plugin</artifactId>
        <version>2.0.2</version>
        <configuration>
          <warSourceDirectory>war</warSourceDirectory>
          <webXml>src/main/webapp/WEB-INF/web.xml</webXml>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

With this setup, you can start your GWT module with a single right-clik in your Eclispe IDE with Run as : Web application.

You can the edit your java code and just hit refresh to see changes applied in the hosted browser.

Eclipse configuration

Import your maven project into eclipse using m2eclipse import wizard (or your prefered tooling). Manually enable GWT on the project from project preference by setting the Use Google Web Toolkit checkbox. Eclipse will add a new ClassPath container for GWT. Please check you use the same version of GWT in your maven configuration and in eclipse preferences.

Run the gwt:eclipse goal (using m2eclipse Maven2 > build...) to setup your environment and create the launch configuration for your GWT modules. The plugin expect the HTML host page to be named as the module and put in the module public subdirectory. If you don't use this convention yopu will have to edit manually the launch configuration.

Server side components and RPC

We use the /war folder to host our hosted-mode web application. It's web.xml deployment descriptor is dedicated to hosted mode and will be replaced by the src/main/webapp/WEB-INF one when building the WAR. This is a simple way to setup custom RPC servlets for testing and not require a complex setup (DataSource, Security, Dependency Injection... ) for quick hosted mode testing.

The gwt:eclipse goal will setup the /war folder as an exploded webapp, ready for lauching GWT hosted server. Please note the Google Eclipse Plugin 1.0.1 still uses the deprecated GWTShell and does not support servlets defined in the /war/WEB-INF/web.xml, so you must declare your (test) servlets in the module descriptor using a servlet element :

  <servlet class="org.codehaus.mojo.gwt.test.server.HelloRemoteServlet" path="/org.codehaus.mojo.gwt.test.Hello/Hello"/>

This one will be ignored after your GWT module has been compiled into JavaScript.

Multiproject setup

Big projects may want to split the client-side application in modules, typically using Maven support for multiprojects. The project layout will the become something like this (maybe with some more classes) :

  pom.xml // reactor project
  |_domain // shared with other (GWT or Java) projects
  |  |_src
  |    |_main
  |      |_java
  |      |  |_ com/mycompany/domain
  |      |  |  |_ User.java  
  |      |_resources
  |      |  |_ com/mycompany/Domain.gwt.xml
  |_webapp
     |_src
     |  |_main
     |    |_java
     |    |  |_ com/mycompany/gwt/Module.gwt.xml // inherits Domain.gwt.xml
     |    |  |_ com/mycompany/gwt/client
     |    |  |  |_ ModuleEntryPoint.java
...

When using Eclipse-Maven integration like the m2eclipse plugin, other maven projects open in the workspace will be automagically resolved as projects (instead of JARs). When the referenced project is well configured(*) as a GWT module project, changes to java sources will be available in the hosted browser with a simple refresh with no requirement to repackage the modules.

(*) A "well configured GWT module project" is expected to have Java sources copied as resources in the project build outputDirectory (using gwt:resource goal) and a dedicated gwt.xml module file to define the required inherits.

The gwt-maven-plugin src/it/reactor project can be reviewed as a demonstrating sample of this setup.