Raible Designs

Running Hosted Mode in GWT Libraries (when using Maven)

Earlier this year, I wrote about Modularizing GWT Applications with GWT-Maven. Fast forward 8 months and I'm still working with GWT and using this same technique. However, this time I'm working with the Maven GWT Plugin from Codehaus. In my last post, I wrote:

The results of modularizing your application are beneficial (shared code) and detrimental (you have to mvn install gwt-core whenever you make changes in shared classes). If you know of a way to configure the gwt-maven plugin to read sources from both gwt-core and gwt-webapp in hosted mode, I'd love to hear about it.

The good news is I found a solution for this, using the Builder Helper Maven Plugin. The GWT Maven Plugin's Productivity tip for multi-project setup has more information on how to configure this (note: we use IntelliJ and Eclipse on my project and did not need to configure this in a profile).

All was fine and dandy with this configuration until I wanted to be able to run hosted mode to develop/test everything in my library before including it in my main project. Luckily, you can still run mvn gwt:run on a JAR project. However, when you configure your pom.xml so sources are included in your JAR, you run into an issue: your *.java files will be copied to war/WEB-INF/classes and hosted mode will use these files as source rather than the ones you're editing in src/main/java.

To solve this, I changed my pom.xml to do two things:

• Only copy resources right before packaging (in the test phase).
• When packaging is complete, delete the *.java files from war/WEB-INF/classes (using Ant).

Below is the XML I used to make this possible. Please let me know if you have a way to simplify this configuration.

<plugin>
    <artifactId>maven-resources-plugin</artifactId>
    <version>2.4.1</version>
    <executions>
        <execution>
            <phase>test</phase>
            <goals>
                <goal>copy-resources</goal>
            </goals>
            <configuration>
                <outputDirectory>${project.build.outputDirectory}</outputDirectory>
                <resources>
                    <resource>
                        <directory>src/main/java</directory>
                    </resource>
                    <resource>
                        <directory>src/main/resources</directory>
                    </resource>
                </resources>
            </configuration>
        </execution>
    </executions>
</plugin>
<plugin>
    <artifactId>maven-antrun-plugin</artifactId>
    <version>1.3</version>
    <executions>
        <execution>
            <phase>package</phase>
            <goals>
                <goal>run</goal>
            </goals>
            <configuration>
                <tasks>
                    <delete>
                        <fileset dir="${project.build.outputDirectory}" includes="**/*.java"/>
                    </delete>
                </tasks>
            </configuration>
        </execution>
    </executions>
</plugin>

This solution seems to work pretty well. As far as developing your library in hosted mode, you'll need to configure two *.gwt.xml files, one that doesn't have an <entry-point> defined and one that does. Configure the one with the entry point as the <module> in your gwt-maven-plugin configuration.

As a side note, I found a few issues with the 1.1 version of the Maven GWT Archetype. Below are the steps I used to fix these issues and upgrade to GWT 1.7.0 (I realize 1.7.1 is out, but gwt-dev-1.7.1-mac.jar doesn't exist in Maven central).

First, create a new project by running the following from the command line:

mvn archetype:generate \
  -DarchetypeGroupId=org.codehaus.mojo \
  -DarchetypeArtifactId=gwt-maven-plugin \
  -DarchetypeVersion=1.1 \
  -DgroupId=com.yourcompany \
  -DartifactId=gwt-project -Dversion=1.0-SNAPSHOT -B

After creating the project, you'll need to modify the pom.xml as follows:

1. Change the gwt-maven-plugin's version to 1.1.
2. Change the ${gwtVersion} property to 1.7.0.
3. Add <runTarget>Application.html</runTarget> to the <configuration> element of the plugin.
4. Move Application.html and web.xml so they're under the "war" directory.
5. Update Application.html to prepend the GWT module name in the <script> tag.

I hope these instructions help you create modular GWT projects with Maven. This setup is working great on my current project.