GWT Maven Eclipse Plugin - Compilation Fails Due to Duplicate Class

Question

I am using Eclipse 3.5 (Galileo) with m2eclipse and GWT Eclipse plugins installed. I created a project using the gwt-maven-plugin archetype. I have created an RPC service defined with these classes:

my.package.client.DataService
my.package.client.DataServiceAsync
my.package.server.DataServiceImpl

When I run mvn clean, the target directory is removed (as exepected). When I run gwt:compile gwt:run -X -e, I get the error:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.0.2:compile (default-compile) on project MyProject: Compilation failure
C:\Devel\EclipseProjects\MyProject\target\generated-sources\gwt\my\package\client\DataServiceAsync.java:[8,7] duplicate class: my.project.client.DataServiceAsync
-> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:2.0.2:compile (default-compile) on project MyProject: Compilation failure
C:\Devel\EclipseProjects\MyProject\target\generated-sources\gwt\my\package\client\DataServiceAsync.java:[8,7] duplicate class: my.project.client.DataServiceAsync


    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:581)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.executeForkedExecutions(DefaultLifecycleExecutor.java:685)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:560)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:324)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:247)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:104)
    at org.apache.maven.cli.MavenCli.execute(MavenCli.java:427)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:157)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:121)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: org.apache.maven.plugin.CompilationFailureException: Compilation failure
C:\Devel\EclipseProjects\MyProject\target\generated-sources\gwt\my\package\client\DataServiceAsync.java:[8,7] duplicate class: my.project.client.DataServiceAsync


    at org.apache.maven.plugin.AbstractCompilerMojo.execute(AbstractCompilerMojo.java:516)
    at org.apache.maven.plugin.CompilerMojo.execute(CompilerMojo.java:114)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:105)
    at org.apache.maven.lifecycle.DefaultLifecycleExecutor.execute(DefaultLifecycleExecutor.java:577)
    ... 16 more
[ERROR] 
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException

After the failure, the target directory has been created with the following directory structure and the single file in it as such:

MyProject/target/generated-sources/gwt/my/project/client/DataServiceAsync.java

Since the target directory didn't exist before running gwt:compile gwt:run -X -e, the directories must have been created and the java class copied as part of executing the goal. So, why would the goal now complain about a duplicate class?

Any help is greatly appreciated!

Answer 1

I have found this posting which states:

If you manually create the Async interface you must disable the generateAsync goal in the plugin configuration

The fix was to remove <goal>generateAsync</goal> from my pom.xml. The plugin config now looks like:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>gwt-maven-plugin</artifactId>
    <version>1.2</version>
    <executions>
        <execution>
            <goals>
                <goal>compile</goal>
                <goal>test</goal>
            </goals>
        </execution>
    </executions>
    <configuration>
        <runTarget>my.package.Application/Application.html</runTarget>
    </configuration>
</plugin>

Answer 2

You might actually have generated a duplicate class.

There is a "generateAsync" goal in pom.xml which takes care of generating Async classes for each service You create. If You have this You DO NOT NEED to create a Async version manually.

If You do then You will get "Duplicate Class" error.