Unable to execute gwt:compile during maven compile phase

Question

I am building a GWT project with Maven. I have added the gwt-maven-plugin for GWT compilation as shown below :

<dependency>
    <groupId>com.google.gwt</groupId>
    <artifactId>gwt-user</artifactId>
    <version>2.5.0</version>
    <scope>provided</scope>
</dependency>
<dependency>
    <groupId>com.google.gwt</groupId>
    <artifactId>gwt-dev</artifactId>
    <version>2.5.0</version>
    <scope>provided</scope>
</dependency>
<build>
   <plugins>
      <plugin>
          <groupId>org.codehaus.mojo</groupId>
          <artifactId>gwt-maven-plugin</artifactId>
          <version>2.5.0</version>
          <executions>
          <execution>
              <configuration>
                  <module>com.karthik.ui.MainWidgets</module>
              </configuration>
              <goals>
                   <goal>compile</goal>
              </goals>
           </execution>
           </executions>
        </plugin>
    </plugins>
</build>

I have included compile goal under executions tag expecting to execute GWT compilation during compile phase. But GWT compilation is getting executed only during package phase or when I run mvn package command.
Also I am getting a warning as shown below even though provided scope is set for gwt-dev dependency.

[WARNING] Don't declare gwt-dev as a project dependency. This may introduce complex dependency conflict

1) Why GWT compilation is not executed during compile phase?
2) What scope should I set for GWT(gwt-user, gwt-dev) dependencies to overcome the warning?

Colin Alworth Colin Alworth · Accepted Answer · 2017-10-03T10:22:46

[WARNING] Don't declare gwt-dev as a project dependency. This may introduce complex dependency conflict

This is advice, and not a requirement. There are good reasons for adding gwt-dev though:

If you write a generator
If you write a linker

If you do these things, be sure to mark gwt-dev as <scope>provided</scope>. The gwt-user dependency should also be marked as provided, generally speaking.

If you do not do these things, you should not need to include gwt-dev as a project dependency, though it might be helpful as a dependency to your plugin if you like to mix gwt-maven-plugin and gwt versions.

Why not include gwt-dev? Aside from the cases above, there are no times when you might need to reference classes in that jar - everything you need is in gwt-user (or gwt-servlet at runtime on the server). The gwt-maven-plugin will automatically add gwt-dev to your classpath so that the compiler can be run correctly.

As for the "Why GWT compilation is not executed during compile phase?":

You have specifically configured the gwt-maven-plugin to run gwt:compile, but you forgot to tell it when to run it, so it is running it at the default time - during prepare-package. Instead, you need to specify <phase>compile</phase> in the <execution> tags.

However, the compile phase might be too early - if it happens to run before your .java files are compiled to .class bytecode, the compiler will fail. Consider another time, like process-classes or later, from the lifecycle document https://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html:

process-classes post-process the generated files from compilation, for example to do bytecode enhancement on Java classes.

Unable to execute gwt:compile during maven compile phase

1 Answers