m2e: Generated code with exec-maven-plugin

Question

I have been using m2eclipse for 2 years or so and have now switched to m2e.

Unfortunately, this has broken some functionality for me.

In many projects, I have generated Java code, usually generated through a main class in a library project. Here's a typical setup:

<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>exec-maven-plugin</artifactId>
    <executions>
        <execution>
            <id>generateDTOs</id>
            <phase>generate-sources</phase>
            <goals>
                <goal>java</goal>
            </goals>
            <configuration>
                <classpathScope>test</classpathScope>
                <mainClass>com.somecompany.SomeCodeGenerator</mainClass>
                <arguments>
                    <argument>${project.build.directory}/generated-sources/foo</argument>
                    <argument>${project.basedir}/path/to/a/config/file</argument>
                    <argument>more arguments</argument>
                </arguments>
            </configuration>
        </execution>
    </executions>
</plugin>
<plugin>
    <groupId>org.codehaus.mojo</groupId>
    <artifactId>build-helper-maven-plugin</artifactId>
    <executions>
        <execution>
            <id>addDtoSourceFolder</id>
            <goals>
                <goal>add-source</goal>
            </goals>
            <phase>process-sources</phase>
            <configuration>
                <sources>
                    <source>${project.build.directory}/generated-sources/foo</source>
                </sources>
            </configuration>
        </execution>
    </executions>
</plugin>

Previously, I would just have to import that project with eclipse as a maven project, the code would automatically be executed and the source folder added to the eclipse project.

Now, m2e has installed a "connector" for the buildhelper plugin, so the source folder is created, but I have to manually trigger code generation by executing Run As > Maven > generate-sources. This is really annoying, I would like the maven build to respond to pom.xml changes, Project > Clean ..., SVN Updates, Eclipse startup etc. as it previously did.

What can I do to make m2e work like m2eclipse?

Answer 1

You have to tell M2E that it's okay to run your code generator as part of the Eclipse build:

<project>
  <build>
     [...]
     <pluginManagement>
      <plugins>
        <!--This plugin's configuration is used to store Eclipse m2e settings only. It has no influence 
          on the Maven build itself. -->
        <plugin>
          <groupId>org.eclipse.m2e</groupId>
          <artifactId>lifecycle-mapping</artifactId>
          <version>1.0.0</version>
          <configuration>
            <lifecycleMappingMetadata>
              <pluginExecutions>
                <pluginExecution>
                  <pluginExecutionFilter>
                    <groupId>org.codehaus.mojo</groupId>
                    <artifactId>exec-maven-plugin</artifactId>
                    <versionRange>[,)</versionRange>
                    <goals>
                      <goal>java</goal>
                    </goals>
                  </pluginExecutionFilter>
                  <action>
                    <execute/>
                  </action>
                </pluginExecution>
              </pluginExecutions>
            </lifecycleMappingMetadata>
          </configuration>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

Notes:

1. It's important to put this configuration in the pluginManagement section, not directly under plugins.
2. This will cause M2E to perform all java executions specified in your POM as part of every Eclipse build. This means they will run often and be a big nuisance if they are slow. I'm not sure how you would get M2E to run some of them and skip others. You'd probably have to place the unwanted executions in profiles.