How do you force a maven MOJO to be executed only once at the end of a build?

Question

I have a MOJO I would like executed once, and once only after the test phase of the last project in the reactor to run.

Using:

if (!getProject().isExecutionRoot()) {
        return ;
}

at the start of the execute() method means my mojo gets executed once, however at the very beginning of the build - before all other child modules.

Answer 1

The best solution I have found for this is:

/**
 * The projects in the reactor.
 *
 * @parameter expression="${reactorProjects}"
 * @readonly
 */
private List reactorProjects;

public void execute() throws MojoExecutionException {

    // only execute this mojo once, on the very last project in the reactor
    final int size = reactorProjects.size();
    MavenProject lastProject = (MavenProject) reactorProjects.get(size - 1);
    if (lastProject != getProject()) {
        return;
    }
   // do work
   ...
}

This appears to work on the small build hierarchies I've tested with.

Answer 2

The best solution is relying on a lifecycle extension by extending your class from org.apache.maven.AbstractMavenLifecycleParticipant (see also https://maven.apache.org/examples/maven-3-lifecycle-extensions.html) which got a method afterSessionEnd added with https://issues.apache.org/jira/browse/MNG-5640 (fixed in Maven 3.2.2).