More Maven Plugin Tips

I’ve been writing a couple more Maven plugins recently, including one to start/stop groups of Docker containers. I wanted to extend my previous tips with three new tips I’ve found really helpful.

Tip 7: Don’t Do Any Work In Your Mojo Class

I’ve used this really effectively. Create a POJO class to do the heavy lifting for you. It’s much easier to test this class without the Maven infrastructure. In my plugin I’ve create DockerOrchestator. This has methods such as clean, start and stop.

We can create a common parent class that creates the delegate:

abstract class AbstractDockerMojo extends AbstractMojo {

    @Parameter(defaultValue = DEFAULT_HOST, property = "docker.host", required = true)
    private URI host;

    ...

    @Override
    public final void execute() throws MojoExecutionException, MojoFailureException {
        try {
	        doExecute(new DockerOrchestrator(...));
        } catch (Exception e) {
            throw new MojoExecutionException(e.getMessage(), e);
        }
    }
    
    protected abstract void doExecute(DockerOrchestrator orchestrator) throws Exception;
    ...

Then each sub-class can just call the appropriate method. There’s almost nothing to test.

@Mojo(name = "start", defaultPhase = LifecyclePhase.PRE_INTEGRATION_TEST)
public class StartMojo extends AbstractDockerMojo {

    @Override
    protected void doExecute(DockerOrchestrator orchestrator) {
        orchestrator.start();
    }
}

Tip 8: Avoid The Invoker Plugin

It’s really slow and the output is really hard to read! If you extracted your tasks to their own class, you can create tests that run as part of the integration-test phase using the Maven Failsafe Plugin.

Tip 9: Create An Appender For SLF4J

I’ve used this a couple of times. If you create you own appender, like the one I made for my plugin, and add MavenLogAppender.setLog(getLog()) to your execute method. You can use SLF4J for your logging. Better still, if you use a library that uses any of the common logging frameworks (Apache, Log4j etc.), then they will also log to the console.

I hope these tips help you to write you plugin quicker and easier!