This page documents the basic usage of the Maven invocation API.

Hello, World

The simplest possible way to use the invocation API is to construct the invoker and request at the same time, and simply call invoker.execute(request). In this example, we don't care about the build result:

InvocationRequest request = new DefaultInvocationRequest();
request.setPomFile( new File( "/path/to/pom.xml" ) );
request.setGoals( Collections.singletonList( "install" ) );

Invoker invoker = new DefaultInvoker();
invoker.execute( request );

This code will execute a new Maven build to the install lifecycle phase for the project defined at /path/to/pom.xml. If the build fails, we will remain blissfully ignorant...

Checking the Exit Code

If we wanted to detect a build failure in the above example, we could simply add the following lines:

InvocationResult result = invoker.execute( request );

if ( result.getExitCode() != 0 )
    throw new IllegalStateException( "Build failed." );

This will retrieve the exit code from the invocation result, and throw an exception if it's not 0 (the traditional all-clear code). Note that we could capture the build output by adding an InvocationOutputHandler instance to either the invoker or the request.

Caching the Invoker

Since you can specify global options for Maven invocations via the Invoker configuration, it will often make sense to configure a single Invoker instance, and reuse it over multiple method calls:

// we will always call the same goals...
private static final String[] GOALS_ARRAY = { "clean", "site-deploy" };

private static final List PUBLISH_GOALS = Arrays.asList( GOALS_ARRAY );

// define a field for the Invoker instance.
private final Invoker invoker;

// now, instantiate the invoker in the class constructor...
public SomeClass( File localRepositoryDir )
    Invoker i = new DefaultInvoker();
    i.setLocalRepositoryDirectory( localRepositoryDir );
    this.invoker = i;

// this method will be called repeatedly, and fire off new builds...
public void publishSite( File siteDirectory ) throws PublishException
    InvocationRequest request = new DefaultInvocationRequest();
    request.setBaseDirectory( siteDirectory );
    request.setInteractive( false );
    request.setGoals( PUBLISH_GOALS );
    InvocationResult result = invoker.execute( request );
    if ( result.getExitCode() != 0 )
        if ( result.getExecutionException() != null )
            throw new PublishException( "Failed to publish site.",
                                        result.getExecutionException() );
            throw new PublishException( "Failed to publish site. Exit code: " + 
                                         result.getExitCode() );

As you can see, we're using the same local repository location (since the site-generation artifacts will most likely be common to most sites), the same invoker instance (it's configured, we may as well reuse it), and the same set of goals per build. We can actually accommodate a fairly complex configuration of the Invoker without adding complexity to the publishSite method in this manner.

Configuring the Maven Home Directory

You can use the method Invoker.setMavenHome() to specify which Maven executable it should use. If you don't provide an explicit value for this setting, the Invoker will automatically try to detect a Maven installation by evaluating the system property maven.home and the environment variable M2_HOME.

Note: If you use the invocation API in tests run by the Maven Surefire Plugin, you need to tell Surefire to pass the system property maven.home to the tests in order for the automatic Maven detection to work: