MyCommand.java

public class MyCommand extends AbstractUICommand {

	@Inject
	ProjectFactory projectFactory;

	@Override
	public UICommandMetadata getMetadata(UIContext context) {
		return Metadata.forCommand(MyCommand.class).name("toto")
				.category(Categories.create("JavaEE"));
	}

	@Override
	public void initializeUI(UIBuilder builder) throws Exception {
	}

	@Override
	public Result execute(UIExecutionContext context) throws Exception {
		final JavaClassSource javaClass = Roaster.create(JavaClassSource.class);
		javaClass.setName("MyClass").setPackage("org.helloAddon").addField().setName("myfield").setType(String.class);
		Projects.getSelectedProject(projectFactory, context.getUIContext()).getFacet(JavaSourceFacet.class).saveJavaSource(javaClass);

		return Results.success("Command 'toto' successfully executed!");
	}
}