maedle

A maven plugin that transforms a maven plugin into a gradle plugin (plugin will be available soon as gradle plugin). ;-) The transformation is done in bytecode so it is independent of the programming langauge the mojo was written. So maedle should work for mojos written in Java, Groovy, Scala, Kotlin and any other language that compiles to JVM bytecode. The word "Maedle" is a contamination of maven and gradle and sounds very similar to the german word for a young girl.

What is maedle capable of? Inside a JAR it searches for classes annotated with maven's @Mojo annotation. Those classes are transformed in the following way:

An extension class is created
All attributes of the mojo class annotated with maven's @Parameter annotation are "moved" to the extension class created. All fields in the extension class will become public.
All read/write accesses to the mojo's attributes are redirected to the extension class
The Mojo class' superclass is replaced by java.lang.Object
The Mojo class' @Mojo annotation is removed
The Mojo's class gets a new constructor where an instance of the exentsion class can be passed. The exentsion instance passed is stored as class attribute
A gradle plugin class is created. This class extends Plugin<Project>. In the overriden apply method an instance of the extension class and an instance of the transformed mojo will be created and the extension is passed to the transformed mojo constructor. After that the mojo's execute method is called.
Exceptions org.apache.maven.plugin.MojoFailureException and org.apache.maven.plugin.MojoExecutionException are replaced by org.gradle.api.tasks.TaskExecutionException
Calls to maven's Logger will be replaced by call's to a Gradle Logger
META-INF entry is created which holds the information for gradle to be able to use the plugin

An example. This maven Mojo...

@Mojo(name = "greet")
public class GreeterMojo extends AbstractMojo {

	@Parameter(name = "greeter")
	private String greeter = "maedle";

	@Parameter(name = "message")
	private String message = "Message from Mojo!";

	public void execute() throws MojoExecutionException, MojoFailureException {
		if (greeter == null) {
			throw new MojoFailureException("greeter must not be null");
		}
		if (message == null) {
			throw new MojoFailureException("message must not be null");
		}
		System.out.println("Hello, " + greeter);
		System.out.println("I have a message for you: " + message);
	}

}

...gets transformed to the extension class...

public class GreeterMojoExtension {
	public String greeter = "maedle";
	public String message = "Message from Mojo!";
}

...and the rewritten mojo class...

public class GreeterMojoRewritten {

	private final GreeterMojoExtension extension;

	public GreeterMojoRewritten(GreeterMojoExtension extension) {
		this.extension = extension;
	}

	public void execute() {
		if (extension.greeter == null) {
			throw new TaskExecutionException("greeter must not be null");
		}
		if (extension.message == null) {
			throw new TaskExecutionException("message must not be null");
		}
		System.out.println("Hello, " + extension.greeter);
		System.out.println("I have a message for you: " + extension.message);
	}

}

...and a plugin class gets created

public class GreetingPlugin implements Plugin<Project> {

	@Override
	public void apply(Project project) {
		GreetingPluginExtension extension = project.getExtensions().create("greeting", GreetingPluginExtension.class);
		Task task = project.task("greet");
		task.doLast(t -> execute(extension));
	}

}

Not yet implemented

Only working if Mojo extends AbstractMojo (getLog)
@Parameter's defaultValue, (e.g. @Parameter(defaultValue = "${project.build.directory}/foobar")
@Parameter#s readOnly attribute
Nested parameter names @Parameter(property = "foo.bar.myproperty")
transform MavenProject, access jar file

Jar jarTask = (Jar) project.task("jar");
File jarFile = jarTask.getArchiveFile().getOrNull().getAsFile();

support for dependsOn

@Override
public void apply(Project project) {
	GreetingPluginExtension extension = project.getExtensions().create(EXTENSION, GreetingPluginExtension.class);
	Task task = project.task(TASK);
	task.dependsOn("jar").doLast(t -> execute(extension));
}

pfichtner/maedle

maedle