Sample code for http://me-at-big.blogspot.co.at/2013/07/developing-exercises-for-model.html

AbstractModelToModelTransformation.java

package at.ac.tuwien.big.me.util;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.HashMap;
import java.util.Objects;

import org.eclipse.emf.ecore.EObject;
import org.eclipse.emf.ecore.EPackage;
import org.eclipse.emf.ecore.resource.ResourceSet;
import org.eclipse.emf.ecore.resource.impl.ResourceSetImpl;
import org.eclipse.emf.ecore.xmi.impl.XMIResourceImpl;

/**
 * Base class for M2M transformations
 */
public abstract class AbstractModelToModelTransformation {

    private final ResourceSet emfResourceSet = new ResourceSetImpl();
    protected final EPackage inPackage;
    protected final EPackage outPackage;

    protected AbstractModelToModelTransformation(EPackage inOut) {
        this(inOut, inOut);
    }

    protected AbstractModelToModelTransformation(EPackage in, EPackage out) {
        this.inPackage = Objects.requireNonNull(in, "in");
        this.outPackage = Objects.requireNonNull(out, "out");
    }

    protected EObject loadXmi(String path) throws FileNotFoundException,
            IOException {
        XMIResourceImpl resource = new XMIResourceImpl();
        resource.load(new FileInputStream(path), new HashMap<Object, Object>());
        return resource.getContents().get(0);
    }

    protected void saveXmi(String path, EObject rootObject)
            throws FileNotFoundException, IOException {
        XMIResourceImpl resource = new XMIResourceImpl();
        resource.getContents().add(rootObject);
        resource.save(new FileOutputStream(path), new HashMap<Object, Object>());
    }

    public void transform(String inputXmiPath, String outputXmiPath)
            throws IOException {
        emfResourceSet.getPackageRegistry()
                .put(inPackage.getNsURI(), inPackage);
        emfResourceSet.getPackageRegistry().put(outPackage.getNsURI(),
                outPackage);

        EObject rootIn = loadXmi(inputXmiPath);
        EObject rootOut = doTransform(rootIn);

        saveXmi(outputXmiPath, rootOut);
    }

    protected abstract EObject doTransform(EObject in);
}

atl-vs-xtend.txt

-- ATL rule
rule Rating2Message { 
    from r: questionary!Rating
    to m: webmetamodel!Message (
        value <- r.lowerPointLimit,
        text <- r.name + '\n' + r.explainatoryText
    )
}
// Xtend method
def Message resultMessage(Rating r) { 
    val m = factory.createMessage()
    m.value = r.lowerPointLimit        
    m.text = r.name + '\n' + r.explainatoryText
    return m;
}
-- ATL rule
rule RatingScheme2ResultWindow { 
    from rs: questionary!RatingScheme
    to rw: webmetamodel!ResultWindow (
        resultMessages <- rs.ratings     
    )
}
// Xtend method
def ResultWindow resultWindow(RatingScheme rs) { 
    val w = factory.createResultWindow()
    w.resultMessages.addAll( rs.ratings.map[rm|resultMessage(rm)] )
    return w;
}

IdentityTransformation.java

package at.ac.tuwien.big.me.example;

import at.ac.tuwien.big.me.util.AbstractModelToModelTransformation;
// import SomePackage here

public class IdentityTransformation extends 
    AbstractModelToModelTransformation {

    public IdentityTransformation() {
        super(SomePackage.eINSTANCE);
    }

    @Override
    protected EObject doTransform(EObject in) {
        return in;
    }
}

LICENSE.md

http://www.eclipse.org/legal/epl-v10.html