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My generation fails with a 'package not found' exception

Q : Whenever I launch an Acceleo generation, it fails with the message package with URI '*' not found'.

A : This error message indicates that the package which NsURI is '*' hasn't been registered in the Package registry. Most of the time, that means you either a) launched your program standalone and didn't register the package correctly or b) you haven't installed the plug-in that provides that metamodel.

Solving it is easy : it is a matter of registering the needed packages (and, optionally, resource factories). How is it done? Here is the most classic example with UML :

Package with uri '' not found.

What do I need to do for my UML model to be loadable :

EPackage.Registry.INSTANCE.put(UMLPackage.eNS_URI, UMLPackage.eINSTANCE); Resource.Factory.Registry.INSTANCE.getExtensionToFactoryMap().put(UMLResource.FILE_EXTENSION, UMLResource.Factory.INSTANCE);

The same goes for every metamodel you might need, simply change UMLPackage by XxxPackage according to your metamodel. The Resource Factory is mandatory for UML, but your metamodel might not need one; simply ignore this line if you don't have a custom factory.

You need these two lines to be before the point where your model is loaded. For Acceleo, this is done in the generated Java launcher : simply change the implementation of the registerPackages and registerResourceFactories method to add these needed lines.

How can I run a generation in a standalone environment?

Q : Can I run an Acceleo generation outside of Eclipse?

A : Yes, Acceleo has been developed with standalone execution in mind. All you have to do is to launch the main method of the generated Java launcher.

How can I compile my mtl files in a standalone environment?

Q : Can I use the Acceleo compiler to recompile mtl files outside of Eclipse?

A : Yes, though this requires a little more work than "simply" launching the generation. The easiest is to define your own ANT task for that job. It should extend the AcceleoCompiler ANT task that's provided along with Acceleo (the latest version of the jar containing this class can be retrieved here, or you could simply look at its source code and reproduce something similar).

The bare minimum your class would need in order to compile mtl files in a standalone environment would be :

 public class AcceleoStandaloneCompiler extends AcceleoCompiler {
   public void execute() throws BuildException {
   public void registerResourceFactories() {
     Resource.Factory.Registry.INSTANCE.getExtensionToFactoryMap().put("ecore", new EcoreResourceFactoryImpl());
     Resource.Factory.Registry.INSTANCE.getExtensionToFactoryMap().put(IAcceleoConstants.EMTL_FILE_EXTENSION, new EMtlResourceFactoryImpl());
     // Uncomment the following if you need to use UML models
     // Resource.Factory.Registry.INSTANCE.getExtensionToFactoryMap().put(UMLResource.FILE_EXTENSION, UMLResource.Factory.INSTANCE);
   public void registerPackages() {
     // Uncomment if you need to use UML models
     // EPackage.Registry.INSTANCE.put(UMLPackage.eNS_URI, UMLPackage.eINSTANCE);
     // Uncomment if you need to use UML models saved with on old version of MDT/UML (you might need to change the URI's version number)
     // EPackage.Registry.INSTANCE.put("", UMLPackage.eINSTANCE);
   public void registerLibraries() {
     CodeSource acceleoModel = MtlPackage.class.getProtectionDomain().getCodeSource();
     if (acceleoModel != null) {
       String libraryLocation = acceleoModel.getLocation().toString();
       if (libraryLocation.endsWith(".jar")) {
         libraryLocation = "jar:" + libraryLocation + '!';
       URIConverter.URI_MAP.put(URI.createURI(""), URI.createURI(libraryLocation + "/model/mtlstdlib.ecore"));
       URIConverter.URI_MAP.put(URI.createURI(""), URI.createURI(libraryLocation + "/model/mtlnonstdlib.ecore"));
     } else {
       System.err.println("Coudln't retrieve location of plugin 'org.eclipse.acceleo.model'.");

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