Eclipse Modeling Framework (EMF) - Persisting models via XMI

This article focus on the persistence of EMF models via XMI. It also explains how to use encryption for the XMI files. For an introduction into Eclipse EMF please see Eclipse EMF .

2. Persisting EMF models via XMI

2.1. Overview

EMF allows to store the model content via the EMF persistence framework. EMF provides XMI and XML persistence provider. By default EMF uses XMI (XML Metadata Interchange). XMI is a standard for exchanging metadata information via Extensible Markup Language (XML).

The following demonstrates how you create a EMF model instance, save it and load it again.

2.2. Example

The following is based on the EMF model created in Eclipse EMF Tutorial . Create a new plugin project "de.vogella.emf.webpage.instance". Add the following dependency to your "plugin.xml".

org.eclipse.emf.ecore
org.eclipse.emf.ecore.xmi

Tip

Objects which do not have a "contains relationship" must be added explicitly to the resource.getContents().add(). If objects are not added and not included in a contains relationship an exception is thrown when calling resource.save()

				
package writeWebpage;

import java.io.IOException;
import java.util.Collections;
import java.util.Map;

import org.eclipse.emf.common.util.URI;
import org.eclipse.emf.ecore.resource.Resource;
import org.eclipse.emf.ecore.resource.ResourceSet;
import org.eclipse.emf.ecore.resource.impl.ResourceSetImpl;
import org.eclipse.emf.ecore.xmi.impl.XMIResourceFactoryImpl;

import datamodel.website.MyWeb;
import datamodel.website.Webpage;
import datamodel.website.WebsiteFactory;
import datamodel.website.WebsitePackage;
import datamodel.website.impl.WebsitePackageImpl;

public class CreateSaveTester {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// Initialize the model
		WebsitePackage.eINSTANCE.eClass();
		// Retrieve the default factory singleton
		WebsiteFactory factory = WebsiteFactory.eINSTANCE;

		// Create the content of the model via this program
		MyWeb myWeb = factory.createMyWeb();
		Webpage page = factory.createWebpage();
		page.setName("index");
		page.setDescription("Main webpage");
		page.setKeywords("Eclipse, EMF");
		page.setTitle("Eclipse EMF");
		myWeb.getPages().add(page);

		// As of here we preparing to save the model content

		// Register the XMI resource factory for the .website extension

		Resource.Factory.Registry reg = Resource.Factory.Registry.INSTANCE;
		Map<String, Object> m = reg.getExtensionToFactoryMap();
		m.put("website", new XMIResourceFactoryImpl());

		// Obtain a new resource set
		ResourceSet resSet = new ResourceSetImpl();

		// Create a resource
		Resource resource = resSet.createResource(URI
				.createURI("website/My2.website"));
		// Get the first model element and cast it to the right type, in my
		// example everything is hierarchical included in this first node
		resource.getContents().add(myWeb);

		// Now save the content.
		try {
			resource.save(Collections.EMPTY_MAP);
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

2.3. Load an existing model

The following coding can be used to load an existing model.

				

package writeWebpage;

import java.util.Map;

import org.eclipse.emf.common.util.URI;
import org.eclipse.emf.ecore.resource.Resource;
import org.eclipse.emf.ecore.resource.ResourceSet;
import org.eclipse.emf.ecore.resource.impl.ResourceSetImpl;
import org.eclipse.emf.ecore.xmi.impl.XMIResourceFactoryImpl;

import datamodel.website.MyWeb;
import datamodel.website.WebsitePackage;
import datamodel.website.impl.WebsitePackageImpl;

public class EMFModelLoad {
	public MyWeb load() {
		// Initialize the model
		WebsitePackage.eINSTANCE.eClass();
		
		// Register the XMI resource factory for the .website extension

		Resource.Factory.Registry reg = Resource.Factory.Registry.INSTANCE;
		Map<String, Object> m = reg.getExtensionToFactoryMap();
		m.put("website", new XMIResourceFactoryImpl());

		// Obtain a new resource set
		ResourceSet resSet = new ResourceSetImpl();

		// Get the resource
		Resource resource = resSet.getResource(URI
				.createURI("website/My.website"), true);
		// Get the first model element and cast it to the right type, in my
		// example everything is hierarchical included in this first node
		MyWeb myWeb = (MyWeb) resource.getContents().get(0);
		return myWeb;
	}

}

You can then access the model content via standard Java coding.

				
package writeWebpage;

import java.util.Iterator;

import datamodel.website.MyWeb;
import datamodel.website.Webpage;

public class LoadTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// Loading the existing model
		EMFModelLoad loader = new EMFModelLoad();
		MyWeb myWeb = loader.load();
		// Accessing the model information
		System.out.println(myWeb.getDescription());
		System.out.println(myWeb.getTitle());
		// Lets see what info the webpage has
		for (Iterator<Webpage> iterator = myWeb.getPages().iterator(); iterator
				.hasNext();) {
			Webpage page = iterator.next();
			System.out.println("Name : " + page.getName());
			// We could also iterate over the Articles...
		}
	}
}

3. Appendix: Encryption

EMF has the possibility to encrypt the data model before writing it and to decrypt it before loading. The following demonstrates this.

Create an model based on the following interface.

			
package mymodel;

import org.eclipse.emf.ecore.EObject;
/**
 * @model
 */
public interface IPerson extends EObject {
	/**
	 * @model default="";
	 */
	public String getLastname();
}

Create the following factory which sets the option for encryption.

			
package factory;

import org.eclipse.emf.common.util.URI;
import org.eclipse.emf.ecore.resource.Resource;
import org.eclipse.emf.ecore.resource.impl.AESCipherImpl;
import org.eclipse.emf.ecore.xmi.XMIResource;
import org.eclipse.emf.ecore.xmi.impl.XMIResourceFactoryImpl;

public class MyXMIFactoryImpl extends XMIResourceFactoryImpl {

	@Override
	public Resource createResource(URI uri) {
		XMIResourceFactoryImpl resFactory = new XMIResourceFactoryImpl();
		XMIResource resource = (XMIResource) resFactory.createResource(uri);
		try {
			resource.getDefaultLoadOptions().put(Resource.OPTION_CIPHER,
					new AESCipherImpl("12345"));
			resource.getDefaultSaveOptions().put(Resource.OPTION_CIPHER,
					new AESCipherImpl("12345"));
		} catch (Exception e) {
			e.printStackTrace();
		}
		return resource;
	}
}

Create the following test class.

			
package load;

import java.io.IOException;
import java.util.Collections;
import java.util.Map;

import mymodel.IPerson;
import mymodel.MymodelFactory;
import mymodel.impl.MymodelPackageImpl;

import org.eclipse.emf.common.util.URI;
import org.eclipse.emf.ecore.resource.Resource;
import org.eclipse.emf.ecore.resource.ResourceSet;
import org.eclipse.emf.ecore.resource.impl.ResourceSetImpl;

import factory.MyXMIFactoryImpl;

public class Create {
	public void create() {
		MymodelPackageImpl.init();
		// Retrieve the default factory singleton
		MymodelFactory factory = MymodelFactory.eINSTANCE;

		// Create the content of the model via this program
		IPerson person = factory.createIPerson();
		person.setLastname("Lars");

		// Register the XMI resource factory for the .website extension
		Resource.Factory.Registry reg = Resource.Factory.Registry.INSTANCE;
		Map<String, Object> m = reg.getExtensionToFactoryMap();
		m.put("person", new MyXMIFactoryImpl());

		// Obtain a new resource set
		ResourceSet resSet = new ResourceSetImpl();

		// Create a resource
		Resource resource = resSet.createResource(URI
		.createURI("mymodel.person"));
		resource.getContents().add(person);

		// Now save the content.
			try {
				resource.save(Collections.EMPTY_MAP);
			} catch (IOException e) {
				e.printStackTrace();
			}
	}
	
	public void load() {
		// Initialize the model
		MymodelPackageImpl.init();
		// Register the XMI resource factory for the .website extension
		Resource.Factory.Registry reg = Resource.Factory.Registry.INSTANCE;
		Map<String, Object> m = reg.getExtensionToFactoryMap();
		m.put("person", new MyXMIFactoryImpl());
		ResourceSet resSet = new ResourceSetImpl();
		Resource resource = resSet.getResource(URI
				.createURI("mymodel.person"), true);
		try {
			IPerson person= (IPerson) resource.getContents().get(0);
			System.out.println(person.getLastname());
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args){
		Create test = new Create();
		test.create();
		test.load();
	}
}

4. Thank you

Thank you for practicing with this tutorial.

I maintain this tutorial in my private time. If you like the information please help me by using flattr or donating or by recommending this tutorial to other people.

5. Questions and Discussion

Before posting questions, please see the vogella FAQ . If you have questions or find an error in this article please use the www.vogella.de Google Group . I have created a short list how to create good questions which might also help you. .

6. Links and Literature

6.1. Source Code

Source Code of Examples

6.2. EMF Resources

http://www.eclipse.org/modeling/emf Eclipse EMF Homepage

http://www.eclipse.org/modeling/emf/docs/ EMF Documentation

http://www.ibm.com/developerworks/opensource/library/os-ecemf1 Model with the Eclipse Modeling Framework, Part 1: Create UML models and generate code

http://www.ibm.com/developerworks/opensource/library/os-ecemf2 Model with the Eclipse Modeling Framework, Part 2: Generate code with Eclipse's Java Emitter Templates

http://www.eclipse.org/m2m/atl/ ATL allows model to model transformation for EMF

6.3. vogella Resources

Eclipse Tutorials

Web development Tutorials

Android Development Tutorial

GWT Tutorial

Eclipse RCP Tutorial