Models and Eclipse EMF

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.

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 Tutorials. 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 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 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 iterator = myWeb.getPages().iterator(); iterator
    .hasNext();) {
   Webpage page = iterator.next();
   System.out.println("Name : " + page.getName());
   // We could also iterate over the Articles...
  }
 }
}

   

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 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 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();
 }
}

  

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 donating or by recommending this tutorial to other people.