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...
  }
 }
}