Shows how use JMerger to merge generated and hand-crafted code

MergingGenerator.java

// --- Imports ---

import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Set;
import java.util.TreeSet;

import org.eclipse.core.resources.IFile;
import org.eclipse.core.resources.IWorkspace;
import org.eclipse.core.resources.IWorkspaceRunnable;
import org.eclipse.core.resources.ResourcesPlugin;
import org.eclipse.core.runtime.CoreException;
import org.eclipse.core.runtime.IProgressMonitor;
import org.eclipse.emf.codegen.ecore.generator.GeneratorAdapterFactory;
import org.eclipse.emf.codegen.ecore.genmodel.GenModel;
import org.eclipse.emf.codegen.ecore.genmodel.GenModelFactory;
import org.eclipse.emf.codegen.ecore.genmodel.generator.GenModelGeneratorAdapterFactory;
import org.eclipse.emf.codegen.merge.java.JControlModel;
import org.eclipse.emf.codegen.merge.java.JMerger;
import org.eclipse.emf.codegen.merge.java.JPatternDictionary;
import org.eclipse.emf.codegen.merge.java.facade.JCompilationUnit;
import org.eclipse.emf.codegen.merge.java.facade.ast.ASTFacadeHelper;
import org.eclipse.emf.codegen.util.CodeGenUtil;
import org.eclipse.emf.ecore.EAttribute;
import org.eclipse.emf.ecore.EClass;
import org.eclipse.emf.ecore.EObject;
import org.eclipse.emf.ecore.EOperation;
import org.eclipse.emf.ecore.EPackage;
import org.eclipse.emf.ecore.EReference;
import org.eclipse.jdt.core.ICompilationUnit;
import org.eclipse.jdt.core.IPackageFragment;
import org.eclipse.jdt.core.IPackageFragmentRoot;
import org.eclipse.jdt.core.JavaModelException;


// --- Code ---
		IPackageFragment pkg = ...;
		ICompilationUnit compilationUnit = pkg.getCompilationUnit(...);

    String compilationUnitContent = ...;
		if (compilationUnit.exists()) {						
			IWorkspaceRunnable mergeRunnable = new IWorkspaceRunnable() {
				
				@Override
				public void run(IProgressMonitor monitor) throws CoreException {
					ICompilationUnit workingCopy = compilationUnit.getWorkingCopy(monitor);
					try {						
					    JControlModel controlModel = new JControlModel();

						GenModel genModel = GenModelFactory.eINSTANCE.createGenModel();

						// create adapter factory
						GeneratorAdapterFactory adapterFactory = GenModelGeneratorAdapterFactory.DESCRIPTOR.createAdapterFactory();
						adapterFactory.setGenerator(new org.eclipse.emf.codegen.ecore.generator.Generator());
						adapterFactory.initialize(genModel);

						// get merge rules URI
						String mergeRulesURI = adapterFactory.getGenerator().getOptions().mergeRulesURI;
					    
					    controlModel.initialize(CodeGenUtil.instantiateFacadeHelper(ASTFacadeHelper.class.getCanonicalName()), mergeRulesURI);
					    
						JMerger jMerger = new JMerger(controlModel);												
						
						JCompilationUnit scu = jMerger.createCompilationUnitForContents(compilationUnitContent.toString());
						jMerger.setSourceCompilationUnit(scu);
						
						JCompilationUnit tcu = jMerger.createCompilationUnitForContents(workingCopy.getSource());
						jMerger.setTargetCompilationUnit(tcu);
						
						jMerger.merge();
						
						String newContent = jMerger.getTargetCompilationUnitContents();
						if (!workingCopy.getSource().equals(newContent)) {
							workingCopy.getBuffer().setContents(newContent);
							workingCopy.commitWorkingCopy(false, monitor);
						}						
					} finally {
						workingCopy.discardWorkingCopy();
					}					
				}
			};
			ResourcesPlugin.getWorkspace().run(
					mergeRunnable, 
					ResourcesPlugin.getWorkspace().getRoot(), 
					IWorkspace.AVOID_UPDATE, 
					monitor);
		} else {	
			pkg.createCompilationUnit(..., compilationUnitContent, false, monitor);
		}