LayoutExtensionFactory.java

//------------------------------------------------------------------------------
// Copyright (c) 2005, 2007 IBM Corporation and others.
// All rights reserved. This program and the accompanying materials
// are made available under the terms of the Eclipse Public License v1.0
// which accompanies this distribution, and is available at
// http://www.eclipse.org/legal/epl-v10.html
//
// Contributors:
// IBM Corporation - initial implementation
//------------------------------------------------------------------------------
package org.eclipse.epf.library.layout;

import java.util.HashMap;
import java.util.Map;

import org.eclipse.core.runtime.IConfigurationElement;
import org.eclipse.core.runtime.IExtension;
import org.eclipse.core.runtime.IExtensionPoint;
import org.eclipse.core.runtime.IExtensionRegistry;
import org.eclipse.core.runtime.Platform;
import org.eclipse.epf.library.LibraryPlugin;
import org.osgi.framework.Bundle;

/**
 * Manages the LayoutExtension contributions
 * 
 * @author Jinhua Xi
 * @since 1.0
 */
public class LayoutExtensionFactory {

	/**
	 * The extension point namespace.
	 */
	public static final String EXTENSION_POINT_NAMESPACE = "org.eclipse.epf.library"; //$NON-NLS-1$

	/**
	 * The extension point name.
	 */
	public static final String EXTENSION_POINT_NAME = "elementLayoutExtensions"; //$NON-NLS-1$

	/**
	 * The "class" attribute name.
	 */
	public static final String CLASS_ATTRIB_NAME = "class"; //$NON-NLS-1$

	/**
	 * The "id" attribute name.
	 */
	public static final String ID_ATTRIB_NAME = "id"; //$NON-NLS-1$

	// The shared instance.
	private static LayoutExtensionFactory instance = null;

	// A map of library manager configuration elements.
	private Map<String, LayoutExtensionElement> layoutElements = new HashMap<String, LayoutExtensionElement>();

	/**
	 * Returns the shared instance.
	 */
	public static synchronized LayoutExtensionFactory getInstance() {
		if (instance == null) {
			instance = new LayoutExtensionFactory();
		}
		return instance;
	}

	/**
	 * Creates a new instance.
	 */
	private LayoutExtensionFactory() {
		init();
	}

	/**
	 * Performs the necessary initialization.
	 */
	protected void init() {
		// Process the "org.eclipse.epf.library.libraryManagers" extension point
		// contributors.
		IExtensionRegistry extensionRegistry = Platform.getExtensionRegistry();
		IExtensionPoint extensionPoint = extensionRegistry.getExtensionPoint(
				EXTENSION_POINT_NAMESPACE, EXTENSION_POINT_NAME);
		if (extensionPoint != null) {
			IExtension[] extensions = extensionPoint.getExtensions();
			for (int i = 0; i < extensions.length; i++) {
				IExtension extension = extensions[i];
				String pluginId = extension.getNamespaceIdentifier();
				Bundle bundle = Platform.getBundle(pluginId);
				IConfigurationElement[] configElements = extension
						.getConfigurationElements();
				for (int j = 0; j < configElements.length; j++) {
					IConfigurationElement configElement = configElements[j];
					try {
						String className = configElement
								.getAttribute(CLASS_ATTRIB_NAME);
						String id = configElement
								.getAttribute(ID_ATTRIB_NAME);
						if (className != null && className.trim().length() > 0
								&& id != null && id.trim().length() > 0) {							
							LayoutExtensionElement provider = layoutElements.get(id);
							if(provider == null ) {
								provider = new LayoutExtensionElement(
										bundle, className, id);
								layoutElements.put(id, provider);
							}
						}
					} catch (Exception e) {
						LibraryPlugin.getDefault().getLogger().logError(e);
					}
				}
			}
		}
	}

	public boolean hasExtension(String id) {
		return layoutElements.containsKey(id);
	}
	
	/**
	 * Creates layout extension.
	 * 
	 * @param id the extension id
	 * @return LayoutExtension
	 */
	public LayoutExtension createExtension(String id) {
		
		if ( !hasExtension(id) ) {
			return null;
		}
		
		LayoutExtensionElement provider = (LayoutExtensionElement) layoutElements.get(id);
		try {
			Class clazz = provider.bundle.loadClass(provider.className);
			return (LayoutExtension) clazz.newInstance();
		} catch (Exception e) {
			LibraryPlugin.getDefault().getLogger().logError(e);
		}
		
		return null;
	}

	private class LayoutExtensionElement {
		Bundle bundle;
		String className;
		String id;
		private LayoutExtensionElement(Bundle bundle, String className, String id) {
			this.bundle = bundle;
			this.className = className;
			this.id = id;
		}
	}
}