RAPSingletonProvider.java

/*******************************************************************************
 * Copyright (c) 2007, 2014 compeople AG 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:
 *    compeople AG - initial API and implementation
 *******************************************************************************/
package org.eclipse.riena.internal.core.singleton;

import java.lang.reflect.Method;
import java.util.Map;
import java.util.WeakHashMap;

import org.osgi.framework.Bundle;

import org.eclipse.riena.core.singleton.ISingletonInitializer;
import org.eclipse.riena.core.singleton.SingletonFailure;
import org.eclipse.riena.core.util.Nop;
import org.eclipse.riena.core.util.RAPDetector;
import org.eclipse.riena.core.wire.Wire;

/**
 * Riena's wrapper for RAP's session based singleton provider. This wrapper
 * additionally wires a newly created singleton.
 * 
 * @since 4.0
 */
public final class RAPSingletonProvider {

	private static final boolean IS_AVAILABLE;
	private static Class<?> sessionSingletonBaseClass;
	private static Method getInstanceMethod;
	private static final Map<Object, Boolean> WIRED_RAP_SINGLETONS = new WeakHashMap<Object, Boolean>();

	private static final String SESSION_SINGLETON_BASE = "org.eclipse.rap.rwt.SessionSingletonBase"; //$NON-NLS-1$
	private static final String GET_INSTANCE = "getInstance"; //$NON-NLS-1$

	static {
		IS_AVAILABLE = RAPDetector.isRAPavailable() && loadSessionSingletonBase();
	}

	private RAPSingletonProvider() {
		Nop.reason("utility"); //$NON-NLS-1$
	}

	/**
	 * Load the RAP {@code SessionSingletonBase} class and the
	 * {@code getInstance} method as a side effect.
	 * 
	 * @return {@code true} if class and method have been found; otherwise
	 *         {@code false}
	 */
	private static boolean loadSessionSingletonBase() {
		final Bundle rapBundle = RAPDetector.getRWTBundle();
		try {
			sessionSingletonBaseClass = rapBundle.loadClass(SESSION_SINGLETON_BASE);
			getInstanceMethod = sessionSingletonBaseClass.getMethod(GET_INSTANCE, Class.class);
			return true;
		} catch (final Exception e) {
			// There seems to be no RAP available.
			return false;
		}
	}

	/**
	 * Is RAP available and could RAP's singleton creation function be located
	 * (reflection)?
	 * 
	 * @return true RAP is available and we can create RAP based singletons;
	 *         otherwise not
	 */
	public static boolean isAvailable() {
		return IS_AVAILABLE;
	}

	/**
	 * Return the requested wired RAP session singleton.
	 * 
	 * @param singletonClass
	 *            the class to create a RAP session based singleton
	 * 
	 * @return the singleton
	 */
	public static <S> S getInstance(final Class<S> singletonClass) {
		return getInstance(singletonClass, null);
	}

	/**
	 * Return the requested probably initialized and wired RAP session
	 * singleton.
	 * 
	 * @param singletonClass
	 *            the class to create a RAP session based singleton
	 * @param initializer
	 *            a optional initializer 'call back' (may be {@code null}
	 * 
	 * @return the singleton
	 */
	public static <S> S getInstance(final Class<S> singletonClass, final ISingletonInitializer<S> initializer) {
		try {
			final S rapSingleton = (S) getInstanceMethod.invoke(sessionSingletonBaseClass, singletonClass);
			synchronized (WIRED_RAP_SINGLETONS) {
				if (WIRED_RAP_SINGLETONS.put(rapSingleton, Boolean.TRUE) == null) {
					if (initializer != null) {
						initializer.init(rapSingleton);
					}
					Wire.instance(rapSingleton).andStart();
				}
			}
			return rapSingleton;
		} catch (final Exception e) {
			throw new SingletonFailure("Could not instantiate RAP controlled singleton.", e); //$NON-NLS-1$
		}
	}

}