DiscoverableImplementationDelegate.java

/*
 * Copyright (c) 2009-2015
 * 	IT-Consulting Stephan Schloepke (http://www.schloepke.de/)
 * 	klemm software consulting Mirko Klemm (http://www.klemm-scs.com/)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package org.jbasics.discover;

import org.jbasics.checker.ContractCheck;
import org.jbasics.pattern.delegation.ReleasableDelegate;

import java.io.Serializable;

public class DiscoverableImplementationDelegate<T> implements ReleasableDelegate<T>, Serializable {
	private static final long serialVersionUID = 20120101L;
	private final Class<T> abstractClass;
	private final Class<? extends T> defaultImpl;
	private transient T instance;

	protected DiscoverableImplementationDelegate(final Class<T> abstractClass, final Class<? extends T> defaultImpl) {
		this.abstractClass = ContractCheck.mustNotBeNull(abstractClass, "abstractClass");
		this.defaultImpl = defaultImpl;
	}

	public static <T> DiscoverableImplementationDelegate<T> newInstance(final Class<T> abstractClass) {
		return new DiscoverableImplementationDelegate<T>(abstractClass, null);
	}

	public static <T> DiscoverableImplementationDelegate<T> newInstance(final Class<T> abstractClass, final Class<? extends T> defaultImpl) {
		return new DiscoverableImplementationDelegate<T>(abstractClass, defaultImpl);
	}

	public T delegate() {
		if (this.instance == null) {
			final Class<? extends T> temp = ServiceClassDiscovery.discoverImplementation(this.abstractClass, this.defaultImpl);
			if (temp == null) {
				throw new RuntimeException("Cannot find an implementation for the abstract class " + this.abstractClass.getName()); //$NON-NLS-1$
			}
			try {
				this.instance = temp.newInstance();
			} catch (final InstantiationException e) {
				throw new RuntimeException("Cannot instantiate implmentation " + temp.getName(), e); //$NON-NLS-1$
			} catch (final IllegalAccessException e) {
				throw new RuntimeException("Cannot instantiate implmentation " + temp.getName(), e); //$NON-NLS-1$
			}
		}
		return this.instance;
	}

	public boolean release() {
		this.instance = null;
		return false;
	}
}