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Java Deferred/Promise library similar to JQuery.
There is a newer version: 1.2.6
/*
 * Copyright 2013 Ray Tsang
 * 
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *   http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jdeferred.impl;

import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;

import org.jdeferred.AlwaysCallback;
import org.jdeferred.DoneCallback;
import org.jdeferred.DoneFilter;
import org.jdeferred.DonePipe;
import org.jdeferred.FailCallback;
import org.jdeferred.FailFilter;
import org.jdeferred.FailPipe;
import org.jdeferred.ProgressCallback;
import org.jdeferred.ProgressFilter;
import org.jdeferred.ProgressPipe;
import org.jdeferred.Promise;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 *
 * @see Promise
 * @author Ray Tsang
 *
 */
public abstract class AbstractPromise implements Promise {
	final protected Logger log = LoggerFactory.getLogger(AbstractPromise.class);
	
	protected volatile State state = State.PENDING;

	protected final List> doneCallbacks = new CopyOnWriteArrayList>();
	protected final List> failCallbacks = new CopyOnWriteArrayList>();
	protected final List> progressCallbacks = new CopyOnWriteArrayList>();
	protected final List> alwaysCallbacks = new CopyOnWriteArrayList>();
	
	protected D resolveResult;
	protected F rejectResult;

	@Override
	public State state() {
		return state;
	}
	
	@Override
	public Promise done(DoneCallback callback) {
		synchronized (this) {
			doneCallbacks.add(callback);
			if (isResolved()) triggerDone(callback, resolveResult);
		}
		return this;
	}

	@Override
	public Promise fail(FailCallback callback) {
		synchronized (this) {
			failCallbacks.add(callback);
			if (isRejected()) triggerFail(callback, rejectResult);
		}
		return this;
	}
	
	@Override
	public Promise always(AlwaysCallback callback) {
		synchronized (this) {
			alwaysCallbacks.add(callback);
			if (!isPending()) triggerAlways(callback, state, resolveResult, rejectResult);
		}
		return this;
	}
	
	protected void triggerDone(D resolved) {
		for (DoneCallback callback : doneCallbacks) {
			try {
				triggerDone(callback, resolved);
			} catch (Exception e) {
				log.error("an uncaught exception occured in a DoneCallback", e);
			}
		}
	}
	
	protected void triggerDone(DoneCallback callback, D resolved) {
		callback.onDone(resolved);
	}
	
	protected void triggerFail(F rejected) {
		for (FailCallback callback : failCallbacks) {
			try {
				triggerFail(callback, rejected);
			} catch (Exception e) {
				log.error("an uncaught exception occured in a FailCallback", e);
			}
		}
	}
	
	protected void triggerFail(FailCallback callback, F rejected) {
		callback.onFail(rejected);
	}
	
	protected void triggerProgress(P progress) {
		for (ProgressCallback callback : progressCallbacks) {
			try {
				triggerProgress(callback, progress);
			} catch (Exception e) {
				log.error("an uncaught exception occured in a ProgressCallback", e);
			}
		}
	}
	
	protected void triggerProgress(ProgressCallback
 callback, P progress) {
		callback.onProgress(progress);
	}
	
	protected void triggerAlways(State state, D resolve, F reject) {
		for (AlwaysCallback callback : alwaysCallbacks) {
			try {
				triggerAlways(callback, state, resolve, reject);
			} catch (Exception e) {
				log.error("an uncaught exception occured in a AlwaysCallback", e);
			}
		}
		
		synchronized (this) {
			this.notifyAll();
		}
	}
	
	protected void triggerAlways(AlwaysCallback callback, State state, D resolve, F reject) {
		callback.onAlways(state, resolve, reject);
	}

	@Override
	public Promise progress(ProgressCallback
 callback) {
		progressCallbacks.add(callback);
		return this;
	}

	@Override
	public Promise then(DoneCallback callback) {
		return done(callback);
	}

	@Override
	public Promise then(DoneCallback doneCallback, FailCallback failCallback) {
		done(doneCallback);
		fail(failCallback);
		return this;
	}

	@Override
	public Promise then(DoneCallback doneCallback, FailCallback failCallback,
			ProgressCallback progressCallback) {
		done(doneCallback);
		fail(failCallback);
		progress(progressCallback);
		return this;
	}
	
	@Override
	public  Promise then(
			DoneFilter doneFilter) {
		return new FilteredPromise(this, doneFilter, null, null);
	}
	
	@Override
	public  Promise then(
			DoneFilter doneFilter, FailFilter failFilter) {
		return new FilteredPromise(this, doneFilter, failFilter, null);
	}
	
	@Override
	public  Promise then(
			DoneFilter doneFilter, FailFilter failFilter,
			ProgressFilter progressFilter) {
		return new FilteredPromise(this, doneFilter, failFilter, progressFilter);
	}
	
	@Override
	public  Promise then(
			DonePipe doneFilter) {
		return new PipedPromise(this, doneFilter, null, null);
	}

	@Override
	public  Promise then(
			DonePipe doneFilter,
			FailPipe failFilter) {
		return new PipedPromise(this, doneFilter, failFilter, null);
	}

	@Override
	public  Promise then(
			DonePipe doneFilter,
			FailPipe failFilter,
			ProgressPipe progressFilter) {
		return new PipedPromise(this, doneFilter, failFilter, progressFilter);
	}
	
	@Override
	public boolean isPending() {
		return state == State.PENDING;
	}

	@Override
	public boolean isResolved() {
		return state == State.RESOLVED;
	}

	@Override
	public boolean isRejected() {
		return state == State.REJECTED;
	}
	
	public void waitSafely() throws InterruptedException {
		waitSafely(-1);
	}
	public void waitSafely(long timeout) throws InterruptedException {
		final long startTime = System.currentTimeMillis();
		synchronized (this) {
			while (this.isPending()) {
				try {
					if (timeout <= 0) {
						wait();
					} else {
						final long elapsed = (System.currentTimeMillis() - startTime);
					    final long waitTime = timeout - elapsed;
						wait(waitTime);
					}
				} catch (InterruptedException e) {
					Thread.currentThread().interrupt();
					throw e;
				}
				
				if (timeout > 0 && ((System.currentTimeMillis() - startTime) >= timeout)) {
					return;
				} else {
					continue; // keep looping
				}
			}
		}
	}
}