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A Java NATS client.
There is a newer version: 0.5.Beta4
/*
 *   Copyright (c) 2013 Mike Heath.  All rights reserved.
 *
 *   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 nats.client;

import nats.NatsInterruptedException;

import java.util.NoSuchElementException;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;

/**
 * A {@link MessageIterator} that is backed by a {@link LinkedBlockingQueue}.
 *
 * @author Mike Heath 
 */
public class BlockingQueueMessageIterator implements MessageIterator, MessageHandler {

	private static final Message CLOSED = new DefaultMessage(null, null, null, false);

	private final BlockingQueue queue = new LinkedBlockingQueue<>();
	private volatile boolean closed = false;

	@Override
	public void close() {
		if (closed) {
			return;
		}
		closed = true;
		onMessage(CLOSED);
	}

	@Override
	public boolean hasNext() {
		return queue.peek() != CLOSED;
	}

	@Override
	public Message next() throws NatsClosedException, NatsInterruptedException, NoSuchElementException {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		try {
			final Message message = queue.take();
			if (message == CLOSED) {
				throw new NatsClosedException("Iterator was closed.");
			}
			return message;
		} catch (InterruptedException e) {
			throw new NatsInterruptedException(e);
		}
	}

	@Override
	public Message next(long timeout, TimeUnit unit) throws NatsClosedException, NatsInterruptedException, NoSuchElementException {
		if (!hasNext()) {
			throw new NoSuchElementException();
		}
		try {
			final Message message = queue.poll(timeout, unit);
			if (message == CLOSED) {
				throw new NatsClosedException("Iterator was closed.");
			}
			return message;
		} catch (InterruptedException e) {
			throw new NatsInterruptedException(e);
		}
	}

	@Override
	public void remove() throws UnsupportedOperationException {
		throw new UnsupportedOperationException("You can't remove a message that has been published. Nice try though.");
	}

	@Override
	public void onMessage(Message message) {
		try {
			queue.put(message);
		} catch (InterruptedException e) {
			throw new NatsInterruptedException(e);
		}
	}
}