messagequeue.java

发布/订阅系统路由重配算法,可应用于ad hoc环境

package broker;

import java.util.*;

import com.Message;

/**
 * A simple message queue based on a linked list.
 * @author parzy
 *
 */
public class MessageQueue {

	/**
	 * A queue entry to store the sender, the receiver, 
	 * and the message itself.
	 * @author parzy
	 */
	private class Entry {
		Destination sender = null;
		Destination receiver = null;
		Message message = null;
		private Entry(Destination sender, Destination receiver, Message message) {
			this.sender = sender;
			this.receiver = receiver;
			this.message = message;
			sender.isBroker();
		}
	}
	
	/**
	 * The queue based on a LinkedList.
	 */
	private LinkedList queue = new LinkedList();
	
	/**
	 * The sender of the last dequeued message.
	 */
	private Destination sender = null;
	
	/**
	 * The receiver of the last dequeued message.
	 */
	private Destination receiver = null;
	
	/**
	 * Enqueues a message with references to its sender and receiver.
	 * @param sender the sender of the message
	 * @param receiver the receiver of the message
	 * @param message the message itself
	 */
	public void enqueue(Destination sender, Destination receiver, Message message){
		queue.addLast(new Entry(sender, receiver, message));
	}

	/**
	 * Returns the queue's size.
	 * @return the queue's size
	 */
	public int size() {
		return queue.size();
	}
	
	/**
	 * Returns true if this queue contains no entries.
	 * @return true if this queue contains no entries.
	 */
	public boolean isEmpty() {
		return queue.isEmpty();
	}
	
	/**
	 * Dequeues the next message and stores references to its 
	 * sender and receiver. Use the getSender and getReceiver Method
	 * to access them. 
	 * @return the next message
	 */
	public Message dequeue() {
		Entry e;
		e = (Entry)queue.removeFirst();
		sender = e.sender;
		receiver = e.receiver;
		return e.message;
	}
	
	/**
	 * Returns the receiver of the last dequeued message.
	 * @return receiver of the last dequeues message.
	 */
	public Destination getReceiver() {
		return receiver;
	}
	
	/**
	 * Returns the sender of the last dequeued message.
	 * @return sender of the last dequeued message.
	 */
	public Destination getSender() {
		return sender;
	}
}