message.java

pastry的java实现的2.0b版

/*************************************************************************

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are
met:

- Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.

- Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.

- Neither  the name  of Rice  University (RICE) nor  the names  of its
contributors may be  used to endorse or promote  products derived from
this software without specific prior written permission.

This software is provided by RICE and the contributors on an "as is"
basis, without any representations or warranties of any kind, express
or implied including, but not limited to, representations or
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particular purpose. In no event shall RICE or contributors be liable
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consequential damages (including, but not limited to, procurement of
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business interruption) however caused and on any theory of liability,
whether in contract, strict liability, or tort (including negligence
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if advised of the possibility of such damage.

********************************************************************************/
package rice.pastry.messaging;

import java.io.*;
import java.util.*;

import rice.pastry.*;

/**
 * This is an abstract implementation of a message object.
 *
 * @version $Id: Message.java 3274 2006-05-15 16:17:47Z jeffh $
 * @author Andrew Ladd
 * @author Sitaram Iyer
 */

public abstract class Message implements Serializable, rice.p2p.commonapi.Message {

  private int destination;

  private NodeHandle sender;

  /**
   * Potentially needed for reverse compatability with serialization? Remove
   * this when move to byte-level protocol.
   */
  private boolean priority;

  private byte priorityLevel = DEFAULT_PRIORITY_LEVEL;

  private transient Date theStamp;
  private final static long serialVersionUID = 8921944904321235696L;

  /**
   * DESCRIBE THE FIELD
   */
  public final static int DEFAULT_PRIORITY_LEVEL = 5;

  /**
   * Constructor.
   *
   * @param dest the destination.
   */

  public Message(int dest) {
    this(dest, null);
  }

  /**
   * Constructor.
   *
   * @param dest the destination.
   * @param timestamp the timestamp
   */

  public Message(int dest, Date timestamp) {
    destination = dest;
    this.theStamp = timestamp;
    sender = null;
    priority = false;
  }

  /**
   * Gets the address of message receiver that the message is for.
   *
   * @return the destination id.
   */
  public int getDestination() {
    return destination;
  }

  /**
   * Gets the timestamp of the message, if it exists.
   *
   * @return a timestamp or null if the sender did not specify one.
   */
  public Date getDate() {
    return theStamp;
  }

  /**
   * Get sender Id.
   *
   * @return the immediate sender's NodeId.
   */
  public Id getSenderId() {
    if (sender == null) {
      return null;
    }
    return sender.getNodeId();
  }

  /**
   * Get sender.
   *
   * @return the immediate sender's NodeId.
   */
  public NodeHandle getSender() {
    return sender;
  }

  /**
   * Get priority
   *
   * @return the priority of this message.
   */
  public byte getPriority() {
    return priorityLevel;
  }

  /**
   * Set sender Id. Called by NodeHandle just before dispatch, so that this Id
   * is guaranteed to belong to the immediate sender.
   *
   * @param nh The new Sender value
   */
  public void setSender(NodeHandle nh) {
    sender = nh;
  }

  /**
   * Set priority.
   *
   * @param prio The new Priority value
   */
  protected void setPriority(byte prio) {
    priorityLevel = prio;
  }

  /**
   * If the message has no timestamp, this will stamp the message.
   *
   * @param time the timestamp.
   * @return true if the message was stamped, false if the message already had a
   *      timestamp.
   */
  public boolean stamp(Date time) {
    if (theStamp.equals(null)) {
      theStamp = time;
      return true;
    } else {
      return false;
    }
  }
}