cachemessage.java

pastry的java实现的2.0b版

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

"FreePastry" Peer-to-Peer Application Development Substrate 

Copyright 2002, Rice University. All rights reserved.

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- Redistributions in binary form must reproduce the above copyright
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- Neither  the name  of Rice  University (RICE) nor  the names  of its
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This software is provided by RICE and the contributors on an "as is"
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********************************************************************************/

package rice.p2p.past.messaging;

import java.io.IOException;

import rice.*;
import rice.environment.Environment;
import rice.p2p.commonapi.*;
import rice.p2p.commonapi.rawserialization.*;
import rice.p2p.past.*;
import rice.p2p.past.rawserialization.*;

/**
 * @(#) CacheMessage.java This class represents message which pushes an object
 * forward one hop in order to be cached.
 *
 * @version $Id: CacheMessage.java 3274 2006-05-15 16:17:47Z jeffh $
 * @author Alan Mislove
 * @author Ansley Post
 * @author Peter Druschel
 */
public class CacheMessage extends PastMessage {

  // the content to be cached
  /**
   * DESCRIBE THE FIELD
   */
  protected RawPastContent content;

  /**
   * DESCRIBE THE FIELD
   */
  public final static short TYPE = 1;

  /**
   * Constructor which takes a unique integer Id and the local id
   *
   * @param uid The unique id
   * @param content DESCRIBE THE PARAMETER
   * @param source DESCRIBE THE PARAMETER
   * @param dest DESCRIBE THE PARAMETER
   */
  public CacheMessage(int uid, PastContent content, NodeHandle source, Id dest) {
    this(uid, content instanceof RawPastContent ? (RawPastContent) content : new JavaSerializedPastContent(content), source, dest);
  }

  /**
   * Constructor for CacheMessage.
   *
   * @param uid DESCRIBE THE PARAMETER
   * @param content DESCRIBE THE PARAMETER
   * @param source DESCRIBE THE PARAMETER
   * @param dest DESCRIBE THE PARAMETER
   */
  public CacheMessage(int uid, RawPastContent content, NodeHandle source, Id dest) {
    super(uid, source, dest);

    this.content = content;
  }

  /**
   * Constructor for CacheMessage.
   *
   * @param buf DESCRIBE THE PARAMETER
   * @param endpoint DESCRIBE THE PARAMETER
   * @param pcd DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  private CacheMessage(InputBuffer buf, Endpoint endpoint, PastContentDeserializer pcd) throws IOException {
    super(buf, endpoint);
    // this can be done lazilly to be more efficient, must cache remaining bits, endpoint, cd, and implement own InputBuffer
    short contentType = buf.readShort();
    if (contentType == 0) {
      content = new JavaSerializedPastContent(pcd.deserializePastContent(buf, endpoint, contentType));
    } else {
      content = (RawPastContent) pcd.deserializePastContent(buf, endpoint, contentType);
    }
  }

  /**
   * Method which returns the content
   *
   * @return The content
   */
  public PastContent getContent() {
//  if (content == null)
    if (content.getType() == 0) {
      return ((JavaSerializedPastContent) content).getContent();
    }
    return content;
  }

  /**
   * Raw Serialization **************************************
   *
   * @return The Type value
   */
  public short getType() {
    return TYPE;
  }

  /**
   * Method by which this message is supposed to return it's response.
   *
   * @param c The continuation to return the reponse to.
   * @param env DESCRIBE THE PARAMETER
   * @param instance DESCRIBE THE PARAMETER
   */
  public void returnResponse(Continuation c, Environment env, String instance) {
    throw new RuntimeException("ERROR: returnResponse should not be called on cacheMessage!");
  }

  /**
   * Returns a string representation of this message
   *
   * @return A string representing this message
   */
  public String toString() {
    return "[CacheMessage for " + content + "]";
  }

  /**
   * DESCRIBE THE METHOD
   *
   * @param buf DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public void serialize(OutputBuffer buf) throws IOException {
    buf.writeByte((byte) 0);
    // version
    super.serialize(buf);
    buf.writeShort(content.getType());
    content.serialize(buf);
  }

  /**
   * DESCRIBE THE METHOD
   *
   * @param buf DESCRIBE THE PARAMETER
   * @param endpoint DESCRIBE THE PARAMETER
   * @param pcd DESCRIBE THE PARAMETER
   * @return DESCRIBE THE RETURN VALUE
   * @exception IOException DESCRIBE THE EXCEPTION
   */
  public static CacheMessage build(InputBuffer buf, Endpoint endpoint, PastContentDeserializer pcd) throws IOException {
    byte version = buf.readByte();
    switch (version) {
      case 0:
        return new CacheMessage(buf, endpoint, pcd);
      default:
        throw new IOException("Unknown Version: " + version);
    }
  }

}