continuationmessage.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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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.*;

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

/**
 * @(#) ContinuationMessage.java This class the abstraction of a message used
 * internally by Past which serves as a continuation (for receiving the results
 * of an operation).
 *
 * @version $Id: ContinuationMessage.java 3274 2006-05-15 16:17:47Z jeffh $
 * @author Alan Mislove
 * @author Ansley Post
 * @author Peter Druschel
 */
public abstract class ContinuationMessage extends PastMessage implements Continuation {

  // the response data
  /**
   * DESCRIBE THE FIELD
   */
  protected Object response;

  // the response exception, if one is thrown
  /**
   * DESCRIBE THE FIELD
   */
  protected Exception exception;

  /**
   * DESCRIBE THE FIELD
   */
  protected byte serType;

  final static long serialVersionUID = 1321112527034107161L;

  /**
   * No response or exception.
   */
  public static byte S_EMPTY = 0;
  /**
   * Subclass handled serialization.
   */
  public static byte S_SUB = 1;
  /**
   * Java Serialized Response
   */
  public static byte S_JAVA_RESPONSE = 3;
  /**
   * Java Serialized Exception
   */
  public static byte S_JAVA_EXCEPTION = 2;

  /**
   * Constructor which takes a unique integer Id, as well as the data to be
   * stored
   *
   * @param uid The unique id
   * @param source The source handle
   * @param dest The destination address
   */
  protected ContinuationMessage(int uid, NodeHandle source, Id dest) {
    super(uid, source, dest);
  }


  /**
   * The serialization stategy is that usually the subtype will have an optimal
   * serialization strategy, but sometimes we will have to revert to java
   * serialization
   *
   * @param buf
   * @param endpoint
   * @exception IOException DESCRIBE THE EXCEPTION
   * @throws IOException
   */
  public ContinuationMessage(InputBuffer buf, Endpoint endpoint) throws IOException {
    super(buf, endpoint);
    serType = buf.readByte();
    if (serType > S_SUB) {
      deserialize(buf, endpoint);
    }
    // not empty, and not handled by the sub
  }

  /**
   * Returns the response
   *
   * @return The response
   */
  public Object getResponse() {
    return response;
  }

  /**
   * Method which builds a response for this message, using the provided object
   * as a result.
   *
   * @param o The object argument
   */
  public void receiveResult(Object o) {
    setResponse();
    response = o;
  }

  /**
   * Method which builds a response for this message, using the provided
   * exception, which was thrown
   *
   * @param e The exception argument
   */
  public void receiveException(Exception e) {
    setResponse();
//    System.out.println("ContinuationMessage.receiveException("+e+")");
//    e.printStackTrace();
    exception = e;
  }

  /**
   * 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) {
    if (exception == null) {
      c.receiveResult(response);
    } else {
      c.receiveException(exception);
    }
  }

  /**
   * @param buf
   * @param endpoint DESCRIBE THE PARAMETER
   * @throws IOException
   */
  public void deserialize(InputBuffer buf, Endpoint endpoint) throws IOException {
    byte[] array = new byte[buf.readInt()];
    buf.read(array);
    ObjectInputStream ois = new JavaDeserializer(new ByteArrayInputStream(array), endpoint);
    Object content;
    try {
      content = ois.readObject();
      if (serType == S_JAVA_RESPONSE) {
        response = content;
      } else {
        exception = (Exception) content;
      }
    } catch (ClassNotFoundException e) {
      throw new RuntimeException("Unknown class type in message - closing channel.", e);
    }
  }

  /**
   * Deprecated to cause warnings.
   *
   * @param buf DESCRIBE THE PARAMETER
   * @exception IOException DESCRIBE THE EXCEPTION
   * @deprecated use serialize(OutputBuffer buf, boolean javaSerialize)
   */
  public void serialize(OutputBuffer buf) throws IOException {
    throw new RuntimeException("Illegal call.  Must call serialize(OutputBuffer, boolean");
  }

  /**
   * If you want this class to serialize itself, set javaSerialize to true,
   * otherwise, the subclass is expected to do an optimal serializatoin
   *
   * @param buf
   * @param javaSerialize
   * @throws IOException
   */
  public void serialize(OutputBuffer buf, boolean javaSerialize) throws IOException {
//    System.out.println("ContinuationMessage<"+getClass().getName()+">.serialize("+javaSerialize+") resp:"+response+" exc:"+exception+" id:"+id+" src:"+source+" dst:"+dest);
    super.serialize(buf);

    serType = S_EMPTY;

    if (javaSerialize) {
      Object content = response;
      if (response != null) {
        serType = S_JAVA_RESPONSE;
      } else {
        serType = S_JAVA_EXCEPTION;
        content = exception;
      }

      if (content == null) {
        serType = S_EMPTY;
        buf.writeByte(serType);
      } else {
//      if (true) throw new IOException("Test");
//        System.out.println("ContinuationMessage<"+getClass().getName()+">.serialize():"+serType+" "+response+" "+exception);
        buf.writeByte(serType);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ObjectOutputStream oos = new ObjectOutputStream(baos);

        // write out object and find its length
        oos.writeObject(content);
        oos.close();

        byte[] temp = baos.toByteArray();
        buf.writeInt(temp.length);
        buf.write(temp, 0, temp.length);
      }
    } else {
      buf.writeByte(S_SUB);
    }
  }
}