Source code: JObjectFormat.java

package nl.west.aaa;

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

public class JObjectFormat
    implements RecordFormat
{

    /**
     * Magic object is used to quoickly identify the stream.
     * A message object may be of greater length.
     */
    private static Object magicObject=new String("JObjectFormat:1234567");

    /**
     * Write out the Message to the OutputStream.
     */
    private void writeMessage(Message msg,OutputStream out)
        throws IOException
    {
        ObjectOutputStream os=new ObjectOutputStream(out);
        os.writeObject(magicObject);
        os.writeInt(msg.getMessageType());
        os.writeObject(msg.getAttributes());
        //os.writeObject(msg);
    }

    public byte[] encodeMessage(Message msg)
    {
        try
        {
           ByteArrayOutputStream out=new ByteArrayOutputStream();
           writeMessage(msg,out);
           return out.toByteArray();
        }
        catch (IOException e)
        {
            return null;
        }
    }
    

    /**
     * Read a Message from the InputStream.
     * The stream should be tested as using the JObjectFormat
     * record format with checkHeader().
     * The read message is returned.
     * If no message is found null is returned.
     */
    public Message decodeMessage(InputStream in,Identifier from)
        throws IOException
    {
        // first check for the magic object
        boolean result=false;
        ObjectInputStream os=null;
        try
        {
            // mark current position in stream
            in.mark(((String)magicObject).length()+20);
            // make an objectstream
            os=new ObjectInputStream(in);
            // read magic object
            Object o=os.readObject();
            // test magic object
            result=o.equals(magicObject);
        }
        catch (IOException e)
        {
            result=false; // not neccesary
        }
        catch (ClassNotFoundException e)
        {
            result=false; // not neccesary
        }
        if(!result)
        {
            // reset stream to orriginal position
            // is in seporate try to execute even with exceptions
            try 
            {    
                in.reset();
            }
            catch(IOException e)
            {
                // stream may be corrupt
            }
            return null;
        }
        // go on reading the message
        Message msg=null;
        try
        {
            // read the messagetype
            int msgType=os.readInt();
            Hashtable attrs=(Hashtable)os.readObject();
            // read Message object
/*            Object o=os.readObject();
            if(!(o instanceof Message))
            {
                // throw some exception
                System.err.println("JObjectFormat.decodeMessage(): object is not a message");
            }
            msg=(Message)o;*/
            msg=new Message(msgType,attrs);
            msg.sender=from;
        }
        catch (ClassNotFoundException e)
        {
            msg=null;
            e.printStackTrace(System.err);
            // throw some exception
        }
        return msg;
    }

    public Message decodeMessage(byte[] data,Identifier from)
    {
// TODO: implement (put data in a stream and read it)    
throw new RuntimeException("NOT YET IMPLEMENTED");    
    }

}