Sending an ArrayList over UDP, as a byte array.

[eggmanpete]

Hi guys, I'm not exactly sure what I am doing, so I'll need a bit of help with this one.

I have a server sending a packet with an ArrayList over a UDP socket by converting it to a byte [].
then the client reads the packet and converts the byte [] back to an ArrayList.

The error I'm getting is this...

14-Feb-2009 17:34:35 UI.input$1 sendUpdate
SEVERE: null
java.io.StreamCorruptedException: invalid stream header: EFBFBDEF
        at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:783)
        at java.io.ObjectInputStream.<init>(ObjectInputStream.java:280)
        at networkUDP.udpclient.udpsend(udpclient.java:48)
        at UI.input$1.sendUpdate(input.java:30)

CLIENT:

                        //prepare for intercepting a reply from server
			// this reply will contain the updated game board
			DatagramPacket receivePacket = new DatagramPacket(receiveByte,
				receiveByte.length);
			udpSocket.receive(receivePacket);
			//extract data from received packet and print it
			String incomingWord = new String(receivePacket.getData());
			System.out.println(incomingWord);
			udpSocket.close();
			byte [] incomingBytes = incomingWord.getBytes();

			// de-serialize
			//ByteArrayOutputStream abcd = new ByteArrayOutputStream();
			ByteArrayInputStream bais = new ByteArrayInputStream(incomingBytes);

			ObjectInputStream ois = new ObjectInputStream(bais); //TODO: MAKE INTO incomingWord

			// output board
			ArrayList board = (ArrayList) ois.readObject();
			ois.close();
			int x =0;
			while (x != board.size()) {
				System.out.println(board.get(x));
				x++;
			}
			x=0;

SERVER:

                        finishBoard = board.updateBoard(col, row);
			//TODO: serialize the array list here and sent it
			// then read the serialsed object back at the client
			ByteArrayOutputStream fos = new ByteArrayOutputStream();
			ObjectOutputStream oos = new ObjectOutputStream(fos);
			oos.writeObject(finishBoard);
			oos.close();

			// end serialization
			sendByte = fos.toByteArray();

			DatagramPacket sendPacket = new DatagramPacket(
				sendByte, sendByte.length, IP, port);
			serverSocket.send(sendPacket);

Thanks for any help :confused:

[toadaly]

The error you're getting indicates the stream is not a serialized object. Are you sure your server is the only thing using that group address and port? If so, is it possible your ArrayList is being modified by another thread while it's being serialized?

[eggmanpete]

I'm completely new to serialization.
Is it the ByteArrayOutputStream or the ObjectOutputStream that does the serialization?

[toadaly]

The ObjectOutputStream does the serialization. The ByteArrayOutputStream is just an intermediary that converts an output stream to a byte array.

Also, it occurs to me that whatever Objects you're putting into the ArrayList might not be serializable. Are you sure they are?

Try an experiment where you send just an empty new ArrayList, and verify that works ok (it should). Once you've convinced yourself the bug really is somewhere in your own code, you can work backwards to find it.

[eggmanpete]

Right, i have somehow fixed that error. Can't remember how but I'll post my code in a bit.

Now I have a new problem.

error is:

java.io.StreamCorruptedException: invalid type code: 00
at java.io.ObjectInputStream.readObject(....

any idea?

at least I'm getting somewhere :)

[Fubarable]

Just curious, why are you using UDP datagrams to send the data and not the more reliable (though slower) TCP protocol?

[eggmanpete]

Just curious, why are you using UDP datagrams to send the data and not the more reliable (though slower) TCP protocol?

I'm working on a project which requires that I use both protocols :)

Right the new problem is with the following code...:

System.out.println((ArrayList) ois.readObject());

prints the ArrayList successfully, but when I do:

ArrayList board = new ArrayList();
board = (ArrayList) ois.readObject();

It kicks up error:

15-Feb-2009 21:36:00 UI.input$1 sendUpdate
SEVERE: null
java.io.StreamCorruptedException: invalid type code: 00
 
        at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1356)

Any idea? Cheers

[eggmanpete]

I figured it out.

ois.readObject();

seems to empty the ois and as I was System.outing it, i couldn't add it to the array.

Cheers for the help guys :)

[lathapon]

I am getting the same issue "java.io.StreamCorruptedException: invalid type code: 00" in my JBOSS server version 4.0.4 GA. with jdk1.5. Please let me know how to correct this. I am returning arraylist which is serialized

[Fubarable]

lathapon: it's probably best for you to ask your new question in its own thread and in that thread link to this one. It will increase your chances of getting help.