LinuxQuestions.org - Java - sending a 2d array over UDP

- Programming (https://www.linuxquestions.org/questions/programming-9/)

- - Java - sending a 2d array over UDP (https://www.linuxquestions.org/questions/programming-9/java-sending-a-2d-array-over-udp-865211/)

Java - sending a 2d array over UDP

I'm currently writing a program which will eventually send two 2d arrays to another machine using UDP, and then back again.

To do this I'm converting to a byte array which as far as I'm aware is the only way possible. I'm sure the problem is on the receiving program which receives like this:

Code:

DatagramSocket socket = new DatagramSocket(2000);

DatagramPacket packet = new DatagramPacket(new byte[5000] , 5000);

                                        

socket.receive(packet);

                        

ByteArrayInputStream bin = new ByteArrayInputStream(packet.getData()); 



int data = bin.read();

System.out.print(data);

obviously it is having a problem as it is trying to receive as an int, rather than an int[][], but it won't compile if I try something like:

Code:

int data[][] = bin.read();

So I'm basically I'm a bit stuck. Does anyone have any ideas as to how to send/receive an array (preferably 2d) using UDP in java. Or can point me in the right direction?

Personally, if this is anything more than a "toy program" for personal curiousity, I'd suggest looking into using RMI.

But if you want to use a UDP stream ...
... then you need some way to tell the client how much data it receives:

1. Send a fixed-length (n bytes) block, then read exactly n bytes
2. Send a byte count, first, then the data
3. Parse the stream for some "end of data" delimiter

As far as the syntax for reading your 1-D byte stream into a 2-D int array...
you basically get to use a "for" loop ;)

Hi -

About 30 seconds after I clicked "send", I found another approach: leverage Java's "Serializable" interface interface with I/O streams and sockets:

http://java.sun.com/developer/techni...s/ALT/sockets/

Code:

// Code Sample 8: SerializedObject.java 

import java.io.*;

import java.util.*;



public class SerializedObject implements Serializable {

  private int array[] = null;



  public SerializedObject() {

  }



  public void setArray(int array[]) {

    this.array = array;

  }



  public int[] getArray() {

    return array;

  }

}

Code:

// Code Sample 9: ArrayClient.java 

import java.io.*;

import java.net.*;



public class ArrayClient {

  public static void main(String argv[]) {

      ObjectOutputStream oos = null;

      ObjectInputStream ois = null;

      // two arrays

      int dataset1[] = {3, 3, 3, 3, 3, 3, 3};

      int dataset2[] = {5, 5, 5, 5, 5, 5, 5};

      try {

        // open a socket connection

        Socket socket = new Socket("YourMachineNameORipAddress", 4000);

        // open I/O streams for objects

        oos = new ObjectOutputStream(socket.getOutputStream());

        ois = new ObjectInputStream(socket.getInputStream());

        // create two serialized objects

        SerializedObject so1 = new SerializedObject();

        SerializedObject so2 = new SerializedObject();

        SerializedObject result = null;

        int outArray[] = new int[7];

        so1.setArray(dataset1);

        so2.setArray(dataset2);

        // write the objects to the server

        oos.writeObject(so1);

        oos.writeObject(so2);

        oos.flush();

        // read an object from the server

        result = (SerializedObject) ois.readObject();

        outArray = result.getArray();

        System.out.print("The new array is: ");

        // after unpacking the array, iterate through it

        for(int i=0;i<outArray.length;i++) {

          System.out.print(outArray[i] + "  ");

        }

        oos.close();

        ois.close();

      } catch(Exception e) {

        System.out.println(e.getMessage());

      }

  }

}

The same concept, of course, can easily be extended to any arbitrarily complex object - including a 2D int array :)

I just wanted to say thanks, because this is an amazing find. I was googling and trying weird code for a good couple of hours but this is awesome.

and yeah, this is an experimental program rather than any sort of real-world solution.