byte array for transmission using UDP packets

In the lab notes this week I asked for a method of packing and unpacking arbitrary java primatives 
into a byte array for transmission using UDP packets. 
 The ByteArrayOutputStream and the DataOutputStream are your friends in these cases:


                // send 4 integers in a UDP packet

               ByteArrayOutputStream baos = new ByteArrayOutputStream( MAX_PACKET_SIZE );
               DataOutputStream out = new DataOutputStream( baos );

               // now send a sequenc of 4 integers ... "2, 4, 6 8"

               byte [] data = null;
               try {
                       out.writeInt(  2 );
                       out.writeInt(  4 );
                       out.writeInt(  6 );
                       out.writeInt(  8 );
                       out.flush();
                       data = baos.toByteArray();
               } catch ( Exception e ) {
                       usage( "Error formatting data: " + e.getMessage() );
               }

               // now data (a byte [] ) is ready to send

Similarly, at the receiving end, ue ByteArrayInputStream in conjunction with a DataInputStream:

               byte [] data = new byte[ MAX_PACKET_SIZE ];
               DatagramSocket s = null;

               try {
                       s = new DatagramSocket( port );
               } catch ( Exception e ) {
                       usage( "Error opening receiving socket: " + e.getMessage() );
               }

               // loop reading datagrams

               while( true ) {
                       try {
                               DatagramPacket p = new DatagramPacket( data, data.length );
                               s.receive(p);

                               // now decode the data in the byte array

                               ByteArrayInputStream bais = new ByteArrayInputStream( data );
                               DataInputStream in = new DataInputStream( bais );

                               int i1 = in.readInt();
                               int i2 = in.readInt();
                               int i3 = in.readInt();
                               int i4 = in.readInt();

                               // output result to console

                               System.out.println( "Received datagram with data "
                                                                       +i1+" "+i2+" "+i3+" "+i4 );

                       } catch ( Exception e ) {
                               usage( "Error reading datagram: " + e.getMessage() );
                       }
               }


We can avoid fiddling with the bits this way.

 

Full code source