How to add 16 bit message sequential number to the byte array

Question

hi
iam trying to implement socket programming over UDP. Iam writing for the server side now.I need to send an image file from server to a client via a gateway so basically ive to do hand-shaking with the gateway first and then ive to send image data in a sequence of small messages with a payload of 1 KB.The data message should also include a header of 16 bit sequential number and a bit to indicate end of file.
Iam able to complete registration process(Iam not sure yet).I dnt know how to include sequential number and a bit to indicate end of file.
I would like to have your valuable ideas about how to proceed further
package udp;
import java.io.*;
import java.net.*;
import java.util.*;
public class Sender  {
    protected BufferedReader in = null;
    protected FileInputStream image=null;
    protected static boolean end_of_file=true;
/** pass arguments hostname,port,filename
* @param args
* @throws IOException
   public static void main(String[] args) throws IOException{
        DatagramSocket socket = new DatagramSocket(Integer.parseInt(args[1]));
        boolean more_messages = true;
          String str1=null;
            * gateway registration
            try{
                 //send string to emulator
                String str="%%%GatewayRegistration SENDER test delay 10 drop 0 dupl 0 bandwidth 1000000";
                byte[] buff=str.getBytes();
                InetAddress emulator_address = InetAddress.getByName(args[0]);
                DatagramPacket packet = new DatagramPacket(buff, buff.length,emulator_address,Integer.parseInt(args[0]));
                socket.send(packet);
                    // figure out response
                byte[] buf = new byte[1024];
                DatagramPacket recpack=new DatagramPacket(buf,buf.length);
                socket.receive(recpack);
               // socket.setSoTimeout(10000);
                String str2=str1.valueOf(new String(recpack.getData()));
                if(socket.equals(null))
                     System.out.println("no acknowledgement from the emulator");
                    socket.close();
                else if(str2=="%%%GatewayConfirmation")
                //     String str1=null;
                     System.out.println("rec message"+str2);
                else
                     System.out.println("not a valid message from emulator");
                     socket.close();
            catch (IOException e) {
                e.printStackTrace();
                  end_of_file = false;
     /**create a packet with a payload of 1     KB and header of 16 bit sequential number and a bit to indicate end of file
  while(end_of_file!=false)
      String ack="y";
      String seqnum=
       File file = new File(args[2]);                               
                InputStream is = new FileInputStream(file);                 
        socket.close();
  private byte[] byteArray(InputStream in) throws IOException {
         byte[] readBytes = new byte[1024]; // make a byte array with a length equal to the number of bytes in the stream
      try{
         in.read(readBytes);  // dump all the bytes in the stream into the array
        catch(IOException e)
             e.printStackTrace();
        return readBytes;
  

Answer 1

HI Rolf.k.
Thank you for the small program it was helpfull.
You got right about that proberly there  will be conflict with some spurios data, I can already detect that when writing the data to a spreadsheet file.
I writes the data in such a way, that in each line there will be a date, a timestamp, a tab and a timestamp at the end. That means two columns.
When i set given samplerate up, that controls the rate of the data outflow from the device, (1,56 Hz - 200 Hz),   the data file that i write to , looks unorderet.
 i get more than one timestamp and severel datavalues in every line and so on down the spreadsheet file.
Now the question is: Could it be that the function that writes the data to the file,  can't handle the speed of the dataflow in such a way that the time stamp cant follow with the data flowspeed. so i'm trying to set the timestamp to be  with fractions of the seconds by adding the unit (<digit>) in the timestamp icon but its not working. Meaby when i take the fractions off a second within the timestamp i can get every timestamp with its right data value. Am i in deeb water or what do You mean!??
AAttached Pics part of program and a logfile over data written to file
regards
Zamzam
HFZ
Attachments:
DataFlowWR.JPG ‏159 KB
Datalogfile.JPG ‏386 KB