CODEWITHSUNDEEP
javaserversocket
s840109mm
s840109mm

Reputation: 43

Java socket reading and writeing hex code

I'm working on a project and i want to comunicate with a device. I made a socket connection with the device, the connection works but the device is sending me the message: 0xd7d0 and i have to write that message back. It's a keep alive message. I'm haveing trouble reading and sending back that message. here's the code i've writen so far:

package Server;

import java.io.IOException;
import java.net.ServerSocket;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Server {

    public static ServerSocket serverSocket;

    public static void main (String [] args) {
        try {
            serverSocket = new ServerSocket(1234);

            while (true) {
                ServerThread serverThread = new ServerThread(serverSocket.accept());
                serverThread.start();
            }
        } catch (IOException ex) {
            Logger.getLogger(Server.class.getName()).log(Level.SEVERE, null, ex);
        }

    }
}

package Server;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;
import java.nio.ByteBuffer;
import java.util.logging.Level;
import java.util.logging.Logger;

public class ServerThread extends Thread {

    public Socket socket;
    public BufferedReader in;
    public PrintWriter out; 
    public ByteBuffer buf;
    int count;


    public ServerThread (Socket socket) {
        try {
            this.socket = socket;
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new PrintWriter(socket.getOutputStream(), true);
        } catch (IOException ex) {
            Logger.getLogger(ServerThread.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    @Override
    public void run() {
        while (true) {
            try {
                count = in.read();
                buf = ByteBuffer.allocate(100);
                buf.put((byte) count);
                buf.flip();
                out.println(buf);

                String line = in.readLine();
                System.out.println(line);




            } catch (IOException ex) {
                Logger.getLogger(ServerThread.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    }
}

Can anyone tell me what i am doing wrong?

Upvotes: 1

Views: 2121

Answers (2)

Alexei Kaigorodov
Alexei Kaigorodov

Reputation: 13535

Your mistake is that you mix different styles of network data exchange. First, what format are messages in? Are they characters in some encoding, or some binary data? In the first case, you should not use Buffer to read message in, but read and write using in and out character streams you created already. In the second case, you have 2 options: read and write with socket and byte streams, or with channels from java.nio.channels and Buffers. To write back a message in a buffer, you can use 

     buf.flip();
     buffer.position(buffer.limit());

Upvotes: 0

Brian Agnew
Brian Agnew

Reputation: 272367

This 

while (true) {
    ServerThread serverThread = new ServerThread(serverSocket.accept());
    serverThread.start();
}

doesn't look right. You're looping and creating a new thread repeatedly (which will consume resources and create an enormous number of threads). You should simply create that thread once. If your program is doing nothing else then a new thread may be superfluous.

Upvotes: 1

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