Java - Listening to a socket with ObjectInputStream

Question

Ok so , i have a thread class called 'Client' every time the server accepts a connection it creates a new Client....The run method listens for messages from the client and i am useing ObjectInputStream ..

   do {            
         ObjectInputStream in = null;

        try {
            in = new ObjectInputStream(socket.getInputStream());
            String message = (String) in.readObject();
            System.out.println(message);
            }
            catch (ClassNotFoundException ex) {
                isConnected = false;
                System.out.println("Progoramming Error");
            }
            catch (IOException ex) {
                isConnected = false;
                System.out.println("Server ShutDown");
                System.exit(0);
            }
    } while(isConnected);

The Problem i have is that why do i have to create a new ObjectInputStream every time it loops...and if i close the input stream at the end of the loop and it loops again for another message i will get a error...Please some one help

Answer 1

Only create the ObjectInputStream once (outside the loop) for a client connection, then put the readObject method into the loop.

Here's a working test class:

public class TestPrg {

    public static void main(String... args) throws IOException {
        ServerListener server = new ServerListener();
        server.start();

        Socket socketToServer = new Socket("localhost", 15000);
        ObjectOutputStream outStream = new ObjectOutputStream(socketToServer.getOutputStream());

        for (int i=1; i<10; i++) {
            try {
                Thread.sleep((long) (Math.random()*3000));
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Sending object to server ...");
            outStream.writeObject("test message #"+i);
        }
        System.exit(0);

    }

    static class ServerListener extends Thread {

        private ServerSocket serverSocket;

        ServerListener() throws IOException {
            serverSocket = ServerSocketFactory.getDefault().createServerSocket(15000);
        }

        @Override
        public void run() {
            while (true) {
                try {
                    final Socket socketToClient = serverSocket.accept();
                    ClientHandler clientHandler = new ClientHandler(socketToClient);
                    clientHandler.start();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }

    static class ClientHandler extends Thread{
        private Socket socket;
        ObjectInputStream inputStream;

        ClientHandler(Socket socket) throws IOException {
            this.socket = socket;
            inputStream = new ObjectInputStream(socket.getInputStream());
        }

        @Override
        public void run() {
            while (true) {
                try {
                    Object o = inputStream.readObject();
                    System.out.println("Read object: "+o);
                } catch (IOException e) {
                    e.printStackTrace();

                } catch (ClassNotFoundException e) {
                    e.printStackTrace();
                }
            }
        }
    }

}

In this example Strings are sent trough the ObjectStream. If you get the ClassNotFoundException (http://download.oracle.com/javase/6/docs/api/java/io/ObjectInputStream.html#readObject()) and are using an independent client and server program than you might check if both the client and the server have the class of the object to send in their class paths.