Using ObjectInputStream and ObjectOutputStream between client and server process

Question

I develop a client-server java application and I used ObjectOutputStream and ObjectInputStream to send and receive data between client and server process. I need to send Array or object or primitive data but the problem appears when I use ObjectOutputStream and ObjectInputStream to send and receive primitive values ( writeDouble(), readDouble(), writeUTF(), readUTF() ) . the program suspended and stopped working. why, what is the problem?

these are a fragments of my program

// client program

    ObjectOutputStream toServer;
    ObjectInputStream fromServer;

// Establish connection with the server
            Socket socket = new Socket(host, 7000);

            // Create an output stream to the server
            toServer = new ObjectOutputStream(socket.getOutputStream());
            fromServer = new ObjectInputStream(socket.getInputStream());

double num1 = Double.parseDouble(jtf1.getText().trim());
                    double num2 = Double.parseDouble(jtf2.getText().trim());
                    try {
                        toServer.writeUTF("multiply");
                        toServer.writeDouble(num1);
                        toServer.writeDouble(num2);
                        double result = fromServer.readDouble();
                        res.setText(String.valueOf(result));
                    } catch (IOException ex) {
                        System.err.println(ex);
                    }

// server program

private ObjectOutputStream outputToClient;
    private ObjectInputStream inputFromClient;

// Create a server socket
            ServerSocket serverSocket = new ServerSocket(7000);

while (true) {
                // Listen for a new connection request
                Socket socket = serverSocket.accept();
                System.out.println("connect ");
                outputToClient = new ObjectOutputStream(socket.getOutputStream());
                // Create an input stream from the socket
                inputFromClient =
                        new ObjectInputStream(socket.getInputStream());
                while(true)  {
                // Read from input
                String command = inputFromClient.readUTF();
                System.out.println("receive command");
                checkRequest(command);
                }
                // Write to the file
                //outputToFile.writeObject(object);

            }

public void checkRequest(String cmd){
        //Object o = null;
        try{
        if(cmd.equals(MULTIBLY)){
            double x = inputFromClient.readDouble();
            double y = inputFromClient.readDouble();
            double result = x*y;
            outputToClient.writeDouble(result);
            System.out.println("send result");
        }else if (cmd.equals(DIVIDE)){
            int x = inputFromClient.readInt();
            int result = 1000/x;
            outputToClient.writeDouble(result);
        }
        } catch(IOException io){

        }
    }

when I change ObjectOutputstream and ObjectInputStream to DataOutputStream and DataInputStream every thing goes correctly !

Solution

You must call flush() on the stream on the client side to actually send the data (if the socket's buffer is not full). You see your program hanging because the client does not send the data, and the server is blocking, waiting for the data that will never come.