Java套接字未向服务器发送消息

Question

I have the following client socket for sending a string to the server. The server is not getting message. What could be the prob;em?

public void startClient() throws IOException {

    Socket socket = null;
    PrintWriter out = null;
    BufferedReader in = null;
    InetAddress host = null;
    BufferedReader stdIn = null;

    try {
        host = InetAddress.getByName("172.16.2.97");
        socket = new Socket(host, 52000);

        out = new PrintWriter(socket.getOutputStream(), true);
        in = new BufferedReader(new InputStreamReader(socket.getInputStream()));

        stdIn = new BufferedReader(new InputStreamReader(System.in));
        String fromServer;
        String fromUser = null;
        //ClientHelper.unpackISO();
        fromUser = ClientHelper.createISO();
        if (fromUser != null) {
            //System.out.println("Client - " + fromUser);
            out.write(fromUser);
            System.out.println("Sent message");
        }


        while ((fromServer = in.readLine()) != null) {
            System.out.println("Server - " + fromServer);
            if (fromUser != null) {
                //System.out.println("Client - " + fromUser);
                out.println(fromUser);
            }
        }
    } catch (ISOException ex) {
        Logger.getLogger(ClientDemo.class.getName()).log(Level.SEVERE, null, ex);
    } catch (UnknownHostException e) {
        System.err.println("Cannot find the host: " + host.getHostName());
        System.exit(1);
    } catch (IOException e) {
        System.err.println("Couldn't read/write from the connection: " +            e.getMessage());
        System.exit(1);
    } finally { //Make sure we always clean up
        out.close();
        in.close();
        stdIn.close();
        socket.close();
    }
}

The method ClientHelper.createISO() return a string which is supposed to be sent to the server. Unfortunately the server is not getting any string. Could the problem be proxy settings. If so how can solve it. Or is it another problem with my code? What is the problem with my code?

Answer 1

You must flush() the stream after writing to it. Sockets buffer until you get a full packet otherwise

Answer 2

Check the 5th line below, you need to flush your output stream. Otherwise server will not get any packet and you will stuck on your first in.readLine() because its blocking.

    fromUser = ClientHelper.createISO();
    if (fromUser != null) {
        //System.out.println("Client - " + fromUser);
        out.write(fromUser);
        out.flush(); // FLUSH IT HERE, packet wont be sent until you flush your stream
        System.out.println("Sent message");
    }

Also add flush after your out.write(fromUser) inside the loop.