Socket problem - readline won't work properly

Question

I try to code a client and server connection using socket. The problem is my client can\'t read the response from the server (it hangs on the readline).

Here is some

Answer 1

OK, I made several editing in the code and now it run nicely :

The server :

    try {
        // Create the server socket.
        portNumber = Integer.parseInt(myParam.get("socket.portNumber"));
        mainSocket = new ServerSocket(portNumber);

    } catch (IOException ioe) {
        System.out.println("Error Message : " + ioe.getMessage());
    }

    // Accept connections    
    try {
        clientSocket = mainSocket.accept();
    } catch (IOException ioe) {
        System.out.println("Error Message : " + ioe.getMessage());
    }
    BufferedReader in = null;
    PrintWriter out = null;

    while (true) {
        try {
            in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
            out = new PrintWriter(new OutputStreamWriter(clientSocket.getOutputStream()));
            //Read The Message
            **StringBuffer buffer = new StringBuffer();
            while (true) {
                int ch = in.read();
                if ((ch < 0) || (ch == '\n')) {
                    break;
                }
                buffer.append((char) ch);
            }
            String clientRequest = buffer.toString();**

            SocketServerThread st = new SocketServerThread(clientRequest, out);
            st.start();
        } catch (IOException ioe) {
            System.out.println("Can't accept connection. Error message :" + ioe.getMessage());
        }
    }

I change the readline with read and it work, so the assumption that "\n" is the problem is correct.

The thread : a minor change in the thread (remove the reading request part since I already done that in the server)

The Client: change the readline into read just like the server one.

Thank you all for the help

Answer 2

According to the javaDoc, the server response actually is

"My Message:\n"+System.getProperty("line.separator")

I bet, in.readLine() works fine at least once - but you just ignore the response, because the print command is outside the loop. Move that one up, and you should see the responses on the console.

There is a (very small) chance, that the servers println() doesn't really send a \n char. So you could try this at the thread code:

 out.print(clientResponse+"\n\n");  // exchanged println with an extra \n char

Answer 3

Okay, I've figured this one out. It's not the client that hangs, it's the server. It tries to read a line of text from the client, but the client doesn't send the line separator:

    out.write("My message");
    out.flush();

Replace write() with println() here.

Answer 4

out.write("My message");

That doesn't send a line terminator so it can never be read. Use println().

out.println(clientResponse+"\n");

That will send the clientResponse plus a newline plus a \n. The last part will probably be interpreted as a blank line. Not much point in that. Remove the \n.

do{
    response = in.readLine(); //This is where the code hang
}while (response.length()<= 0);

That's not the correct way to read lines. It will get an NPE at EOS; the response length can never be negative; and why would you send yourself blank lines? The correct way is this:

while ((response = in.readLine()) != null) {
    // if (response.length() == 0) continue; // if you must
    // process the line
}
// when you get here EOS has occurred.

Answer 5

Could it be because clientResponse (sent by server thread) is null and the client is waiting for response size > 0?