Java Echo Server

Question

Hello guys I am trying to do an echo Server by java but it is nnot working .. .I don't know why .. but it seems like the server is waiting the client and the client is waiting the server ... so they can't deliver the infromation to each other ..

here is the code for the Server

    ServerSocket server = null;
        try {
             server = new ServerSocket(3333);
              System.out.println("Listening on 3333");
    } catch (IOException ex) {
        System.out.println("Error can't connect to 3333");
        System.exit(1);
    }

        Socket clientSocket = null;
    try {
        clientSocket = server.accept();
    } catch (IOException ex) {
        System.out.println("Accept fail");
        System.exit(1);
    }
    PrintWriter out = null;
    try {
         out = new PrintWriter(clientSocket.getOutputStream());
    } catch (IOException ex) {
        Logger.getLogger(JavaApplication20.class.getName()).log(Level.SEVERE, null, ex);
    }
    BufferedReader br = null;
    try {
        br = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
    } catch (IOException ex) {
        Logger.getLogger(JavaApplication20.class.getName()).log(Level.SEVERE, null, ex);
    }
    BufferedReader stdIn = new BufferedReader(new InputStreamReader(System.in));

    String inputLine, outputLine;
 while(!(inputLine=br.readLine()).equals("bye"))
            {
                out.print("echo: " + inputLine);

            }
    out.close();
    br.close();
    clientSocket.close();
    server.close();
    System.out.println("Server Exited");

and here is the code for the client

 Socket client = null;
   try {
        client = new Socket("localhost", 3333);
        System.out.println("Connected on 3333");
    } catch (UnknownHostException ex) {
        System.out.println("Couldn't connect to the server");
        System.exit(1);
    } catch (IOException ex) {
        Logger.getLogger(KnockKnockClient.class.getName()).log(Level.SEVERE, null, ex);
    }


    PrintWriter out = null;
    BufferedReader in = null;
    BufferedReader stdIn = null;

    try {
        out = new PrintWriter(client.getOutputStream(), true);
    } catch (IOException ex) {
        Logger.getLogger(KnockKnockClient.class.getName()).log(Level.SEVERE, null, ex);
    }
    try {
        in = new BufferedReader(new InputStreamReader(client.getInputStream()));
    } catch (IOException ex) {
        Logger.getLogger(KnockKnockClient.class.getName()).log(Level.SEVERE, null, ex);
    }
    stdIn = new BufferedReader(new InputStreamReader(System.in));

    String fromServer, fromUser;


    while((fromUser=stdIn.readLine())!=null)
        {
            System.out.println("From user: "+ fromUser);

            out.print(fromUser);
            fromServer=in.readLine();
            System.out.println(fromServer);
        }



    out.close();
    stdIn.close();
    in.close();
    client.close();

    System.out.println("client Exited");

Any Help with that ??

Answer 1

After out.print(fromUser); use out.flush() in your client and server. flush will make sure it will right to the socket.

while((fromUser=stdIn.readLine())!=null)
    {
        System.out.println("From user: "+ fromUser);

        out.print(fromUser);
        out.flush();
        fromServer=in.readLine();
        System.out.println(fromServer);
    }



out.close();
stdIn.close();
in.close();
client.close();

Regarding flush, Extracted from java doc.

Flushes the stream. If the stream has saved any characters from the various write()      methods in a buffer, write them immediately to their intended destination. Then, if that destination is another character or byte stream, flush it. Thus one flush() invocation will flush all the buffers in a chain of Writers and OutputStreams. 

  If the intended destination of this stream is an abstraction provided by the underlying operating system, for example a file, then flushing the stream guarantees only that bytes previously written to the stream are passed to the operating system for writing; it does not guarantee that they are actually written to a physical device such as a disk drive.

Answer 2

You're sending some string from the client ("Hello" for example), and you're trying to read it with readLine() on the server (and vice versa). readLine() will only return once it finds an EOL character, or once the input stream is closed.

Since the client doesn't send any EOL char, the server waits indefinitely, and the client also because it waits for the answer from the server.

Send "Hello\n", and it will work better.