Connects to a server at a specified host and port. It reads text from the console and sends it to the server : Socket « Network Protocol « Java

Connects to a server at a specified host and port. It reads text from the console and sends it to the server

 * Copyright (c) 2004 David Flanagan.  All rights reserved.
 * This code is from the book Java Examples in a Nutshell, 3nd Edition.
 * It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
 * You may study, use, and modify it for any non-commercial purpose,
 * including teaching and use in open-source projects.
 * You may distribute it non-commercially as long as you retain this notice.
 * For a commercial use license, or to purchase the book, 
 * please visit

 * This program connects to a server at a specified host and port. It reads text
 * from the console and sends it to the server. It reads text from the server
 * and sends it to the console.
public class GenericClient {
  public static void main(String[] args) throws IOException {
    try {
      // Check the number of arguments
      if (args.length != 2)
        throw new IllegalArgumentException("Wrong number of args");

      // Parse the host and port specifications
      String host = args[0];
      int port = Integer.parseInt(args[1]);

      // Connect to the specified host and port
      Socket s = new Socket(host, port);

      // Set up streams for reading from and writing to the server.
      // The from_server stream is final for use in the inner class below
      final Reader from_server = new InputStreamReader(s.getInputStream());
      PrintWriter to_server = new PrintWriter(s.getOutputStream());

      // Set up streams for reading from and writing to the console
      // The to_user stream is final for use in the anonymous class below
      BufferedReader from_user = new BufferedReader(new InputStreamReader(;
      // Pass true for auto-flush on println()
      final PrintWriter to_user = new PrintWriter(System.out, true);

      // Tell the user that we've connected
      to_user.println("Connected to " + s.getInetAddress() + ":" + s.getPort());

      // Create a thread that gets output from the server and displays
      // it to the user. We use a separate thread for this so that we
      // can receive asynchronous output
      Thread t = new Thread() {
        public void run() {
          char[] buffer = new char[1024];
          int chars_read;
          try {
            // Read characters from the server until the
            // stream closes, and write them to the console
            while ((chars_read = != -1) {
              to_user.write(buffer, 0, chars_read);
          } catch (IOException e) {

          // When the server closes the connection, the loop above
          // will end. Tell the user what happened, and call
          // System.exit(), causing the main thread to exit along
          // with this one.
          to_user.println("Connection closed by server.");

      // Now start the server-to-user thread

      // In parallel, read the user's input and pass it on to the server.
      String line;
      while ((line = from_user.readLine()) != null) {
        to_server.print(line + "\r\n");

      // If the user types a Ctrl-D (Unix) or Ctrl-Z (Windows) to end
      // their input, we'll get an EOF, and the loop above will exit.
      // When this happens, we stop the server-to-user thread and close
      // the socket.

      to_user.println("Connection closed by client.");
    // If anything goes wrong, print an error message
    catch (Exception e) {
      System.err.println("Usage: java GenericClient <hostname> <port>");


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