Telnet read isuue

Question

Hi all
First of all thanks for taking time to help me with my problem. Let me explain
I have developed a telnet connection program that connects to a switch and interacts with it. But unfortunately when i try to login to the switch after sending the password the switch does not reply.
If i try and connect directly (without the use of my program) with the switch using telnet i can login without any problems.
below is the flow
1. readUntil the prompt "USERNAME>"
2. send the username
3. readUntil the propmt "PASSWORD>"
4. send the password
5. readUntil the prompt "WELCOME>"
i can get to step 5 using the telnet utility. But im not getting the "WELCOME>" prompt when i use my program.
the readUntil() method reads the input and returns what ever that is sent. It reads character by character
While the send(String value) method writes the String value as a byte stream along with a Carriage Return.
When using my program step 5 does not return anything. (The switch doesnt reply) But it provides the correct output when i use a telnet connection.
I have checked Both the read and send methods and cannot find a flaw.
what could be the reasons for this ?
  private StringBuffer readUntil(String pattern) {
    try {
      System.out.println(
      char lastChar = pattern.charAt(pattern.length() - 1);
      StringBuffer sb = new StringBuffer();
      //for timinging out purposes
      long startTime = System.currentTimeMillis();
      long currentTime = 0;
      char ch = ' ';
      while (true) {
        currentTime = System.currentTimeMillis();
        if ( (currentTime - startTime) > TIME_OUT) {
          return sb.append(TIME_OUT_STRING);
        if (ch == lastChar) {
          if (sb.toString().endsWith(pattern)) {
            System.out.println("");
            System.out.println(
            return sb;
        if (in.available() > 0) {
          ch = (char) in.read();
          sb.append(ch);
          System.out.print(ch);
          startTime = System.currentTimeMillis();
        else {
          Thread.sleep(1);
    catch (Exception e) {
      Debug.getInstance().printUsingDebug(e);
      logger.log(Level.SEVERE, "Problem in Reading from stream", e);
    return null;
  private int writeln(String value) {
    try {
      out.write(value.getBytes());
      out.write(13);
    catch (IOException ex) {
      Debug.getInstance().printUsingDebug(ex);
    return ConnectorError.SUCCESS;
}Please note that this program works fine with the same type of switch on several other machines.

Answer 1

currentTime = System.currentTimeMillis();
if ( (currentTime - startTime) > TIME_OUT) Delete that and use Socket.setSoTimeout, and catch SocketTimeoutException below.
if (in.available() > 0) {Delete this test.
else {
Thread.sleep(1);
}Delete this 'else' block. Just let the read() block until data arrives or the timeout occurs.
catch (Exception e) {Here you must distinguish between SocketTimeoutException and IOException. There's not much point in catching anything else.
out.write(value.getBytes());
out.write(13);
  out.write(value+"\r\n".getBytes();
  out.flush();