Unable to read output from server on a socket

Question

Hello everyone,
I am trying to re-develop and application that traditionally is developed in VB.
Traditional program does following: communicates with host using telnet; login, send some text, read the output from server, validates output and terminated telnet connection.
I am trying to build same kind of application in Java using sockets, but I do not get any response from the server.
Any Suggestions ?
Thanks,
Code below:
String hostName="ip address here";
int portNum=23; //Verified that server's telnet runs on port 23
try
socket=new Socket(hostName,portNum);
out=new PrintWriter(socket.getOutputStream(),true);
in=new BufferedReader(new InputStreamReader(socket.getInputStream()));
}catch(UnknownHostException e){
System.err.println ("Host not found: " + hostName);
System.exit(1);
}catch(IOException e){
System.err.println("Could not get I/O for host: " + hostName + "on port: " + portNum);
System.exit(1);
BufferedReader stdin=new BufferedReader(new InputStreamReader(System.in));
String userInput;
try{
while ((userInput=stdin.readLine()) != null)
out.println(userInput);
while (in.readLine() != null){
System.out.println("echo: "+in.readLine()); // I Expect server's output here but nothing happens.
}catch(IOException e){
System.err.println("User Input not read.");

Answer 1

while (in.readLine() != null){
System.out.println("echo: "+in.readLine()); // I Expect server's output here but nothing happens.I see two problems here:
1) in.readLine() only returns null if the socket is closed. You will be forever in that loop.
2) you are losing every second line of your input. If your telnet server sends only one line at the beginning, the readline() call in the while statement will swollow that.
If you want to do this in a single thread, you will have to use a method which won't block until input is available, such as the read(char[], int, int) method of BufferedReader.
You could also use two threads, of which one is printing the output and the other is taking user input. This has the advantage, that you are able to handle any connection errors immediatley instead of only when the user entered a command.
Does telnet send information about the end of an input sequence (like the end of the welcome message and the end of the answer to any issued command? If not, I'd say that you should use two threads, as you would have to do polling all the time otherwise.
Hope it helps.