Can't break out of a while loop

Question

Hi, I am doing a networking course, for which an assignment was to write an echo client and server. I did the assignment in Java and it works just fine. However, there is something I don't understand that is bugging me. I wanted a way to stop the server by either detecting when the client entered "quit" or when the user of the server entered "quit". This was not part of the assignment, but after trying many different things I really want to know (1) what I am doing wrong and (2) what the correct way to do things would be.
I tried to put an "if" clause within the while loop so that if the client entered "quit" the server would detect that, close the socket connections, and break the while loop. But... it seems that I have done this wrong and I am not sure why.
(Note - I am not a Java programer - just a beginner, and the course in question isn't a programming course. I did the program below by following some brief guidelines/tutorial. I don't even have any books on Java to consult right now - just ordered few from Amazon for any future projects.)
The code:
// EchoServer.java     - a simple server program. It listens on a predetermined port for an incoming connection.
//                After a client connects they can input a line of text and
//                the server will echo the exact same line back.
import java.io.*;
import java.net.*;
public class EchoServer {
     protected static int DEFAULT_PORT = 3004;
     public static void main (String args[]) throws Exception {
          int portNumber;          
          try {
               portNumber = Integer.parseInt(args[0]);
          } catch (Exception e) {
               portNumber = DEFAULT_PORT;
          ServerSocket myServer = null;
            try{
               myServer = new ServerSocket(portNumber);      
               System.out.println("Echo Server started. Listening on port " + portNumber);
          } catch (IOException e) {
               System.out.println("Could not listen on port: " + portNumber);
               System.out.println(e);
          Socket clientSocket = null;                         
          try{          
                 clientSocket = myServer.accept();
          } catch (IOException e) {
                 System.out.println("Accept failed:  " + portNumber);
               System.out.println(e);
          BufferedReader input = null;     
          PrintWriter output = null;
          try {               
               input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
               output = new PrintWriter(clientSocket.getOutputStream(), true);
          } catch (IOException e) {
               System.out.println(e);
          String theLine;     
          while(true){
               theLine = input.readLine();
               output.println(theLine);     
               output.flush();
                    if (theLine.equals("quit"))  {
                         input.close();
                         output.close();
                         clientSocket.close();
                         myServer.close();     
                         break;
                    }     // end if
          }     // end while     
     }     // end main
}          // end EchoClient

Answer 1

A few observations:
- You might as well exit after you have caught your exceptions, since none of the conditions I see would allow your program to run properly afterwards. You can either do that by a System.exit(int) or a return;
- Although this s an example program, you should take advantage of doing things right. Addining a try-finally would be good for tidying things up. First declare your variables before the main try, otherwise the finally won't be able to do its job. For example (this won't compile as is):
Socket clientSocket = null;
ServerSocket myServer = null;
InputStream in = null;
OutputStream out =null;
try {
  String theLine = null;     
  while( (theLine = input.readLine()) != null ){
    output.println(theLine);     
    output.flush();
    if (theLine.equals("quit"))  {
       break;
  }     // end while
} catch ( IOException ex ) {
  ex.printStackTrace();
} finally {
  if ( in != null ) {
     in.close();
  if ( out != null ) {
     out.close();
  // add other conditions to close other closeable objects
}The reasoning is that if an exception were ever to happen you would be sure that the clean up would be done. In your current example you may risk having an inputstream left open. Also note that BufferedReader.readLine() returns null when its arrived at the end of its content.