BufferedReader.readLine doesn't return null

Question

Hi there,
I'm trying to put together a simple Chat client/server application. The issue I'm having is with the Server app. I have a class that extends Thread which contains this call:
temp = input.readLine()
in the run() method. Everytime I connect with the client side app, an instance of this class "ReceivingThread" is created and is supposed to read in any messages coming in using a BufferedReader. That's the input variable type. According to the API readLine() is supposed to return null when there's nothing more to read in. In my code I check for null but it never seems to leave the while loop.
Please advise,
Alan
package vcserver;
import java.io.*;
import java.net.*;
import java.util.StringTokenizer;
public class ReceivingThread extends Thread
  private BufferedReader input;
  private MessageListener messageListener;
  private boolean keepListening = true;
  public ReceivingThread(MessageListener listener, Socket clientSocket)
       super("ReceivingThread: " + clientSocket);
       messageListener = listener;
       try
            clientSocket.setSoTimeout(5000);
            input = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
       catch(IOException ioe){ioe.printStackTrace();}
  public void run()
       StringBuffer messageBuffer = new StringBuffer();
       String temp = "";
       try
          START:
          while(keepListening)
             while(true)
                try
                              temp = input.readLine();
                catch(InterruptedIOException iioe)
                              continue;
                catch(IOException ioe){break;}
                   if(temp != null)
                try
                   System.out.println("temp: " + temp);
                   messageBuffer.append(temp);               
                 catch(Exception e)
                   e.printStackTrace();
                   break START;
                else
                break;
             System.out.println("out of while loop...message:\n" + messageBuffer.toString());
             String message = messageBuffer.toString();
             StringTokenizer tokenizer = new StringTokenizer(message, Constants.MESSAGE_SEPERATOR);
              if(tokenizer.countTokens() == 2)
          System.out.println("message received");
          messageListener.messageReceived(tokenizer.nextToken(), tokenizer.nextToken());
              else
          if(message.equalsIgnoreCase(Constants.MESSAGE_SEPERATOR + Constants.DISCONNECT_STRING))
          stopListening();
         input.close();
       catch(IOException ioe){ioe.printStackTrace();}
  public void stopListening()
       keepListening = false;
}Edited by: ashiers on Nov 20, 2007 10:51 AM

Answer 1

Not to mention garbage ...
readLine() returns null when there is nothing more to read, i.e. when the other end has closed its socket. If the other end hasn't closed its socket it won't return null, it will block. There might be more data coming later, at which time readLine() will unblock and read it and return it.