Server Socket does not read data input stream

Question

Hi all,
I am very newbie to Java Network programming with sockets and multi-threading.
But I am obliged to develop a chat system written in Applets which can be placed on the website and used by visitors who come to my website.
In order to understand this, I have tested a basic web chat program I downloaded from the Internet which use sockets and multi-threadings. The program work fine, no bugs at all at both compilation and run time. I noticed that all three streams for Client side (i.e. first one is input stream used receiving data from User; the second one is socket input stream used for receiving data from Server socket, and the third is socket output stream used for writing data to server socket) were established. And the same, two socket streams (input & output) for Server side were also connected when running program giving right port number and IP address of the server.
The problem is both server and client sockets do not read data using the following stream classes:
1. DataStreamInput: I use input.readUTF() method
2. or BufferedReader: I use input.readLine() method
The example of the codes are below:
private BufferedReader input = null;
private PrintWriter output = null;
private Socket socket = null;
public void open() throws IOException
{  input = new BufferedReader(new
InputStreamReader(socket.getInputStream()));
System.out.println("Server socket input stream was created, and");
output = new PrintWriter(socket.getOutputStream());
System.out.println("Server socket output stream was created");
public void run()
{  System.out.println("Server Thread " + clientPort + " running.");
while (true)
{  try
System.out.println("Server is reading data from Client, wait...");
String fromClient = input.readLine();
System.out.println("Server received a message on " + clientPort + ".");
catch(IOException ioe)
{  System.out.println(clientPort + " ERROR reading: " + ioe.getMessage());
server.remove(clientPort);
stop();
The problem is at the line: String fromClient = input.readLine(); in the run() method? What is wrong with the codes above?
Note: I also try to use original codes which use readUTF() method in DataStreamInput class instead using readLine() in BufferedReader. Both methods dont read data from inputstream socket?
I very appreciate any help/advice from experienced developers.
Best regards

Answer 1

Hi,
Yes. The readLine() method hangs! After the test, the execuation of the program is stopped at the line of readLine() method; it does not pass it?
There is no problem with writing to Server socket. After the test, the program pass through flush() method. Here is the code for writing to sever socket within ChatClient (client side socket) class:
private BufferedReader input = null;
private PrintWriter           output = null;
public ChatClient(String serverName, int serverPort)
{  System.out.println("Establishing connection. Please wait ...");
try
{  socket = new Socket(serverName, serverPort);
System.out.println("Connected: " + socket);
start();
catch(UnknownHostException uhe)
{  System.out.println("Host unknown: " + uhe.getMessage()); }
catch(IOException ioe)
{  System.out.println("Unexpected exception: " + ioe.getMessage()); }
public void start() throws IOException
{  input   = new BufferedReader (new
                         InputStreamReader(System.in));
System.out.println("Client User input stream was created,");
output = new PrintWriter(socket.getOutputStream());
System.out.println("Client Socket output stream was established, and");
if (thread == null)
{  client = new ChatClientThread(this, socket);
thread = new Thread(this);
thread.start();
public void run()
     while (thread != null) {
     String fromUser;
          try{
               while((fromUser = input.readLine())!= null)
               System.out.println("Client wasreading a data from User, and");
output.println(fromUser);
     output.flush();
     System.out.println("Client has written a data to Server");
catch(IOException ioe)
{  System.out.println("Sending to server error: " + ioe.getMessage());
stop();
etc.
Here is a piece of codes for reading data from the Client Socket in the ChatServer Class (Server Side socket):
public void run()
{  System.out.println("Server Thread " + clientPort + " running.");
while (true)
{  try
{  //server.handle(clientPort, input.readLine());
System.out.println("Server is reading data from Client, wait...");
String fromUser = input.readLine();
//while((fromUser = input.readLine()) != null)
     System.out.println("Server received a message on " + clientPort + ".");
catch(IOException ioe)
{  System.out.println(clientPort + " ERROR reading: " + ioe.getMessage());
server.remove(clientPort);
stop();
etc. Please advice why the readLine() method hangs; does not read data from the input stream received from the CLIENT?