How to pass a string from a child thread to a parent thread ?

Question

I have a Server class listening to a particular port continuously using TCP Sockets . Whenever a client connects to this server socket, a new thread is created to obtain the data from the client socket. The following code shows how this is done -
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.*;
public class TransportHandler extends Thread{
          ServerSocket server_socket;
          int myListeningPort;
          public String clientReq = "";
          public TransportHandler() throws IOException{
               super();
               myListeningPort = 80;
               CreateServSocket();
          //throw the socket exception outside, so that it can be handled
          public TransportHandler(int port) throws IOException{
               super();
               myListeningPort = port;          
               CreateServSocket();
          private void CreateServSocket() throws IOException{
                        //create serversocket
               server_socket = new ServerSocket(myListeningPort);
          public void printmsg(){
               System.out.println(clientReq);
          @Override
          public void run() {
               // TODO Auto-generated method stub
               StartListening();
          public void StartListening(){
               while(true){
                    //loop forever listening to connections
                    try {
                         Socket clientSocket = server_socket.accept();
                                         //create new thread to handle client connection
                         Thread clientthread = new Thread(new ClientConnectionHandler(clientSocket));
                         clientthread.setName("Client Handler");
                         clientthread.start();
                         printmsg();
                    } catch (IOException e) {
                         // TODO Auto-generated catch block
                         e.printStackTrace();
          public void StoreReq(String msg){
               clientReq.concat(msg);
          private class ClientConnectionHandler implements Runnable{
               Socket ClientSock;
               BufferedReader sockReader;
               InputStreamReader isReader;
               String messageFromClient;
               public ClientConnectionHandler(Socket sock){
                    ClientSock = sock;
                    try {
                         isReader = new InputStreamReader(ClientSock.getInputStream());
                         sockReader = new BufferedReader(isReader);
                    } catch (IOException e) {
                         // TODO Auto-generated catch block
                         e.printStackTrace();
               @Override
               public void run() {
                    // TODO Auto-generated method stub
                    int c= 0;
                    try {
                         while( (messageFromClient = sockReader.readLine())!= null){
                              StoreReq(messageFromClient);  
                         //System.out.println("clientreq = "+clientReq);
                    } catch (IOException e) {
                         // TODO Auto-generated catch block
                         e.printStackTrace();
}The TransportHandler is instantiated from another class HttpMessageHandler as shown below -
import java.io.IOException;
public class HttpMessageHandler {
     public static void main(String[] args){
          try {
               TransportHandler server = new TransportHandler();
               server.start();
          } catch (IOException e) {
               // TODO Auto-generated catch block
               e.printStackTrace();
}So in the above code when the server.start() is executed, the run() method in TransportHandler is executed. How do I get the string contained in clientReq in HttpMessageHandler after the data from client socket is fully read ?
Edited by: turing09 on Dec 12, 2009 2:13 PM

Answer 1

Okay, to make my problem more clear to you - basically I am trying to create a simple Http Server, wherein the HttpMessageHandler is an interface between the Http layer & the Transport layer (represented by TransportHandler class). I am trying to code it bottom-up. In my design I require the TransportHandler class to get the client http request data from the TCP socket and pass it onto the HttpMessageHandler class.
At the same time TransportHandler class must continuously listen to the port to receive other connections. For every client connection, the TransportHandler creates a new ClientHandler thread & this new thread gets the data. The TransportHandler instance & the ClientHandler instance are running in seperate threads. The HttpMessageHandler is running in the main thread. Please note: the member variable clientReq is private & not public
The problem I am facing here is that even when the ClientHandler thread finishes, I am not able to print the client request data in HttpMessageHandler thread.
I am able to print the String in the run() method of ClientHandler but not in HttpMessageHandler main() method.
Any solutions for this?
Edited by: turing09 on Dec 12, 2009 5:24 PM
Edited by: turing09 on Dec 12, 2009 5:25 PM