It's working, but is it a good or bad design?

Question

hiya
I hope I�m not breaking any forum rules, but any help would be greatly appreciated.
I haven�t really done any programming so far, so finally writing an app with more than few lines of code was something different. Anyways, I managed to write it, but truth be told, I have no idea whether my design choices ( I�m not sure if that�s the right term ) were somewhat good or completely off. Thus, if I don�t know what parts of program are designed badly ( and why they are considered bad), then I won�t know where to improve. So I�m hoping someone could point out ( at least the most obvious )design mistakes I made.
It�s a simple �chat� server where several clients ( up to twenty ) can connect to the server and talk to each other. In essence:
1.server creates new client thread for each newly accepted connection
2.if one of these client threads receives some data from the client, then:
3. this client thread creates new ControlThread object (and passes received data to it )
4. ControlThread object in turn spawns a new thread
5. Finally, this spawned thread will send data to all client apps.
I must point out that I could handle some things better using collection classes. But ignoring that, I�m most interested in other design flaws I made. For example:
a) how scalable is this server app?
b) what would you�ve done differently ( in terms of basic program structure )? Perhaps creating ControlThread object each time data needs to be sent to other client apps is a bad idea
c) etc
package serverchat;
import java.net.*;
import java.io.*;
public class Main {
    public static void main(String[] args) {
        Server.runAll();
class Server{
    static int servPort = 1600;
    static ServerSocket servSock;
    static Thread controlThread;
    static ClientHandling[] clientClass=new ClientHandling[20];
    static int numClients = 0;
    static Socket clientSockets[] = new Socket[20];
    static void runAll(){
        initServer();
        handleClient();
    static void initServer(){
        try{
         servSock = new ServerSocket( servPort );  
         catch(Exception e){}
    static void handleClient(){
        try{
            while(true){
              clientSockets[numClients]  = servSock.accept();
              clientClass[numClients] = new ClientHandling(clientSockets[numClients]);
              numClients ++;               
        catch(Exception e){
/*Each time some clientHandling thread receives data from client,
it creates new ControlThread thread. This thread then sends this data
to all clients connected to this server*/
class ControlThread implements Runnable{
    ClientHandling[] clientClass=new ClientHandling[20];
    int numClients;
    String message;
    Thread t;
    ControlThread(String message){
        this.message = message;
        this.numClients = Server.numClients;
        this.clientClass = Server.clientClass;
        t = new Thread(this);
        t.start();
    public void run(){
        System.out.println("ControlThread has started");
               for(int i= 0; i < numClients; i++){
                   if( clientClass[i] !=null ){
                       tellClients(i);
    /* sends data to all the clients. It does this by calling contrToClient()
     on an object that received this data from the client*/
    void tellClients(int i){
           clientClass.contrToClient(message);
class ClientHandling implements Runnable{
Socket clientSocket;
Thread t;
String message;
OutputStreamWriter clientWrite;
InputStreamReader clientRead ;
BufferedReader readBuf;
BufferedWriter writeBuf;
ClientHandling(Socket s){
clientSocket = s;
startThread();
void startThread(){
t = new Thread(this);
t.start();
public void run(){ 
try{        
clientRead = new InputStreamReader (
clientSocket.getInputStream(), "utf-8");
readBuf = new BufferedReader (clientRead);
catch(Exception e){ 
do{   
try{
clientSocket.setSoTimeout(1000);
message = "";
message = readBuf.readLine();
if ( !message.equals("") ){
informContrThread();
System.out.println(message);
catch(Exception e){
}while ( !message.equals("Stop") );
try{
clientSocket.close();
catch(Exception e){
/*this is the actual method that gets called by ControlThread object and
sends received data to all the client apps*/
void contrToClient( String message){
try{
OutputStreamWriter clientWrite = new OutputStreamWriter (
clientSocket.getOutputStream(), "utf-8");
writeBuf = new BufferedWriter (clientWrite);
catch(Exception e){
try{
writeBuf.write(message + System.getProperty("line.separator"));
writeBuf.flush();
catch(Exception e){   
try{
clientSocket.close(); /* I assume I should close the connection
with client if write() throws an exception? */
catch(Exception e1){}
/*creates new ControlThread object, which in turn will
make sure all client apps receive this data*/
void informContrThread(){
System.out.println("informing contrThread");
new ControlThread(message);
thank you                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           

Answer 1

1.server creates new client thread for each newly accepted connection Good. Make sure the server doesn't do any I/O in the accepting thread, including even construction of input and output streams.
2.if one of these client threads receives some data from the client, then:
3. this client thread creates new ControlThread object (and passes received data to it )Why? What does the Control thread do that the client thread can't do? Does the client thread really create a new Control thread per piece of received data? What's the purpose of the Control thread here?
4. ControlThread object in turn spawns a new thread Again why?
From your description you appear to be creating:
(a) a thread per connection
(b) a thread per piece of received data
(c) another thread per (b)
What you probably need for a chat server is an input thread and an output thread per connection. The output thread should read a queue and the input thread should write to the appropriate queue(s), making sure you don't create a loop by sending the client's own data back to him.
5. Finally, this spawned thread will send data to all client apps.No. Use one output thread per connection, as described above. As writing to a socket can block, you shouldn't use a single thread for writes to more than one client, otherwise the whole system can stall due to one non-co-operating client.
a) how scalable is this server app?It's about as non-scalable as it could possibly be. You will have an explosion of threads per item of data received if you've described it correctly, and you already have too many threads per connection.
b) what would you�ve done differently ( in terms of basic program structure )?Almost everything: see above.
Perhaps creating ControlThread object each time data needs to be sent to other client apps is a bad ideaMost definitely.