1. Li Tak Sing COMPS311F

2. Case study: a multithreaded chat server The source contains 3 files: ChatServer //the chat server ChatThread //the thread on the server side to handle a client ChatClient //the client The source can be obtained at: http://plbpc001.ouhk.edu.hk/~mt311f/2010-sep/chat.zip

3. ChatServer The ChatServer class is the main program for the chat server. It will create a ServerSocket at port 12345. For each of the incoming requests, a ChatThread will be created to entertain the request. It is a subclass of JFrame. The window is used to display information regarding the connected clients and messages passed.

4. ChatServer The upper textfields will show the connected clients. The central textarea will show the messages from the clients.

5. Attributes of ChatServer Vector threads; //connected clients JTextField clientText; //for displaying the connected clients JTextArea text; //for displaying the messages from the clients

6. Methods of ChatServer synchronized public void addThread(ChatThread th); //this method adds the ChatThread to threads. synchronized public void removeThread(ChatThread th) ; //this method removes the ChatThread from threads. synchronized public void broadcast(String st); //this method is used to send a message to all connected clients.

7. ChatThread It is created to entertain an individual request. It is a subclass of Thread. When a ChatThread is created, it will be added to threads of ChatServer by using the addThread method of ChatServer. The run method of ChatThread will continuously read from the corresponding client. When a message is read from the client, it will be broadcast to all connected clients through the broadcast method of ChatServer. It also provide a sendMessage method for sending a message to the corresponding client.

8. Attributes of ChatThread String name; //name of the client Socket socket; //socket of the connection between the server and the client. ChatServer server; //the ChatServre DataInputStream input; //the input stream for the connection with the client. DataOutputStream output; //the output stream

9. Constructor of ChatThread public ChatThread(java.net.Socket s, ChatServer server) This construct allows ChatThread to record the socket and the server. The socket is used to create the data streams. The server is used to broadcast a message.

10. Methods of ChatThread public synchronized void sendMessage(String st) throws IOException ; //this method is used to send a message to the client public void run(); //this will continuously read from the client. After reading a message, it will invoke the server's broadcast method to send the message to all connected clients.

11. ChatClient It is the chat client. It is a subclass of JFrame. The top panel contains a textfield for the user to type in a name. This will be the id of the client in the chat system. The central textarea is used to display all messages from clients. The bottom panel contains a textfield for the user to type in a message.

12. Attributes of ChatClient JTextField name; //This allows the user to type in name JTextArea messages; //This is used to display messages from all connected clients. JTextField text; //This allows the user to type in message to be sent to all clients. DataInputStream input; //This is the input stream for the connection. DataOutputStream output; //The output stream.

13. Constructor of ChatClient public ChatClient() ; //the constructor does all things. It setups the window. All listeners are created using anonymous classes. A thread is created to continuously read from the server. When a message is read, it will be appended to the central textarea, messages.

14. Implementation of constructor of ChatServer... try { java.net.ServerSocket ss = new java.net.ServerSocket(12345); while (true) { java.net.Socket s = ss.accept(); ChatThread thread = new ChatThread(s, this); } } catch (Exception e) { e.printStackTrace(); }...

15. Implementation of methods of ChatServer synchronized public void addThread(ChatThread th) { threads.add(th); String st = ""; for (ChatThread thread:threads) { st+=thread.name()+" "; } clientText.setText(st); }

16. Implementation of methods of ChatServer synchronized public void removeThread(ChatThread th) { threads.remove(th); String st=""; for (ChatThread thread:threads) { st+=thread.name()+" "; } clientText.setText(st); }

17. Implementation of methods of ChatServer synchronized public void broadcast(String st) { text.append(st); java.util.Vector removedThreads = new java.util.Vector (); for (ChatThread th : threads) { try { th.sendMessage(st); } catch (Exception e) { removedThreads.add(th); } for (ChatThread th : removedThreads) { removeThread(th); }

18. Implementation of constructor of ChatThread public ChatThread(java.net.Socket s, ChatServer server) { socket=s; this.server=server; try { output=new java.io.DataOutputStream(socket.getOutputStream()); input=new java.io.DataInputStream(socket.getInputStream()); name=input.readUTF(); server.addThread(this); start(); } catch (Exception e) { e.printStackTrace(); }

19. Implementation of methods of ChatThread public synchronized void sendMessage(String st) throws IOException { output.writeUTF(st); }

20. Implementation of methods of ChatThread public void run() { try { while (true) { String st=input.readUTF(); server.broadcast(name+":"+st); } catch (Exception e) { server.removeThread(this); }

21. The ActionLister of the connect button public void actionPerformed(ActionEvent e) { if (button.getText().equals("connect")) { try { s = new java.net.Socket("127.0.0.1", 12345); input = new java.io.DataInputStream(s.getInputStream()); output = new java.io.DataOutputStream(s.getOutputStream()); output.writeUTF(name.getText()); messages.append("connected\n"); button.setText("disconnect");

22. The ActionLister of the connect button new Thread() { public void run() { try { while (true) { String st = input.readUTF(); messages.append(st); } } catch (Exception e) { messages.append("Disconnected\n"); button.setText("connect"); } }.start();

23. The ActionLister of the connect button } catch (Exception ee) { button.setText("connect"); messages.append("disconnected"); } } else { try { input.close(); output.close(); s.close(); button.setText("connect"); messages.append("disconnected"); } catch (Exception ee) { } });