Thread: Server/Client Applet- Connection Reset Problem

Hi,

I'm wondering can anyone help with a problem I'm having. Basically I'm making a Chat applet that allows clients to connect to a server and exchange messages. I have the messages being exchanged fine but whenever a client closes the connection I keep getting a

java.net.SocketException: Connection reset Error

The program is meant to keep track of the number of clients connected and update the the command line every time a client joins or leaves the Server.

My code is attached below. Any help would be greatly appreciated!
Thanks!

import java.net.*;
import java.io.*;
import java.util.*;
 
public class ChatServerThread extends Thread {
    private Socket socket = null;
    private String name;
    private String inputLine;
    private ArrayList <ChatServerThread> clientList;
    private PrintWriter out; 
    private BufferedReader in;
 
    //Constructor takes a socket and Arraylist of connected clients
    //as parameters
    public ChatServerThread(Socket socket,ArrayList <ChatServerThread> clientList) {
    	super("ChatServerThread");
    	this.socket = socket;
    	this.clientList = clientList;
    }
 
    //Broadcast the message to all connected clients
    //Not synchronized because I synchronized blocks where it is used
    public void sendToAll(String message){
    	for(ChatServerThread c: clientList){
				c.out.println(message);				
		}
    }
    public void run(){
 
    	try {
    			//Create input/output streams
				out = new PrintWriter(socket.getOutputStream(), true);
				in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
				//Read in client name
				name = in.readLine();
				//let everyone know user has joined
				synchronized(this){
					sendToAll( name + " has joined the chatroom ....\n");
 
				}
				//If user wants to leave break and close thread
				while ((inputLine = in.readLine()) != null) {
					//broadcast message to all
					synchronized(this){
						sendToAll(name+" says: "+ inputLine);
					}
				}
				sendToAll( name + " has left the chatroom ....\n");
				//Tidy up
				synchronized(this){
					clientList.remove(currentThread());
				}
				System.out.println("Clients :" +clientList.size() + "\n");
				out.close();
				in.close();
				socket.close();
 
 
        } catch (IOException e) {
       		 e.printStackTrace();
    	}
	}
}
 
//-------------------------------------------------------------------------------------//

import java.net.*;
import java.io.*;
import java.util.*;
 
 
public class ChatServer {
    public static void main(String[] args) throws IOException {
        ServerSocket serverSocket = null;
        Socket clientSocket = null;
 
        //Arraylist to hold all connected clients
        ArrayList <ChatServerThread> clientList = new ArrayList<>();
        final int PORT = 7777;
        boolean listening = true;
 
        try {
        	//Set up server socket
            serverSocket = new ServerSocket(PORT);
            System.out.println("Server now listening on port: " + PORT);
        } catch (IOException e) {
            System.err.println("Could not listen on port:" + PORT);
            System.exit(-1);
        }
 
		//Loop to listen for and connect new clients, 
        while (listening){
			try{
				clientSocket = serverSocket.accept();
				ChatServerThread client = new ChatServerThread
				(clientSocket,clientList);
				//add client to clientList and start the thread
				clientList.add(client);
				System.out.println("Clients :" + clientList.size() + "\n");
				client.start();
 
			} catch (IOException e) {}
		}
 
        serverSocket.close();
    }
}
 
//-------------------------------------------------------------------------------------//

The connection between the server and the client is being interrupted unexpectedly.
Where is the client code? How does the client tell the server that the client wishes to terminate the connection?
Make sure the client properly notifies the server about the upcoming disconnect before pulling the plug.
Then make sure the server can handle it if (really "if" means "when") the client is disconnected unintentionally. For example when power is unexpectedly disconnected.

Hi jps,
Many thanks for your reply! The applet is an assignment for college and we were given the code for the applet and chatclient. The code is below and unfortunately can't be modified as per the brief of the assignment. So I guess I'm asking is there anyway that the server can receive the close notification from the client and handle the close properly on the server side?

/* Our chat client */
import java.applet.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.net.*;
 
class ChatClient extends Panel implements Runnable
{
    /* Display */
    private TextField textfield = new TextField();
    private TextArea textarea = new TextArea();
    private Font font = new Font(Font.SANS_SERIF, Font.PLAIN, 12);
 
    /* Communication */
    private Socket s;
    private PrintWriter pw;
    private BufferedReader br;
 
    public ChatClient(String host, int port, String nickname) {
 
	/* Set up display */
	setLayout(new BorderLayout());
        textarea.setFont(font);
        textfield.setFont(font);
	add(BorderLayout.SOUTH, textfield);
	add(BorderLayout.CENTER, textarea);
 
	/* Associate sendChat with textfield callback */
	textfield.addActionListener(new ActionListener() {
		public void actionPerformed(ActionEvent e) {
		    sendChat(e.getActionCommand());
		}
	    });
 
	try {
	    s = new Socket(host, port);
	    pw = new PrintWriter(s.getOutputStream(), true);
	    br = new BufferedReader(new InputStreamReader(s.getInputStream()));
 
	    /* Send nickname to chat server */
	    pw.println(nickname);
 
	    /* Become a thread */
	    new Thread(this).start();
	} catch (IOException e) {System.out.println(e);}
    }
 
    /* Called whenever user hits return in the textfield */
    private void sendChat(String message) {
	    pw.println(message);
	    textfield.setText("");
    }
 
    /* Add strings from chat server to the textarea */
    public void run() {
 
	String message;
 
	try {
	    while (true) {
		message = br.readLine();
		textarea.append(message + "\n");
	    }
	} catch (IOException e) {System.out.println(e);}
    }
}
 
public class ChatApplet extends Applet
{
    public void init() {
 
	/* Retrieve parameters */
	int port = Integer.parseInt(getParameter("port"));
	String host = getParameter("host");
	String nickname = getParameter("nickname");
 
	/* Set up display */
	setLayout(new BorderLayout());
	add(BorderLayout.CENTER, new ChatClient(host, port, nickname));
    }
}

Originally Posted by CD8ED

So I guess I'm asking is there anyway that the server can receive the close notification from the client and handle the close properly on the server side?

Yes. This is basically what I was saying in post #2.
The client (when the client decides to close their end) should notify the server that the client wishes to close. The server will have to determine if the signal to close has been sent. This is one thing you need to do.
The second thing you need to do is handle the case(s) where the connection is unexpectedly interrupted. That exception will climb to the top of the stack and play king of the hill on your server if you don't do something about it. You can't rely on always getting that ending message from any client.

Thanks again jps, I appreciate the answers/advice! Will try and tackle this tomorrow....... cramming for an exam at the minute Thanks again!