Networking (Socket) question.

[Tommy Becker]

I've been playing around with the basic chat client code from Head First Java. I extended the initial example to be able to talk to more than 1 client at a time using threads. For those that aren't familiar with the book, the client connects to the server and the server simply sends it a string containing "advice". Anyway, I set it up to loop so once you connect to the server, it sends you a continous stream of advice, about 1 every second. Multiple clients can connect and that works fine. My question is how do I determine when the client is no longer there? If I kill a client using ^C, the server thread sending the data to that client just keeps on trucking. I've tried using the isConnected() method of the socket class to see if the connection is still good but the behavior is the same. I realize that a proper client would call close() but that's not the point. Surely there has to be a way I can tell that the client bailed from the server side. . .

[Ilja Preuss]

Moving to Sockets and Internet Protocols...

[hatim osman]

Hi there...
I am not sure if I clearly understood your question but here is a remark that may be useful:

when working with sockets, any attemp to read or write to a socket that is disconnected "became unreachable after initially was reachable" will throw SocketException. Therefore you can continue send data to a remote client, however, if the client disconnects then an Exception will be thrown. It's a good practice to handle any clean up code in a finally block :

 try {
PrintWriter out = new PrintWriter(mySocket.getOutputStream(), true);
 
//if the client is disconnected then an exception will be thrown
out.println("Advice");
} catch (IOException ioe) {
      //client has disconnected
} finally {
    //clean up
}
 

Hope this is helpful.
Hatim

[Tommy Becker]

Thanks for the reply. I too thought that it would throw an exception, but it doesn't seem to. Here is the class that is sending the data:

class Conversation implements Runnable {
private Socket sock;
String[] adviceList = {"Take smaller bites", "One word: inappropriate", "Just for today, be honest.  Tell your boss what you *really* think", "You might want to rethink that haircut"};

public Conversation(Socket s){
sock = s;
}

private String getAdvice(){
return adviceList[(int) (Math.random()*adviceList.length)];
}

public void run(){
try {
PrintWriter writer = new PrintWriter(sock.getOutputStream());
while(sock.isConnected()){
writer.println(getAdvice());
writer.flush();
Thread.sleep(1000);
}
}catch(Exception ex) {
ex.printStackTrace();
}
}
}
  

I'm catching any and all exceptions there, no? Anyway, when a client connects, I start a thread that runs this code and it never exits, even after I ^C on the client.