Java Sockets - EOFException when trying to implement multi-threading

Question

I think it's because when I multi-thread the client&server, the DataOutputStream and DataInputStream buffers I use get overwritten or something like that since the socket can only have 1 duplex connection.

Here's what I have for now:

Client Class in my client program:

public static void main(String args[]) throws UnknownHostException, IOException, InterruptedException {
        for (int i=0;i<2;i++) //change limit on i to change number of threads
        {
            new Thread(new ClientHandler(i)).start();
        }
        Thread.sleep(10000);

ClientHandler class in my client program: (Sends a value to the server, the server will echo it back).

public class ClientHandler implements Runnable {
public int clientNumber;
public ClientHandler(int i){
    this.clientNumber=i;
}
public void run() {
        Socket socket = null;
        try {
            socket = new Socket("localhost",9990);
            System.out.println("connected client number "+clientNumber);
            DataOutputStream output = new DataOutputStream(socket.getOutputStream());
            DataInputStream input = new   DataInputStream(socket.getInputStream());
            output.writeDouble((new Random()).nextDouble());
            System.out.println(input.readDouble());
            } catch (UnknownHostException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }finally{
                try {
                    socket.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }

Server Class in my server program:

    ServerSocket socket = new ServerSocket(9990);
    try { 
        while (true) {
            Socket threadSocket = socket.accept();
            new Thread(new ServerHandler(threadSocket)).start();
            Thread.sleep(10000);
}
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    finally {
        socket.close();
        }
    }
}

ServerHandler Class in my server program (receives value from client and echoes it back)

public class ServerHandler implements Runnable {
    private Socket socket;
    public ServerHandler(Socket socket) {
    this.socket = socket;
}

public void run() {
    while(true) {
      try {
            DataInputStream input = new DataInputStream(socket.getInputStream());
            DataOutputStream output = new DataOutputStream(socket.getOutputStream());
    double a = input.readDouble();
            output.writeDouble(a);

}catch (IOException e){
      e.printStackTrace();

  }
}

}

So it's a pretty straight-forward implementation: create multiple threads of the client, and connect them to multiple threads of the server.

Everything works fine until the line:

double a = input.readDouble();

in my ServerHandler class.

I get an EOFException

I'm guessing it's because there can only be a single duplex connection between sockets. But if that's the case then how would I implement multi-threading of sockets at all?

So my question is: how can I get rid of the EOFException and allow myself to perform multi-threaded client-server socket interaction?

(preferably not changing much about my code because it's taken me a long time to get to this point).

Why do you need Thread.sleep(10000);? Plus, can you post the stack trace? — Burkhard
– Burkhard, Commented Oct 22, 2015 at 9:42
I had seen Thread.sleep(10000) in an example and just used it - not entirely sure what it's doing. How do I post the stack trace? — user83676
– user83676, Commented Oct 22, 2015 at 9:43
e.printStackTrace(); prints it in the console. Just copy-paste it in the question. — Burkhard
– Burkhard, Commented Oct 22, 2015 at 9:44
I actually just removed my while(true) loop in my ServerHandler class and randomly am no longer getting an error... it may actually be working! Will update! — user83676
– user83676, Commented Oct 22, 2015 at 9:46

babanin · Accepted Answer · 2015-10-22 08:58:50Z

1

The problem is that you share same Socket variable in ServerHandler for all threads:

private static Socket socket

Remove static keyword. Your ServerHandler will be something like this:

public static class ServerHandler implements Runnable {
    private Socket socket;

    public ServerHandler(Socket socket) {
        this.socket = socket;
    }

    public void run() {
        try {
            DataInputStream input = new DataInputStream(socket.getInputStream());
            DataOutputStream output = new DataOutputStream(socket.getOutputStream());
            double a = input.readDouble();
            output.writeDouble(a);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

answered Oct 22, 2015 at 8:58

babanin

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7 Comments

user83676 Over a year ago

hi, thank you for answering! I removed the static keyword, but I'm still getting EOFExeption when I try to run the code.

babanin Over a year ago

@user83676 can you update code in question with your fixes?

babanin Over a year ago

@user83676 hm your code of ServerHandler looks very strange, because there is no exception handling in run() method... In my version of ServerHandler I added IOException handling.

user83676 Over a year ago

I actually just forgot to put that in my original question - I'll update it here as well.

user83676 Over a year ago

Aha! Thanks for asking about that because it made me write in the while(true){} loop that was causing everything to not work... Code working perfectly now!

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