how to check active connections in both client and server applications

Try this:


import java.io.*;
import java.net.*;

public class ServerPing {
  public static void main ( String [] args ) {
   
    int port = 22;  // Change me to the port to connect to the server on..
    String server = "serverName";
    Socket sock = null;
   
    for ( ;; ) {
        boolean bTemp = false;
        try {
            System.out.println( "\nConnecting ..." );
            InetAddress addr = InetAddress.getByName( server );
           
            sock = new Socket ( addr, port );
           
            System.out.print ( "\nConnection Made ... " );
        } catch (Exception e) { System.out.println( "Exception occurred" ); bTemp = true; }
            if ( !bTemp ) {
                System.out.println( "Connection lost" );
            }
            while ( sock.isConnected() ) {}
    }
  }
}

gL,
[r.D]

There must be something else wrong here, the method mySocket.isClosed( ) will return true if you kill the server and you should be able to use that.

Maybe you should make a small example that shows where the isClosed() method returns false, when it should return true. Post the code here, and we will see where is the bug.

I added a print out in the while loop
  while ( sock.isConnected() ) {}
 
to
  while ( sock.isConnected() )
{
 System.out.println("still connected: " + sock.isConnected() );
}

ran the server, ran the client, connection was made, killed the server
the client endlessly printed
still connected: true

I'll post the server code as soon as I can
I'm running the programs on linux, not that I think that should matter

I think the only thing I've modified in this program I found is adding print outs and the port number to 6006, there are two files

mport java.net.*;
import java.io.*;

public class KnockKnockServer {
    public static void main(String[] args) throws IOException {

        ServerSocket serverSocket = null;
        try {
            serverSocket = new ServerSocket(6006);
        } catch (IOException e) {
            System.err.println("Could not listen on port: 6006.");
            System.exit(1);
        }

        Socket clientSocket = null;
        try {
            clientSocket = serverSocket.accept();
        } catch (IOException e) {
            System.err.println("Accept failed.");
            System.exit(1);
        }

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(
                        new InputStreamReader(
                        clientSocket.getInputStream()));
        String inputLine, outputLine;
        KnockKnockProtocol kkp = new KnockKnockProtocol();

        outputLine = kkp.processInput(null);
        out.println(outputLine);

        while ((inputLine = in.readLine()) != null) {
                  System.out.println("isBound() = " + serverSocket.isBound());
                  System.out.println("isClosed() = " + serverSocket.isClosed());
                  System.out.println("kkSocket.getSoTimeout() = " + serverSocket.getSoTimeout());
             outputLine = kkp.processInput(inputLine);
             out.println(outputLine);
             if (outputLine.equals("Bye."))
                break;
        }



        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();

                  System.out.println("isBound() = " + serverSocket.isBound());
                  System.out.println("isClosed() = " + serverSocket.isClosed());
                  System.out.println("kkSocket.getSoTimeout() = " + serverSocket.getSoTimeout());
    }
}
////////////////////////////////////////
import java.net.*;
import java.io.*;

public class KnockKnockProtocol {
    private static final int WAITING = 0;
    private static final int SENTKNOCKKNOCK = 1;
    private static final int SENTCLUE = 2;
    private static final int ANOTHER = 3;

    private static final int NUMJOKES = 5;

    private int state = WAITING;
    private int currentJoke = 0;

    private String[] clues = { "Turnip", "Little Old Lady", "Atch", "Who", "Who" };
    private String[] answers = { "Turnip the heat, it's cold in here!",
                                 "I didn't know you could yodel!",
                                 "Bless you!",
                                 "Is there an owl in here?",
                                 "Is there an echo in here?" };

    public String processInput(String theInput) {
        String theOutput = null;
      System.out.println("knock knock 6006");
        if (state == WAITING) {
            theOutput = "Knock! Knock!";
            state = SENTKNOCKKNOCK;
        } else if (state == SENTKNOCKKNOCK) {
            if (theInput.equalsIgnoreCase("Who's there?")) {
                theOutput = clues[currentJoke];
                state = SENTCLUE;
            } else {
                theOutput = "You're supposed to say \"Who's there?\"! " +
                      "Try again. Knock! Knock!";
            }
        } else if (state == SENTCLUE) {
            if (theInput.equalsIgnoreCase(clues[currentJoke] + " who?")) {
                theOutput = answers[currentJoke] + " Want another? (y/n)";
                state = ANOTHER;
            } else {
                theOutput = "You're supposed to say \"" +
                      clues[currentJoke] +
                      " who?\"" +
                      "! Try again. Knock! Knock!";
                state = SENTKNOCKKNOCK;
            }
        } else if (state == ANOTHER) {
            if (theInput.equalsIgnoreCase("y")) {
                theOutput = "Knock! Knock!";
                if (currentJoke == (NUMJOKES - 1))
                    currentJoke = 0;
                else
                    currentJoke++;
                state = SENTKNOCKKNOCK;
            } else {
                theOutput = "Bye.";
                state = WAITING;
            }
        }
        return theOutput;
    }
}

OK. Do give both client and the server, minimized as much as possible, so we can see the problem faster.

Please post the client also. Difficult to trace without that.

I tried your server with my own simple client, and it still works as I expected: the server reads the first line and then exits. The client call to mySocket.isClosed() returns true.

So I really need your client.

I think I got it. Short answer first: You can use java.net.SocketException to do what you need. Just catch the java.net.SocketException and go to reconnect phase.

This is the part on the client, where you send the data:

        OutputStreamWriter osw = new OutputStreamWriter(mySocket.getOutputStream());
        osw.write("Whatever you want to send\n");
        try
        {
          osw.flush();
        }
        catch (java.net.SocketException e)
        {
          System.out.println("Server closed. You should reconnect here");
        }

The reason why I was getting isClosed = true is because I was closing the stream with osw.close().

dejanpazin,
I was using the client given by DrWarezz's post.

I will try your recomendation first thing in the morning,
thanks

still not working for me, I've reduced my test code, here is the client and server I am trying.
when the server is stopped the client dies along with it, without generating an exception
///////////////////////CLIENT
import java.io.*;
import java.net.*;

public class ServerPing
{

   Socket createSocket(String IP, int port)
    {
      Socket newSocket = null;

      try
          {
            System.out.println("attemping to connect to server");
            newSocket = new Socket(IP, port);
          }
      catch (UnknownHostException e)
          {
            System.err.println("Don't know about host: localhost.");
          }
      catch (IOException e)
          {
            System.err.println("Couldn't get I/O for the connection to: localhost.");
          }
      return newSocket;
    }

    public static void main( String[] args)
    {
      int port = 6006;
      String server = "localhost";
      Socket mySocket = null;
      ServerPing sp = new ServerPing();
        PrintWriter out = null;
        BufferedReader in = null;
        String fromServer;
      try
          {
            while(mySocket == null)
                {
                  System.out.println("attemping to connect to server");
                  mySocket = sp.createSocket("localhost", 6006);
                }

            System.out.println("\nConnection made..");

            out = new PrintWriter(mySocket.getOutputStream(), true);
            in = new BufferedReader(new InputStreamReader(mySocket.getInputStream()));

            while ((fromServer = in.readLine()) != null)
                {
                  System.out.println("Server: " + fromServer + "\n");
                  out.println("Hello from client");
                  try
                      {
                        Thread.sleep(200);
                      }
                  catch(InterruptedException e)
                      {
                        System.out.println(e);
                      }
                }
            for(int i=0; i<10;i++)
                {
                  out.flush();
                  out.println("Hello from client");
                  System.out.println("should generate exception?");
                }
          }
      catch(java.net.SocketException e)
          {
            System.out.println("need to re-connect to server");
                              while(mySocket == null)
                {
                  System.out.println("attemping to re-connect to server");
                  mySocket = sp.createSocket("localhost", 6006);
                }

          }
      catch (UnknownHostException e)
          {
            System.err.println("Don't know about host: localhost.");
          }
      catch (NullPointerException e)
          {
            System.out.println("NULL POINTER exception");
          }
      catch (IOException e)
          {
            System.err.println("Couldn't get I/O for the connection to: localhost.");
            while(mySocket == null)
                {
                  System.out.println("attemping to re-connect to server");
                  mySocket = sp.createSocket("localhost", 6006);
                }
          }
    }
}


//////////////////SERVER

import java.net.*;
import java.io.*;

public class ServerTest
{
    public static void main(String[] args) throws IOException
    {

        ServerSocket serverSocket = null;
        try
          {
            serverSocket = new ServerSocket(6006);
          }
      catch (IOException e)
          {
            System.err.println("Could not listen on port: 6006.");
            System.exit(1);
          }

        Socket clientSocket = null;
        try
          {
            clientSocket = serverSocket.accept();
            if(clientSocket != null)
                {
                  System.out.println("CONNECTION ACCEPTED");
                }
          }
      catch(java.net.SocketException e)
          {
            System.out.println("SERVER ERROR1:" + e);
          }
      catch (IOException e)
          {
            System.err.println("Accept failed.");
          }

        PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
        BufferedReader in = new BufferedReader(
                                     new InputStreamReader(
                                                     clientSocket.getInputStream()));
        String inputLine, outputLine;
   
      out.println("Hello from Server");
      try
          {
            while ((inputLine = in.readLine()) != null)
                {
                  System.out.println("from client: " + inputLine + "\n");
                  out.println("Hello from Server");
                }
          }
      catch(java.net.SocketException e)
          {
            System.out.println("SERVER ERROR2: " + e);
          }

        out.close();
        in.close();
        clientSocket.close();
        serverSocket.close();
    }
}