tcp connection stuck in close_wait java

Question

There are lot of close_wait connection, when ever a client client sends the message to the server and comes out the TCP FSM stuck in the CLOSE_WAIT STATE

This the Client code,

public class Client1 
    {

        private static Socket socket;
        public static void main(String args[])
        {
            try
            {
                String host = "localhost";
                int port = 25000;
                InetAddress address = InetAddress.getByName(host);
                socket = new Socket(address, port);
                //Send the message to the server
                OutputStream os = socket.getOutputStream();
                OutputStreamWriter osw = new OutputStreamWriter(os);
                BufferedWriter bw = new BufferedWriter(osw);
                String number = "2";
                String sendMessage = number + "\n";
                bw.write(sendMessage);
                bw.flush();
                System.out.println("Message sent to the server : "+sendMessage);
                //Get the return message from the server
                InputStream is = socket.getInputStream();
                InputStreamReader isr = new InputStreamReader(is);
                BufferedReader br = new BufferedReader(isr);
                String message = br.readLine();
                System.out.println("Message received from the server : " +message);
            }
            catch (Exception exception) 
            {
                exception.printStackTrace();
            }
            finally
            {
                //Closing the socket
                try
                {   
                    socket.close();   
                }
                catch(Exception e)
                {
                    e.printStackTrace();
                }
            }
        }
    }

This the Server code which listen to the upcoming connection

public class Server1 
{

    private static Socket socket;

    public static void main(String[] args) 
    {
        try
        {

            int port = 25000;
            ServerSocket serverSocket = new ServerSocket(port);
            System.out.println("Server Started and listening to the port 25000");

            //Server is running always. This is done using this while(true) loop
            while(true) 
            {
                //Reading the message from the client
                socket = serverSocket.accept();
                InputStream is = socket.getInputStream();
                InputStreamReader isr = new InputStreamReader(is);
                BufferedReader br = new BufferedReader(isr);
                String number = br.readLine();
                System.out.println("Message received from client is "+number);

                //Multiplying the number by 2 and forming the return message
                String returnMessage;
                try
                {
                    int numberInIntFormat = Integer.parseInt(number);
                    int returnValue = numberInIntFormat*2;
                    returnMessage = String.valueOf(returnValue) + "\n";
                }
                catch(NumberFormatException e)
                {
                    //Input was not a number. Sending proper message back to client.
                    returnMessage = "Please send a proper number\n";
                }

                //Sending the response back to the client.
                OutputStream os = socket.getOutputStream();
                OutputStreamWriter osw = new OutputStreamWriter(os);
                BufferedWriter bw = new BufferedWriter(osw);
                bw.write(returnMessage);
                System.out.println("Message sent to the client is "+returnMessage);
                bw.flush();
            }
        }
        catch (Exception e) 
        {
            e.printStackTrace();
        }
        finally
        {
            try
            {
                socket.close();
            }
            catch(Exception e){}
        }
    }
}

The output TCP FSM

 -bash:~$ netstat -an | grep 25000
    tcp4       0      0  127.0.0.1.25000        127.0.0.1.56459        CLOSE_WAIT 
    tcp46      0      0  *.25000                *.*                    LISTEN   

Answer 1

You're closing the accepted socket in the wrong place. It needs to be inside the accept loop.