使用新端口重新启动Java ServerSocket

Question

I'm trying to write a function to restart my ServerSocket with new port. The new port is provided by the user through the panel (that part of code is correct) in which the restart() function is colled. The new port is saved to the static field portNumString.

The following is my code of the attempt to restart the server. The restarted server is not working. The original port works correctly.

 public static void main(String [] args) throws IOException, ClassNotFoundException
   {         
      runServer(false);
   } 


 public static void runServer(boolean changePort)
   {        
      try
        {
           ServerSocket socket = new ServerSocket(Integer.parseInt(portNumString));
           Server server = new Server(socket);

           while(!changePort)
             {             
               server.accept();  

               if(changePort && socket!=null)
                 {
                   socket.close();                  
                   runServer(false);
                 }                    
             } 
        }
      catch(Exception e)
        {
           System.out.println("EXCEPTION !!! "+e);              
        }        
   }


 public static void restart() throws NumberFormatException, ClassNotFoundException, IOException
   {
      System.out.println("Restart Called... ");
      runServer(true);
   }

EDIT:

The part of code that calls the restart()

         cloesButton.addActionListener(new ActionListener()
                       {
                          @Override
                          public void actionPerformed(ActionEvent e)
                            {                                  
                               portNumString=txtPort.getText();                                   
                               try
                                {
                                  restart();
                                }
                              catch(NumberFormatException e1)
                                {
                                  e1.printStackTrace();
                                }
                            }
                       });

Answer 1

I am assuming restart() is being called from another thread, since the runServer method has a loop that never terminates (since changePort is a local parameter and nothing changes it inside the loop)

restart() is not stopping the existent server.

It is just going through the method again starting a new ServerSocket , with the old one still running.

Since the boolean changePort is true, it won't even go inside the while loop, and never accepts a client socket. On the other hand the old server socket is still happily running.

In order to get this working properly you need to use a proper class, instead of a bunch of static methods. Put things like the port number and the serverSocket as member variables. Then check those in your while loop, without calling the method again. Something like:

while (true) {
   this.serverSocket = new ServerSocket(this.portNum);

   try {   
     Socket client = server.accept();  

      //todo: do something with the client
   } 
   catch (IOException ex) { 
      //an IO error occurred, probably we were asked to restart
   }
}

Then you can have something like:

void restart(int portNum) {
  this.portNum = portNum;
  try {
    this.serverSocket.close();
  } catch (IOException ex) {
    //todo: handle it or log it somewhere
  }
}