Java-重新加载类时关闭套接字

Question

So I'm working on a server for an IRC, and I added a config screen where you can edit the port it is using, but I have to reintialize the Listen class for it to take effect, so I have this in my Config class:

Listen.closePorts();
new Listen();

And here is my Listen class:

package server.network;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.ServerSocket;
import java.net.Socket;

import server.Server;
import server.gui.GUIMain;

public class Listen {
    private static Socket socket = null;
    private int port;

    public Listen() {
        try {
            port = Server.listenPort;
            @SuppressWarnings("resource")
            ServerSocket serverSocket = new ServerSocket(port);
            GUIMain.jta.append("\nServer Started and listening for messages on port " + port + ".\n");

            while(true) {
                socket = serverSocket.accept();
                InputStream is = socket.getInputStream();
                InputStreamReader isr = new InputStreamReader(is);
                BufferedReader br = new BufferedReader(isr);
                String msg = br.readLine();
                GUIMain.jta.append("Received message from client: " + msg + "\n");
            }
        } catch (Exception e) {
            GUIMain.jta.append("Port " + port + " already in use!\n");
        } finally {
            try {
                socket.close();
            }  catch(Exception e) { }
        }
    }

    public static void closePorts() {
        try {
            socket.close();
            GUIMain.jta.append("Server closed\n");
        } catch (IOException e) { }
    }
}

When I start the application it runs this class, opening the socket with the port specified, but when I try to close the port here:

public static void closePorts() {
    try {
        socket.close();
        GUIMain.jta.append("Server closed\n");
    } catch (IOException e) { }
}

It hangs on socket.close();

And if I comment Listen.closePorts(); out and try to reload the class and leaving the socket open it either hangs or runs the catch() if the port is the same as the port that is in use.

So long story short, How can I close the socket before reintalizing the class and use the new port?

Here's the full exception it trows:

java.lang.NullPointerException
    at server.network.Listen.closePorts(Listen.java:44)
    at server.gui.GUISettings.actionPerformed(GUISettings.java:86)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

Not providing a direct solution but no exceptions are thrown because your code is swallowing them all. Empty catch blocks are never good practice. At the very least, print the stack trace of the caught exception using e.printStackTrace()

Answer 2

The socket variable is not assigned until after a client makes a request. If you call closePorts() before that happens, your program will still be waiting at socket = serverSocket.accept(); and socket.close() will throw a NullPointerException because socket will still be null.

See http://docs.oracle.com/javase/7/docs/api/java/net/ServerSocket.html#accept() for a description of ServerSocket.accept().

Answer 3

There is no class reloading here, and you don't need to close the existing client's accepted sockets. Just close the ServerSocket and recreate it on the new port.