Java - 重新加载类时关闭套接字

Question

所以我正在为 IRC 开发服务器，我添加了一个配置屏幕，您可以在其中编辑它正在使用的端口，但我必须重新初始化 Listen 类才能使其生效，所以我有这在我的 Config 类中：

Listen.closePorts();
new Listen();

这是我的听课：

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) { }
    }
}

当我启动应用程序时，它运行这个类，打开指定端口的套接字，但是当我尝试在此处关闭端口时：

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

它挂在socket.close();

如果我将Listen.closePorts(); 注释掉并尝试重新加载类并保持套接字打开，如果端口与正在使用的端口相同，它要么挂起要么运行catch()。

长话短说，如何在重新初始化类并使用新端口之前关闭套接字？

这是它引发的完整异常：

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

不提供直接解决方案，但不会引发异常，因为您的代码正在吞噬它们。空的 catch 块从来都不是好习惯。至少，使用 e.printStackTrace() 打印捕获的异常的堆栈跟踪

Answer 2

socket 变量直到客户端发出请求后才被分配。如果您在此之前调用closePorts()，您的程序仍将在socket = serverSocket.accept(); 等待，而socket.close() 将抛出NullPointerException，因为socket 仍将为null。

有关 ServerSocket.accept() 的说明，请参阅 http://docs.oracle.com/javase/7/docs/api/java/net/ServerSocket.html#accept()。

Answer 3

这里没有类重新加载，你不需要关闭现有客户端接受的套接字。只需关闭 ServerSocket 并在新端口上重新创建它。