java.net.BindException：地址已在使用中(绑定失败)

我正在用JavaFX编写一个邮箱应用程序，使用MVC架构. 服务器的启动方法是这样的.

    @Override
    public void run() {
        try {
            serverSocket = new ServerSocket(PORT);
            controller.logEvent(Protocol.SERVER_STARTED, true, null, null);
            loadAccounts();
            while (isRunning.get()) {
                try {
                    Socket socket = serverSocket.accept();
                    if (isRunning.get()) {
                        connectedClients.add(socket);
                        Thread thread = new Thread(() -> {
                            handleClient(socket);
                            connectedClients.remove(socket);
                        });
                        thread.start();
                    } else {
                        socket.close();
                    }
                } catch (SocketException e) {
                    if (!isRunning.get()) {
                        break;
                    } else {
                        throw e;
                    }
                }
            }
        } catch (IOException e) {
            controller.logEvent(Protocol.SERVER_STARTED, false, null, null);
            e.printStackTrace();
        }
    }

而要停止服务器的是这样的:

    public void stopServer() {
        isRunning.set(false);
        try {
            if (serverSocket != null) {
                serverSocket.setReuseAddress(true);
                serverSocket.close();
                controller.logEvent(Protocol.SERVER_STOPPED, true, null, null);
                for (Socket socket : connectedClients) {
                    socket.close();
                }
                connectedClients.clear();
            }
        } catch (IOException e) {
            controller.logEvent(Protocol.SERVER_STOPPED, false, null, null);
            e.printStackTrace();
        }
    }

我的问题是服务器重启.当我试图重新启动它时，它会给我以下错误:

java.net.BindException: Address already in use (Bind failed)
    at java.base/java.net.PlainSocketImpl.socketBind(Native Method)
    at java.base/java.net.AbstractPlainSocketImpl.bind(AbstractPlainSocketImpl.java:452)
    at java.base/java.net.ServerSocket.bind(ServerSocket.java:395)
    at java.base/java.net.ServerSocket.<init>(ServerSocket.java:257)
    at java.base/java.net.ServerSocket.<init>(ServerSocket.java:149)
    at MailServer.run(MailServer.java:71)
    at java.base/java.lang.Thread.run(Thread.java:829)

我重新启动服务器的方法如下:

    public void startServer() {
        try {
            if (serverSocket != null && !serverSocket.isClosed()) {
                serverSocket.setReuseAddress(true);
                serverSocket.close();
            }
            isRunning.set(true);
            serverSocket = new ServerSocket(PORT);
            Thread thread = new Thread(this);
            thread.start();
            controller.logEvent(Protocol.SERVER_STARTED, true, null, null);
        } catch (IOException e) {
            controller.logEvent(Protocol.SERVER_STARTED, false, null, null);
        }
    }

你有什么建议来解决我的问题吗？我发现问题在于服务器停止时端口没有被释放，但我不知道如何修复它.