来自 Java UDP 的空指针异常

Question

这是我的主要方法：

public void broadcastName(final String name, final InetAddress broadcastIP) {
    // Broadcasts the name of the device at a regular interval
    System.out.println("Broadcasting started!");
    Thread broadcastThread = new Thread(new Runnable() {

        @Override
        public void run() {
            try {
                String request = "ADD:"+name;
                byte[] message = request.getBytes();
                DatagramSocket socket = new DatagramSocket();
                socket.setBroadcast(true);
                DatagramPacket packet = new DatagramPacket(message, message.length, broadcastIP, BROADCAST_PORT);
                while(BROADCAST) {
                    System.out.println("socket: "+socket);
                    socket.send(packet);
                    System.out.println("Broadcast packet sent: " + packet.getAddress().toString());
                    Thread.sleep(BROADCAST_INTERVAL);
                }
                System.out.println("Broadcaster ending!");
                socket.disconnect();
                socket.close();
                return;
            }
            catch(SocketException e) {
                System.out.println("SocketException in broadcast: " + e);
                System.out.println("Broadcaster ending!");
                return;
            }
            catch(IOException e) {
                System.out.println("IOException in broadcast: " + e);
                System.out.println("Broadcaster ending!");
                return;
            }
            catch(InterruptedException e) {
                System.out.println("InterruptedException in broadcast: " + e);
                System.out.println("Broadcaster ending!");
                return;
            }
        }
    });
    broadcastThread.start();
}

当我在 while(BROADCAST) 行后立即到达 socket.send(packet) 时，我总是收到此错误。

Exception in thread "Thread-1" java.lang.NullPointerException: null address || null buffer
at java.net.DualStackPlainDatagramSocketImpl.send(Unknown Source)
at java.net.DatagramSocket.send(Unknown Source)
at application.ContactManager.run(ContactManager.java:103)
at java.lang.Thread.run(Unknown Source)

我检查确保套接字和数据包都不为空！还有什么可能是这里的罪魁祸首？

此错误消息背后的含义是什么？

编辑

我运行这段代码来自 Windows 笔记本电脑上的 Eclipse。我检索 IP 地址和设置 broadcastIP 的方式是这样的：

private static InetAddress getBroadcastIp() {
    // Function to return the broadcast address, based on the IP address of the device
    try {
        String addressString = InetAddress.getLocalHost().toString();
        InetAddress broadcastAddress = InetAddress.getByName(addressString);
        return broadcastAddress;
    }
    catch(UnknownHostException e) {
        System.out.println("UnknownHostException in getBroadcastIP: " + e);
        return null;
    }

}

Answer 1

把解决方案放在这里，正如@WayWay在评论中提到的：

当前代码在尝试获取 IP 地址时表现不正常，因为无法解析 .toString() 的结果，因此改为：

String addressString = InetAddress.getLocalHost().toString();
InetAddress broadcastAddress = InetAddress.getByName(addressString);

您应该尝试通过以下方式检索它：

InetAddress.getLocalHost().getHostAddress();

这样您将获得广播所需的正确InetAddress。

来自 Java UDP 的空指针异常

Null Pointer Exception from Java UDP

java

sockets

android

udp