Java中的UDP广播

早上。

我是Java和套接字连接的新手，但我试图在端口8001上将255.255.255.255上的UDP数据包/广播发送到设备。 我可以将数据发送得很好，但是当接收数据时，连接超时。 我有一个数据包嗅探器，我可以看到数据包发送，然后设备响应。

我很确定这是我在代码中遗漏的一个新手错误，但我已经坚持了一段时间，任何帮助都会受到赞赏。

m_Socket = new DatagramSocket(m_SERVERPORT); InetAddress address = InetAddress.getByName(m_SERVERIP); m_DataPack = new DatagramPacket(m_SERVERCMD.getBytes(), m_SERVERCMD.getBytes().length, address, m_SERVERPORT); m_Socket.setBroadcast(true); m_Socket.connect(address, m_SERVERPORT); m_Socket.send(m_DataPack); m_DataPack = new DatagramPacket(data, data.length, address, m_SERVERPORT); m_Socket.receive(m_DataPack); // This is where it times out data = m_DataPack.getData(); String received = data.toString(); System.out.println("Received: " + received); m_Socket.close(); 

谢谢和Gig’Em。

编辑：

我不确定这是否有帮助但是当我观察m_Socket对象时，我可以在发送之前看到以下内容：

 bound = true; close = false; connectedAddress = Inet4Address (id = 32) (-1,-1,-1,-1); connectedPort = 8001; connectState = 1; created = true; impl = PlainDatagramSocketImpl; oldImpl = false; 

并且m_DataPack对象如下：

 address = Inet4Address (id = 32) (-1,-1,-1,-1); bufLength = 6 (size of packet I'm sending is 6 char long); offset = 0; port = 8001; 

Answer 1

这没有意义。 您正在广播，这是1对多，您也在连接，即1对1。 这是什么？

失去连接。 并输掉255.255.255.255。 这已被大约弃用了大约20年。 使用子网本地广播地址，例如192.168.1.255。

Answer 2

您还可以查看Broadcasting to Multiple Recipients中描述的MulticastSocket。 希望这可以帮助。

Answer 3

如果要接收数据报，则需要将bind（）绑定到本地端点（地址+端口）。

Answer 4

您正在同一设备上发送和接收数据包。 您可以分开发送和接收端口（例如，发送8001，接收8002）。 并将发送和接收代码作为单独的线程运行。 如果两个设备必须找到彼此（或一个设备找到自己）。

 import java.io.IOException; import java.net.*; 

接收：

 private DatagramSocket getReceiveSocket() throws UnknownHostException, SocketException { if (receiveSocket == null) { receiveSocket = new DatagramSocket(8002, InetAddress.getByName("0.0.0.0")); // 0.0.0.0 for listen to all ips receiveSocket.setBroadcast(true); } return receiveSocket; } public void receive() throws IOException { // Discovery request command byte[] buffer = "__DISCOVERY_REQUEST__".getBytes(); DatagramPacket packet = new DatagramPacket(buffer, buffer.length); getReceiveSocket().receive(packet); System.out.println("Discovery package received! -> " + packet.getAddress() + ":" + packet.getPort()); // Get received data String data = new String(packet.getData()).trim(); if (data.equals("__DISCOVERY_REQUEST__")) { // Check valid command // Send response byte[] response = new byte["__DISCOVERY_RESPONSE".length()]; DatagramPacket responsePacket = new DatagramPacket(response, response.length, packet.getAddress(), packet.getPort()); getReceiveSocket().send(responsePacket); System.out.println("Response sent to: " + packet.getAddress() + ":" + packet.getPort()); } else { System.err.println("Error, not valid package!" + packet.getAddress() + ":" + packet.getPort()); } } 

发送：

 private DatagramSocket getSendSocket() throws UnknownHostException, SocketException { if (sendSocket == null) { sendSocket = new DatagramSocket(8001, InetAddress.getLocalHost()); sendSocket.setBroadcast(true); } return sendSocket; } public void send() throws IOException { // Discovery request command byte[] data = "__DISCOVERY_REQUEST__".getBytes(); DatagramPacket packet = new DatagramPacket(data, data.length, InetAddress.getByName("255.255.255.255"), 8002); getSendSocket().send(packet); System.out.println("Discovery package sent!" + packet.getAddress() + ":" + packet.getPort()); // Discovery response command byte[] response = new byte["__DISCOVERY_RESPONSE__".length()]; DatagramPacket responsePacket = new DatagramPacket(response, response.length); getSendSocket().receive(responsePacket); System.out.println("Discovery response received!" + responsePacket.getAddress() + ":" + responsePacket.getPort()); String responseData = new String(responsePacket.getData()).trim(); if (responseData.equals("__DISCOVERY_RESPONSE__")) { // Check valid command System.out.println("Found buddy!" + responsePacket.getAddress() + ":" + responsePacket.getPort()); } } 

当然应该把这段代码放在一个线程的循环中。 基于此示例： https ： //demey.io/network-discovery-using-udp-broadcast/