Android UDP 广播

2019-07-08 遇到的一点小问题
最近做局域网内Android端发UDP广播出去，然后接收服务器返回的信息。
参考的文章 Android UDP 广播实践，要用的都有写。

private final static String BROADCAST_IP = "255.255.255.255";       //广播范围
private final static int BROADCAST_PORT = 8888;     //端口
DatagramSocket socket = new DatagramSocket(BROADCAST_PORT);

发送

byte[] sendBuf = 发送内容.getBytes();
InetAddress address = InetAddress.getByName(BROADCAST_IP);
DatagramPacket sendPacket = new DatagramPacket(sendBuf, sendBuf.length, address, BROADCAST_PORT);
socket.send(sendPacket);
 socket.setBroadcast(true);

接收

byte[] ackBuf = new byte[1024];
InetAddress address = InetAddress.getByName(BROADCAST_IP);
DatagramPacket ackPacket = new DatagramPacket(ackBuf, ackBuf.length, address, BROADCAST_PORT);
socket.receive(ackPacket);
接收内容 = new String(ackPacket.getData(), 0, ackPacket.getLength());
应答的IP = ackPacket.getAddress().getHostAddress();

能收到udp消息，但有可能出现不在同一个广播地址，无法http沟通的情况，所以顺便查了下当前设备的广播地址，和服务器的比对。

/**
 * 获取当前移动设备的广播地址
 * 返回示例：192.168.11.255
 */
private String getPhoneBroadcast() throws SocketException {
    System.setProperty("java.net.preferIPv4Stack", "true");
    for (Enumeration<NetworkInterface> niEnum = NetworkInterface.getNetworkInterfaces(); niEnum.hasMoreElements(); ) {
        NetworkInterface ni = niEnum.nextElement();
        if (!ni.isLoopback()) {
            for (InterfaceAddress interfaceAddress : ni.getInterfaceAddresses()) {
                if (interfaceAddress.getBroadcast() != null) {
                    return interfaceAddress.getBroadcast().toString().substring(1);
                }
            }
        }
    }
    return null;
}