局域网下UDP广播发送与接收

1.接收udp广播的线程

private void receiverUdpBroadCast(){
new Thread(new Runnable() {
@Override
public void run() {
byte[] buffer = new byte[1024];
MulticastSocket server = null;
try {
server = new MulticastSocket (port);
InetAddress ip = InetAddress.getByName(BROADCAST_IP);
server.joinGroup(ip);
final DatagramPacket packet = new DatagramPacket(buffer,buffer.length);
while(true){
try {
server.receive(packet);
final String s = new String(packet.getData(), 0, packet.getLength(), "UTF-8");
runOnUiThread(new Runnable() {
@Override
public void run() {
str.append("收到数据："+s+",address:"+packet.getAddress()+"\n");
//                                    Toast.makeText(MainActivity.this,"收到数据啦："+s,Toast.LENGTH_SHORT).show();
}
});
System.out.println("address : " + packet.getAddress() + ", port : " + packet.getPort() + ", content : " + s);
} catch (IOException e) {
e.printStackTrace();
}
}
} catch (SocketException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally{
if(server != null)
server.close();
}
}
}).start();
}

2.发送UDP广播线程

private void sendBroadCastToCenter(){
new Thread(new Runnable() {
@Override
public void run() {
WifiManager wifiMgr = (WifiManager)getApplicationContext().getSystemService(Context.WIFI_SERVICE);
WifiInfo wifiInfo = wifiMgr.getConnectionInfo();
/*这里获取了IP地址，获取到的IP地址还是int类型的。*/
int ip = wifiInfo.getIpAddress();
/*这里就是将int类型的IP地址通过工具转化成String类型的，便于阅读
String ips = Formatter.formatIpAddress(ip);
*/
/*这一步就是将本机的IP地址转换成xxx.xxx.xxx.255*/
int broadCastIP = ip | 0xFF000000;
Log.d("bbbb","broadCastIP:"+broadCastIP);
MulticastSocket theSocket = null;
try {
String ipAddress = Formatter.formatIpAddress(broadCastIP);
Log.d("bbbb","ipAddress:"+ipAddress);
InetAddress server = InetAddress.getByName(BROADCAST_IP);
theSocket = new MulticastSocket(port);
theSocket.joinGroup(server);
theSocket.setLoopbackMode(false);
String data = "Helloaaa";
DatagramPacket theOutput = new DatagramPacket(data.getBytes(), data.length(), server, port);
/*这一句就是发送广播了，其实255就代表所有的该网段的IP地址，是由路由器完成的工作*/
theSocket.send(theOutput);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (theSocket != null)
theSocket.close();
}
}
}).start();

}

实际开发中在同一局域网下，可每隔三秒可发一次udp包，接收线程先于发送线程启动