http://blog.csdn.net/ghostyu/article/details/8182516
Android的Wifi，默认情况下是不接受组播的，见：http://developer.android.com/reference/android/net/wifi/WifiManager.MulticastLock.html
默认情况下，应用是不接收组播信息的，这样要接收处理的报文太多，很快就会把电池用尽。要知道移动设备（特指电话一类的，平板要好得多）目前最重要的因素是电量。
要想打开组播功能，有以下几个步骤：
- 在Manifest文件中加入：android.permission.CHANGE_WIFI_MULTICAST_STATE，这个权限
- 获取到MulticastLock对象，这个对象不能直接实例化，要通过WifiManager间接得到，工厂模式
- 调用MulticastLock对象的acquire方法，获取到组播锁
- 相应的，用完组播，为了不浪费电力，要调用MulticastLock的release方法释放锁
1、创建组播用的udp socket，
2、绑定组播地址为239.255.255.250，端口为3702，因为ws-discovery的组播地址和端口就是为239.255.255.250和3702
直接上代码：
public class MulticastDemoActivity extends Activity {
MulticastLock multicastLock;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
allowMulticast();
try {
NetUtil.findServerIpAddress();
} catch (IOException e) {
throw new RuntimeException(e);
}
Log.d("multicast.demo", "find ip ok.");
multicastLock.release();
}
private void allowMulticast(){
WifiManager wifiManager=(WifiManager)getSystemService(Context.WIFI_SERVICE);
multicastLock=wifiManager.createMulticastLock("multicast.test");
multicastLock.acquire();
}
}public class NetUtil {
private static final String TAG="Net.Utils";
private static final int MULTICAST_PORT=5111;
private static final String GROUP_IP="224.5.0.7";
private static byte[] sendData;
static{
sendData=new byte[4];
// 0xEE78F1FB
sendData[3] = (byte) 0xEE;
sendData[2] = (byte) 0×78;
sendData[1] = (byte) 0xF1;
sendData[0] = (byte) 0xFB;
}
public static String findServerIpAddress() throws IOException{
String ip=null;
MulticastSocket multicastSocket=new MulticastSocket(MULTICAST_PORT);
multicastSocket.setLoopbackMode(true);
InetAddress group = InetAddress.getByName(GROUP_IP);
multicastSocket.joinGroup(group);
DatagramPacket packet=new DatagramPacket(sendData, sendData.length,group,MULTICAST_PORT);
for(;;){
multicastSocket.send(packet);
Log.d(TAG,">>>send packet ok");
byte[] receiveData=new byte[256];
packet=new DatagramPacket(receiveData, receiveData.length);
multicastSocket.receive(packet);
String packetIpAddress=packet.getAddress().toString();
packetIpAddress=packetIpAddress.substring(1, packetIpAddress.length());
Log.d(TAG,"packet ip address: "+packetIpAddress);
StringBuilder packetContent=new StringBuilder();
for(int i=0;i<receiveData.length;i++){
if(receiveData[i]==0){
break;
}
packetContent.append((char)receiveData[i]);
}
ip=packetContent.toString();
Log.d(TAG,"packet content ip is: "+ip);
if(ip.equals(packetIpAddress)){
Log.d(TAG,"find server ip address: "+ip);
break;
}else{
Log.d(TAG,"not find server ip address, continue …");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
}
}
}
return ip;
}
} 上面代码供参考，但是没有测试在htc手机上成功
下面是本人修改过的代码：
public static String findServerIpAddress() throws IOException {
String sinfo = "";
byte[] sendData = sinfo.getBytes();
String ip = "";
try {
MulticastSocket multicastSocket = new MulticastSocket(
MULTICAST_PORT);
multicastSocket.setLoopbackMode(true);//修改添加代码部分不添加不能发送成功
InetAddress group = InetAddress.getByName(GROUP_IP);
multicastSocket.setLoopbackMode(true);
multicastSocket.joinGroup(group);
multicastSocket.setSoTimeout(10000);
DatagramPacket packet = new DatagramPacket(sendData,
sendData.length, group, MULTICAST_PORT);
for (;;) {
multicastSocket.send(packet);
Log.d(TAG, ">>>send packet ok");
byte[] receiveData = new byte[256];
packet = new DatagramPacket(receiveData, receiveData.length);
multicastSocket.receive(packet);
String packetIpAddress = packet.getAddress().toString();
packetIpAddress = packetIpAddress.substring(1,
packetIpAddress.length());
Log.d(TAG, "packet ip address: " + packetIpAddress);
StringBuilder packetContent = new StringBuilder();
for (int i = 0; i < receiveData.length; i++) {
if (receiveData[i] == 0) {
break;
}
packetContent.append((char) receiveData[i]);
}
ip = packetContent.toString();
Log.d(TAG, "packet content ip is: " + ip);
if (ip.equals(packetIpAddress)) {
Log.d(TAG, "find server ip address: " + ip);
break;
} else {
Log.d(TAG, "not find server ip address, continue …");
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
}
}
}
} catch (Exception ee) {
Log.d(TAG, ee.toString());
}
return ip;
}