Android上UDP组播无法接收数据的问题

　　最近,想做一个跨平台的局域网的文件传输软件,思路是组播设备信息,TCP连接传输文件。于是进行了一次简单的UDP组播测试，发现Android对于UDP组播接收数据的支持即极为有限。

部分代码如下

 package com.hsocket.Udp;

 import java.io.IOException;
 import java.net.DatagramPacket;
 import java.net.DatagramSocket;

 public class UdpReceiver {
     protected DatagramSocket client=null;
     private OnReceiveListener mOnReceiveListener=null;
     private Thread thrRecv=null;
     protected int port=0;
     public UdpReceiver(int port){
         this.port=port;
     }
     protected DatagramSocket Create() throws IOException{
         return new DatagramSocket(this.port);
     }
     public void addOnReceiveListener(OnReceiveListener mOnReceiveListener){
         this.mOnReceiveListener=mOnReceiveListener;
     }
     public void Stop(){
         if(this.thrRecv!=null) this.thrRecv.interrupt();
         this.Close();
     }
     public void Listen() throws IOException{
         this.Close();
         this.client=this.Create();
         if(this.thrRecv!=null) this.thrRecv.interrupt();
         this.thrRecv=new Thread(new Runnable() {
             @Override
             public void run() {
                 while(!Thread.interrupted()){
                     ReceiveEventArgs args=new ReceiveEventArgs();
                     try {
                         DatagramPacket packet=UdpReceiver.this.Receive();
                         args.Address=packet.getAddress();
                         args.Result=packet.getData();
                         args.Length=packet.getLength();
                         args.Error=false;
                     } catch (IOException e) {
                         e.printStackTrace();
                         args.Exception=e;
                         args.Error=true;
                     }
                     UdpReceiver.this.OnReceive(args);
                     if(UdpReceiver.this.mOnReceiveListener!=null)
                         UdpReceiver.this.mOnReceiveListener.OnReceive(UdpReceiver.this, args);
                 }
             }
         });
         this.thrRecv.start();
     }
     protected DatagramPacket Receive() throws IOException{
         byte[] recvBuf = new byte[4096];
         DatagramPacket recvPacket= new DatagramPacket(recvBuf , recvBuf.length);
         this.client.receive(recvPacket);
         return recvPacket;
     }
     protected void Close(){
         if(this.client!=null) this.client.close();
     }
     protected void OnReceive(ReceiveEventArgs args){

     }
 }

 package com.hsocket.Udp;

 import java.io.IOException;
 import java.net.DatagramSocket;
 import java.net.InetAddress;
 import java.net.MulticastSocket;

 public class UdpMultcastReceiver extends UdpReceiver {

     private InetAddress multicastAddr=null;
     public UdpMultcastReceiver(InetAddress multicastAddr,int port) {
         super(port);
         this.multicastAddr=multicastAddr;
     }

     @Override
     protected DatagramSocket Create() throws IOException {
         MulticastSocket socket=new MulticastSocket(this.port);
         socket.joinGroup(this.multicastAddr);
         socket.setLoopbackMode(false);
         return socket;
     }
 }

　　发现UDP组播接收数据在部分机型存在问题，与系统有极大关系。小米、华为的手机的深度定制系统对UDP的封杀极为严重。

　　首先是组播锁,Android的Wifi，默认情况下是不接受组播的，详见：http://developer.android.com/reference/android/net/wifi/WifiManager.MulticastLock.html

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

WifiManager wifiManager=(WifiManager)getSystemService(Context.WIFI_SERVICE);
        multicastLock=wifiManager.createMulticastLock("multicast.test");
        multicastLock.acquire();

　　其次，即使获取到组播锁，但部分机型依旧无法接收到广播，因为部分Android手机有多网卡，默认是本地回环网卡，IP为127.0.0.1，无法加入组播，需用MulticastSocket::setNetworkInterface来设置组播网卡

mMulticastSocket.setNetworkInterface(NetworkInterface.getByName("wlan0"));