多播

組播使用UDP對一定範圍內的地址傳送相同的一組Packet，即一次可以向多個接受者發出資訊，其與單播的主要區別是地址的形式。IP協議分配了一定範圍的地址空間給多播（多播只能使用這個範圍內的IP），IPv4中組播地址範圍為224.0.0.0到239.255.255.255

傳送端

package com.turing.mobilecontrol;

import java.io.IOException;
import java.io.OutputStream;
import java.net.DatagramPacket;
import java.net.InetAddress;
import
 
 java.net.MulticastSocket;
import java.net.Socket;
import java.net.UnknownHostException;

import android.os.AsyncTask;
import android.os.Handler;
import android.os.Message;

public class MobileSocketClient {
    private static MobileSocketClient mobileSocketClient = null;
    private static String BROADCAST_IP = "224.0.0.1"
 
;
    private static int BROADCAST_PORT = 9898;
    private static final String TAG = "MobileSocketClient";
    private MulticastSocket multicastSocket;
    private InetAddress inetAddress;
    private Handler handler;

    private MobileSocketClient() {
        try {
            //初始化組播
            inetAddress = InetAddress.getByName(BROADCAST_IP);
            multicastSocket = new
 
 MulticastSocket(BROADCAST_PORT);
            multicastSocket.setTimeToLive(1);
            multicastSocket.joinGroup(inetAddress);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void init(Handler handler) {
        this.handler = handler;
    }

    public static MobileSocketClient getInstance() {
        if (mobileSocketClient == null) {
            mobileSocketClient = new MobileSocketClient();
        }
        return mobileSocketClient;
    }

   //傳送資料
    public void send(final String content) {
        new AsyncTask<String, Integer, String>() {

            @Override
            protected String doInBackground(String... paramVarArgs) {
                byte[] data = paramVarArgs[0].getBytes();
                //構造要傳送的資料
                DatagramPacket dataPacket = new DatagramPacket(data,
                        data.length, inetAddress, BROADCAST_PORT);
                try {
                    multicastSocket.send(dataPacket);
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                    return App.getInstance().getResources()
                            .getString(R.string.send_failed);
                }
                return App.getInstance().getResources()
                        .getString(R.string.send_success);
            }

            @Override
            protected void onPostExecute(String result) {
                // TODO Auto-generated method stub
                super.onPostExecute(result);
                Message msg = new Message();
                msg.what = TuringHandler.STATUS;
                msg.obj = result;
                handler.sendMessage(msg);
            }
        }.execute(content);

    }

}

接收端

package com.tuling.demo.socket;

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

import android.os.Handler;
import android.os.Message;
import android.util.Log;

import com.tuling.demo.TuringHandler;

public class ServerSocket extends Thread {
    private static final String TAG = TuringServerSocket.class.getSimpleName()
            .toString();
    private static int BROADCAST_PORT = 9898;
    private static final String BROADCAST_IP = "224.0.0.1";
    private MulticastSocket multicastSocket;
    String content = "";
    private Handler handler;
    private InetAddress inetAddress;

    public TuringServerSocket(Handler handler) throws IOException {
        // 多播配置
        multicastSocket = new MulticastSocket(BROADCAST_PORT);
        inetAddress = InetAddress.getByName(BROADCAST_IP);
        multicastSocket.joinGroup(inetAddress);
        // handler
        this.handler = handler;
    }

    @Override
    public void run() {
        while (true) {
            Log.d(TAG, "run");
            byte buf[] = new byte[1024];
            DatagramPacket dp = new DatagramPacket(buf, buf.length,
                    inetAddress, BROADCAST_PORT);
            try {
                multicastSocket.receive(dp);
                String content = new String(buf, 0, dp.getLength());
                Message msg = new Message();
                msg.what = TuringHandler.RECEIVE_COMMOND;
                msg.obj = content;
                handler.sendMessage(msg);
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {

    }
}