Android使用MulticastSocket实现多点广播图片 Android使用MulticastSocket实现多点广播图片

时间:2021-03-30 Knick_Zhang 人气:0

DatagramSocket只允许数据报发送给指定的目标地址，而MulticastSocket可以将数据报以广播的方式发送至多个客户端。其主要思想是设置一组特殊网络地址作为多点广播地址，每个多点广播地址都被看做一个组，当客户端需要发送，接收广播消息时，加入到该组即可。

IP协议为多点广播提供了这些特殊的IP地址，这些IP地址的范围是224.0.0.0至239.255.255.255。当MulticastSocket把一个DatagramPacket发送到多点广播IP地址时，该数据将被自动广播到加入该地址的所有MulticastSocket，同时也可以设置该MulticastSocket接收自身发送的数据。

如果仅仅是用于发送数据报的MulticastSocket对象，使用默认地址，随机端口即可。但如果创建接收用的MulticastSocket对象，则该MulticastSocket对象必须指定端口，否则发送方无法确定发送数据报的目标端口。

下面通过一个简单的例子实现多点广播图片：

多点广播的工具类：

public class ComUtil
{
 public static final String BROADCAST_IP = "224.2.2.2";
 public static final int BOADCAST_PORT = 30000;
 private static final int DATA_LEN = 100 * 1024;
 //定义本程序的MulticastSocket实例
 private MulticastSocket socket = null;
 //定义广播的IP地址
 private InetAddress broadcastAddress = null;
 //定义接收网络数据的字符数组
 byte[] inBuff = new byte[DATA_LEN];
 //以指定字节数组创建准备接受的DatagramPacket对象
 private DatagramPacket inPacket = new DatagramPacket(inBuff , inBuff.length);
 //定义一个用于发送的DatagramPacket对象
 private DatagramPacket outPacket = null;
 private Handler handler;

 //构造器，初始化资源
 public ComUtil(Handler handler) throws Exception
 {
 this.handler = handler;
 //因为该MultcastSocket对象需要接受数据，所以有指定端口
 socket = new MulticastSocket(BOADCAST_PORT);
 broadcastAddress = InetAddress.getByName(BROADCAST_IP);
 //将该socket加入指定的多点广播地址
 socket.joinGroup(broadcastAddress);
 //设置本MultcastSocket发送的数据报将被送到本身
 socket.setLoopbackMode(false);
 //初始化发送用的DatagramSocket，它包含一个长度为0的字节数组
 outPacket = new DatagramPacket(new byte[0] , 0 , broadcastAddress , BOADCAST_PORT);
 new ReadBroad().start();
 }

 //广播消息的工具方法
 public void broadCast(byte[] msg)
 {
 try
 {
  //将msg字符串转换为字节数组
  byte[] buff = msg;
  //设置发送用的DatagramPacket里的字节数组
  outPacket.setData(buff);
  //发送数据
  socket.send(outPacket);
 }
 catch (IOException e)
 {
  e.printStackTrace();
 }
 }

 //持续读取MulticastSocket的线程
 class ReadBroad extends Thread
 {
 public void run()
 {
  while (true)
  {
  try
  {
   //读取Socket中的数据
   socket.receive(inPacket);
   Message msg = new Message();
   msg.what = 0x123;
   msg.obj = inBuff;
   handler.sendMessage(msg);
  }
  catch (IOException e)
  {
   e.printStackTrace();
  }
  }
 }
 }
}

MainActivity类：

public class MainActivity extends Activity
{
 private Button button;
 private ImageView img;
 private ComUtil comUitl;
 Handler handler = new Handler()
 {
 @Override
 public void handleMessage(Message msg)
 {
  if (msg.what == 0x123)
  {
  byte[] result = (byte[]) msg.obj;
  img.setImageBitmap(BitmapFactory.decodeByteArray(result , 0 , result.length));
  }
 }
 };

 @Override
 protected void onCreate(Bundle savedInstanceState)
 {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.main_activity);
 try
 {
  comUitl = new ComUtil(handler);
 }
 catch (Exception e)
 {
  e.printStackTrace();
 }

 button = (Button) findViewById(R.id.send_img_all);
 img = (ImageView) findViewById(R.id.receiver_img);
 button.setOnClickListener(new View.OnClickListener()
 {
  @Override
  public void onClick(View view)
  {
  sendData();
  }
 });
 }

 private void sendData()
 {
 Bitmap bitmap = BitmapFactory.decodeResource(getResources() , R.drawable.wenqing2);
 ByteArrayOutputStream byteArray = new ByteArrayOutputStream();
 bitmap.compress(Bitmap.CompressFormat.PNG , 100 , byteArray);
 bitmap.recycle();
 final byte[] msg = byteArray.toByteArray();
 new Thread()
 {
  @Override
  public void run()
  {
  comUitl.broadCast(msg);
  }
 }.start();

 try
 {
  byteArray.close();
 }
 catch (IOException e)
 {
  e.printStackTrace();
 }
 }
}

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