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();

}

}

}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。