在 IP 协议层,有多播、广播的概念。IP 地址分为网络地址和主机地址,主机地址全部为1,就是广播地址。多播使用 D 类地址,从 224.0.0.0 到 239.255.255.255。IP 多播需要 IGMP 的支持,大致是,需要接收多播的主机先向路由器进行注册,然后路由器在收到多播包后会转发给注册的主机。
java 语言实现多播、广播要用到 MulticastSocket,DatagramSocket。
多播发送:
package com.zhang; import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket; public class Multicast_Send {
public static void main(String[] args) {
String[] message = { "hello", "hi" };
int port = 1234; // 端口
InetAddress group = null; // 地址
MulticastSocket multicastSocket = null; // 组播套接字 try {
group = InetAddress.getByName("239.1.1.1"); // 设置多播地址
multicastSocket = new MulticastSocket(port);
// 设置数据包的ttl,值从0到255,应该是和ip包的ttl字段对应上了
// 之前设置为1,在无限局域网中,数据包无法到达其他主机,所以这里设为2
// 如果设为0,则只能发送给本机
multicastSocket.setTimeToLive(2);
multicastSocket.joinGroup(group);
} catch (Exception e) {
e.printStackTrace();
} while (true) {
try {
DatagramPacket packet = null;
for (String msg : message) // 循环发送每条广播信息
{
msg = msg + "," + System.currentTimeMillis();
byte buff[] = msg.getBytes();
packet = new DatagramPacket(buff, buff.length, group, port);
multicastSocket.send(packet);
System.out.println("send:" + msg);
Thread.sleep(2000);
}
} catch (Exception e) {
System.out.println("Error:" + e);
}
} }
}
多播接收:
package com.zhang; import java.net.DatagramPacket;
import java.net.InetAddress;
import java.net.MulticastSocket; public class Multicast_Recv {
public static void main(String[] args) throws Exception {
InetAddress group = InetAddress.getByName("239.1.1.1");
int port = 1234;
MulticastSocket socket = new MulticastSocket(port);
socket.joinGroup(group); while (true) {
byte buff[] = new byte[8192];
DatagramPacket packet = null;
packet = new DatagramPacket(buff, buff.length, group, port);
socket.receive(packet);
String message = new String(packet.getData(), 0, packet.getLength());
System.out.println("receive:" + message);
}
}
}
广播发送:
package com.zhang; import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress; public class Broadcast_Send {
public static void main(String[] args) {
// 本机ip:10.3.80.248, 子网掩码:255.255.255.0,推出广播地址:10.3.80.255
String host = "10.3.80.255"; // 广播地址
int port = 9999; // 广播的目的端口
String message = null; // 用于发送的字符串
try {
while (true) {
message = "hello world " + System.currentTimeMillis();
InetAddress addr = InetAddress.getByName(host);
DatagramSocket ds = new DatagramSocket();
DatagramPacket dp = new DatagramPacket(message.getBytes(),
message.length(), addr, port);
ds.send(dp);
Thread.sleep(2000);
// ds.close();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
广播接收:
package com.zhang; import java.net.DatagramPacket;
import java.net.DatagramSocket; public class Broadcast_Recv {
public static void main(String[] args) {
int port = 9999; // 开启监听的端口
DatagramSocket ds = null;
DatagramPacket dp = null;
byte[] buf = new byte[1024];// 存储发来的消息
try {
// 绑定端口
ds = new DatagramSocket(port);
dp = new DatagramPacket(buf, buf.length);
System.out.println("监听广播端口打开:"); while (true) {
ds.receive(dp);
System.out.println("收到广播消息:" + new String(buf));
} // ds.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}