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UDP是面向无连接的通讯协议#xff0c;由于通讯不需要连接#xff0c;所以可以实现广播发送。UDP通讯时不需要接收方确认#xff0c;属于不可靠的传输#xff0c;可能会出现丢包现象#xff0c;实际应用中要求程序员编程验证。
UDP适用于…UDP协议格式以及在java中的使用
UDP是面向无连接的通讯协议由于通讯不需要连接所以可以实现广播发送。UDP通讯时不需要接收方确认属于不可靠的传输可能会出现丢包现象实际应用中要求程序员编程验证。
UDP适用于DNS、视频音频等多媒体通信、广播通信广播、多播。例如我们常用的QQ就是一个以UDP为主TCP为辅的通讯协议。
UDP报文格式如下 UDP首部有8个字节由4个字段构成每个字段都是两个字节
源端口数据发送方的端口号.目的端口数据接收方的端口号。长度UDP数据报的整个长度包括首部和数据其最小值为8只有首部。校验和检测UDP数据报在传输中是否有错有错则丢弃。
可以使用nc发送UDP数据包echo hello | nc -uv 127.0.0.1 9999。
用tcpdump抓取到的数据包如下注意先运行tcpdump然后再执行nc命令
# tcpdump -i lo -X udp port 9999
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on lo, link-type EN10MB (Ethernet), capture size 262144 bytes
11:19:39.267912 IP localhost.45666 localhost.distinct: UDP, length 60x0000: 4500 0022 5914 4000 4011 e3b4 7f00 0001 E..Y.........0x0010: 7f00 0001 b262 270f 000e fe21 6865 6c6c .....b....!hell0x0020: 6f0a o.
... ...说明
源端口0xb262十进制的45666。目的端口0x270f十进制的9999。长度0x000e14个字节的报文长度。校验和0xfe21。
bio之单播
单播就是一对一通信。
服务器端代码如下
package com.morris.udp.bio.single;import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;public class Server {public static void main(String[] args) throws IOException {DatagramSocket datagramSocket new DatagramSocket(9999);byte[] bytes new byte[1024];DatagramPacket datagramPacket new DatagramPacket(bytes, bytes.length);datagramSocket.receive(datagramPacket);System.out.println(receive from client: new String(bytes));byte[] req hello client.getBytes();DatagramPacket resp new DatagramPacket(req, req.length, datagramPacket.getSocketAddress());datagramSocket.send(resp);}
}客户端代码如下
package com.morris.udp.bio.single;import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetSocketAddress;public class Client {public static void main(String[] args) throws IOException {DatagramSocket datagramSocket new DatagramSocket();byte[] req hello server.getBytes();DatagramPacket datagramPacket new DatagramPacket(req, req.length, new InetSocketAddress(127.0.0.1, 9999));datagramSocket.send(datagramPacket);datagramSocket.receive(datagramPacket);System.out.println(receive from server: new String(datagramPacket.getData()));}
}客户端和服务端的代码几乎一致只不过接收和发送数据的顺序不一致receive和send都欧式阻塞方法。
bio之广播
广播同一网段所有主机都能接收前提是端口要开启监听。
只需要将单播的例子中客户端发送数据的IP修改为255.255.255.255即可具体修改如下
DatagramPacket datagramPacket new DatagramPacket(req, req.length, new InetSocketAddress(255.255.255.255, 9999));1
bio之多播组播
多播数据报套接字类用于发送和接收IP多播包。MulticastSocket是一种DatagramSocket它具有加入Internet上其他多播主机的“组”的附加功能。
多播组通过D类IP地址和标准UDP端口号指定。D类IP地址在224.0.0.0和239.255.255.255的范围内。地址224.0.0.0被保留不应使用。
可以通过首先使用所需端口创建MulticastSocket然后调用joinGroup(InetAddress groupAddr)方法来加入多播组。
服务器端代码如下
package com.morris.udp.bio.multicast;import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.MulticastSocket;public class Server {public static void main(String[] args) throws IOException {InetAddress group InetAddress.getByName(228.5.6.7);MulticastSocket s new MulticastSocket(6789);s.joinGroup(group);byte[] buf new byte[1000];DatagramPacket recv new DatagramPacket(buf, buf.length);s.receive(recv);System.out.println(receive : new String(buf));s.leaveGroup(group);}
}客户端代码如下
package com.morris.udp.bio.multicast;import java.io.IOException;
import java.net.*;public class Client {public static void main(String[] args) throws IOException {String msg Hello;InetAddress group InetAddress.getByName(228.5.6.7);MulticastSocket s new MulticastSocket();s.joinGroup(group);DatagramPacket hi new DatagramPacket(msg.getBytes(), msg.length(), group, 6789);s.send(hi);s.leaveGroup(group);}
}NIO实现单播
服务器端代码如下
package com.morris.udp.nio;import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;public class Server {public static void main(String[] args) throws IOException {DatagramChannel datagramChannel DatagramChannel.open();datagramChannel.bind(new InetSocketAddress(9999));// datagramChannel.configureBlocking(false);ByteBuffer byteBuffer ByteBuffer.allocate(128);SocketAddress receive datagramChannel.receive(byteBuffer);byteBuffer.flip();byte[] bytes new byte[byteBuffer.remaining()];byteBuffer.get(bytes);System.out.println(receive from client: new String(bytes));byteBuffer.clear();byteBuffer.put(hello client.getBytes());datagramChannel.send(byteBuffer, receive);}
}客户端代码如下
package com.morris.udp.nio;import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.ByteBuffer;
import java.nio.channels.DatagramChannel;public class Client {public static void main(String[] args) throws IOException {DatagramChannel datagramChannel DatagramChannel.open();// datagramChannel.configureBlocking(false);String req hello server;ByteBuffer byteBuffer ByteBuffer.allocate(req.length());byteBuffer.put(req.getBytes());byteBuffer.flip();datagramChannel.send(byteBuffer, new InetSocketAddress(127.0.0.1, 9999));datagramChannel.receive(byteBuffer);byteBuffer.flip();byte[] bytes new byte[byteBuffer.remaining()];byteBuffer.get(bytes);System.out.println(receive from server: new String(bytes));}
}Netty实现单播
服务器端代码如下
package com.morris.udp.netty.single;import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOption;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.DatagramPacket;
import io.netty.channel.socket.nio.NioDatagramChannel;
import io.netty.util.CharsetUtil;public class Server {private static final int port 8899;public static void main(String[] args) throws InterruptedException {NioEventLoopGroup group new NioEventLoopGroup();try {Bootstrap bootstrap new Bootstrap();bootstrap.group(group).channel(NioDatagramChannel.class).handler(new SimpleChannelInboundHandlerDatagramPacket() {Overrideprotected void channelRead0(ChannelHandlerContext ctx, DatagramPacket msg) throws Exception {// 接收数据System.out.println(msg.content().toString(CharsetUtil.UTF_8));// 发送数据ctx.writeAndFlush(new DatagramPacket(Unpooled.copiedBuffer(hello client, CharsetUtil.UTF_8), msg.sender()));ctx.close();}});bootstrap.bind(port).sync().channel().closeFuture().await();} finally {group.shutdownGracefully();}}
}客户端代码如下
package com.morris.udp.netty.single;import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOption;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.DatagramPacket;
import io.netty.channel.socket.nio.NioDatagramChannel;
import io.netty.util.CharsetUtil;import java.net.InetSocketAddress;public class Client {public static void main(String[] args) throws InterruptedException {NioEventLoopGroup group new NioEventLoopGroup();try {Bootstrap bootstrap new Bootstrap();bootstrap.group(group).channel(NioDatagramChannel.class).handler(new SimpleChannelInboundHandlerDatagramPacket() {Overrideprotected void channelRead0(ChannelHandlerContext ctx, DatagramPacket msg) throws Exception {// 接收数据System.out.println(msg.content().toString(CharsetUtil.UTF_8));ctx.close();}});Channel channel bootstrap.bind(0).sync().channel();// 发送数据channel.writeAndFlush(new DatagramPacket(Unpooled.copiedBuffer(hello server, CharsetUtil.UTF_8), new InetSocketAddress(127.0.0.1, 8899)));if (!channel.closeFuture().await(30 * 1000)) {System.err.println(查询超时);}} finally {group.shutdownGracefully();}}
}Netty实现广播
只需要将netty实现的单播的客户端代码做如下修改
增加option
.option(ChannelOption.SO_BROADCAST, true)1
将IP地址修改为广播地址255.255.255.255
channel.writeAndFlush(new DatagramPacket(Unpooled.copiedBuffer(hello server, CharsetUtil.UTF_8), new InetSocketAddress(255.255.255.255, 8899)));1
底层实现
recvfrom负责接收UDP数据其函数声明如下
ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen);sendto负责发送UDP数据其函数声明如下
ssize_t sendto(int sockfd, const void *buf, size_t len, int flags, const struct sockaddr *dest_addr, socklen_t addrlen);下面通过对bio之单播的例子所产生的系统调用进行跟踪
启动服务器端服务Server
# strace -ff -o out java Server然后使用nc命令充当客户端进行连接echo hello | nc -uv 127.0.0.1 9999。
产生的系统调用中关键信息如下
socket(AF_INET6, SOCK_DGRAM, IPPROTO_IP) 4
bind(4, {sa_familyAF_INET6, sin6_porthtons(9999), inet_pton(AF_INET6, ::, sin6_addr), sin6_flowinfohtonl(0), sin6_scope_id0}, 28) 0
recvfrom(4, hello\n, 1024, 0, {sa_familyAF_INET6, sin6_porthtons(7361), inet_pton(AF_INET6, ::ffff:127.0.0.1, sin6_addr), sin6_flowinfohtonl(0), sin6_scope_id0}, [28]) 6
write(1, receive from client: hello\n\0\0\0\0\0..., 1045) 1045
write(1, \n, 1)
sendto(4, hello client, 12, 0, {sa_familyAF_INET6, sin6_porthtons(7361), inet_pton(AF_INET6, ::ffff:127.0.0.1, sin6_addr), sin6_flowinfohtonl(0), sin6_scope_id0}, 28) 12可见发送和接收数据确实使用了上面的系统调用另外上面的系统调用中并没有listen函数不需要监听端口再次验证UDP是面向无连接的。
