UDP協(xié)議格式以及在java中的使用

UDP是面向無連接的通訊協(xié)議，由于通訊不需要連接，所以可以實(shí)現(xiàn)廣播發(fā)送。UDP通訊時(shí)不需要接收方確認(rèn)，屬于不可靠的傳輸，可能會(huì)出現(xiàn)丟包現(xiàn)象，實(shí)際應(yīng)用中要求程序員編程驗(yàn)證。

UDP適用于DNS、視頻音頻等多媒體通信、廣播通信（廣播、多播）。例如我們常用的QQ，就是一個(gè)以UDP為主，TCP為輔的通訊協(xié)議。

UDP報(bào)文格式如下：

UDP首部有8個(gè)字節(jié)，由4個(gè)字段構(gòu)成，每個(gè)字段都是兩個(gè)字節(jié)，

源端口：數(shù)據(jù)發(fā)送方的端口號(hào).

目的端口：數(shù)據(jù)接收方的端口號(hào)。

長度：UDP數(shù)據(jù)報(bào)的整個(gè)長度（包括首部和數(shù)據(jù)），其最小值為8（只有首部）。

校驗(yàn)和：檢測UDP數(shù)據(jù)報(bào)在傳輸中是否有錯(cuò)，有錯(cuò)則丟棄。

可以使用nc發(fā)送UDP數(shù)據(jù)包：echo hello | nc -uv 127.0.0.1 9999。

用tcpdump抓取到的數(shù)據(jù)包如下（注意先運(yùn)行tcpdump，然后再執(zhí)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. ... ...

說明：

• 源端口：0xb262，十進(jìn)制的45666。
• 目的端口：0x270f，十進(jìn)制的9999。
• 長度：0x000e，14個(gè)字節(jié)的報(bào)文長度。
• 校驗(yàn)和：0xfe21。

bio之單播

單播就是一對(duì)一通信。

服務(wù)器端代碼如下：

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);} }

客戶端代碼如下：

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()));} }

客戶端和服務(wù)端的代碼幾乎一致，只不過接收和發(fā)送數(shù)據(jù)的順序不一致，receive和send都?xì)W式阻塞方法。

bio之廣播

廣播：同一網(wǎng)段所有主機(jī)都能接收，前提是端口要開啟監(jiān)聽。

只需要將單播的例子中客戶端發(fā)送數(shù)據(jù)的IP修改為255.255.255.255即可，具體修改如下：

DatagramPacket datagramPacket = new DatagramPacket(req, req.length, new InetSocketAddress("255.255.255.255", 9999));

• 1

bio之多播（組播）

多播數(shù)據(jù)報(bào)套接字類用于發(fā)送和接收IP多播包。MulticastSocket是一種DatagramSocket，它具有加入Internet上其他多播主機(jī)的“組”的附加功能。

多播組通過D類IP地址和標(biāo)準(zhǔn)UDP端口號(hào)指定。D類IP地址在224.0.0.0和239.255.255.255的范圍內(nèi)。地址224.0.0.0被保留，不應(yīng)使用。

可以通過首先使用所需端口創(chuàng)建MulticastSocket，然后調(diào)用joinGroup(InetAddress groupAddr)方法來加入多播組。

服務(wù)器端代碼如下：

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);} }

客戶端代碼如下：

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實(shí)現(xiàn)單播

服務(wù)器端代碼如下：

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);} }

客戶端代碼如下：

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實(shí)現(xiàn)單播

服務(wù)器端代碼如下：

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 SimpleChannelInboundHandler<DatagramPacket>() {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, DatagramPacket msg) throws Exception {// 接收數(shù)據(jù)System.out.println(msg.content().toString(CharsetUtil.UTF_8));// 發(fā)送數(shù)據(jù)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();}} }

客戶端代碼如下：

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 SimpleChannelInboundHandler<DatagramPacket>() {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, DatagramPacket msg) throws Exception {// 接收數(shù)據(jù)System.out.println(msg.content().toString(CharsetUtil.UTF_8));ctx.close();}});Channel channel = bootstrap.bind(0).sync().channel();// 發(fā)送數(shù)據(jù)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("查詢超時(shí)");}} finally {group.shutdownGracefully();}} }

Netty實(shí)現(xiàn)廣播

只需要將netty實(shí)現(xiàn)的單播的客戶端代碼做如下修改：

增加option：

.option(ChannelOption.SO_BROADCAST, true)

• 1

將IP地址修改為廣播地址255.255.255.255：

channel.writeAndFlush(new DatagramPacket(Unpooled.copiedBuffer("hello server", CharsetUtil.UTF_8), new InetSocketAddress("255.255.255.255", 8899)));

• 1

底層實(shí)現(xiàn)

recvfrom負(fù)責(zé)接收UDP數(shù)據(jù)，其函數(shù)聲明如下：

ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen);

sendto負(fù)責(zé)發(fā)送UDP數(shù)據(jù)，其函數(shù)聲明如下：

ssize_t sendto(int sockfd, const void *buf, size_t len, int flags, const struct sockaddr *dest_addr, socklen_t addrlen);

• 下面通過對(duì)bio之單播的例子所產(chǎn)生的系統(tǒng)調(diào)用進(jìn)行跟蹤：

啟動(dòng)服務(wù)器端服務(wù)Server：

# strace -ff -o out java Server

然后使用nc命令充當(dāng)客戶端進(jìn)行連接：echo hello | nc -uv 127.0.0.1 9999。

產(chǎn)生的系統(tǒng)調(diào)用中關(guān)鍵信息如下：

socket(AF_INET6, SOCK_DGRAM, IPPROTO_IP) = 4 bind(4, {sa_family=AF_INET6, sin6_port=htons(9999), inet_pton(AF_INET6, "::", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, 28) = 0 recvfrom(4, "hello\n", 1024, 0, {sa_family=AF_INET6, sin6_port=htons(7361), inet_pton(AF_INET6, "::ffff:127.0.0.1", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, [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_family=AF_INET6, sin6_port=htons(7361), inet_pton(AF_INET6, "::ffff:127.0.0.1", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, 28) = 12

可見發(fā)送和接收數(shù)據(jù)確實(shí)使用了上面的系統(tǒng)調(diào)用，另外上面的系統(tǒng)調(diào)用中并沒有l(wèi)isten函數(shù)，不需要監(jiān)聽端口，再次驗(yàn)證UDP是面向無連接的。

總結(jié)

以上是生活随笔為你收集整理的【转】UDP协议格式以及在java中的使用的全部內(nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。