阿里p9详解UDP协议格式及在Java的使用

港控/mmm° 2022-11-13 14:29 221阅读 0赞

**这篇文章主要介绍了UDP协议格式及在java中的使用,本文给大家介绍的非常详细，对大家的学习或工作具有一定的参考借鉴价值，需要的朋友可以参考下**  
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**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: 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 6
        0x0000: 4500 0022 5914 4000 4011 e3b4 7f00 0001 E.."Y.@.@.......
        0x0010: 7f00 0001 b262 270f 000e fe21 6865 6c6c .....b'....!hell
        0x0020: 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：0x000e，14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``));`
    [](javascript:; "全选")[](javascript:; "")

**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 SimpleChannelInboundHandler<DatagramPacket>() {
        
       @Override
       protected 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 SimpleChannelInboundHandler<DatagramPacket>() {
        
       @Override
       protected 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：**

**1.增加option：**

.option(ChannelOption.SO_BROADCAST, true)

**2.将IP地址修改为广播地址255.255.255.255：**

channel.writeAndFlush(new DatagramPacket(Unpooled.copiedBuffer("hello 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：**

ocket(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。**

**到此这篇关于详解UDP协议格式及在java中的使用的文章就介绍到这了,更多相关java中使用UDP协议内容请关注小编以前的文章或继续浏览下面的相关文章希望大家以后多多支持小编！**

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