三. Netty 进阶

1. 粘包与半包

1.1 粘包现象

服务端代码

@Slf4j
public class HelloWorldServer {void start() {NioEventLoopGroup boss = new NioEventLoopGroup(1);NioEventLoopGroup worker = new NioEventLoopGroup();try {ServerBootstrap serverBootstrap = new ServerBootstrap();serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.group(boss, worker);serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("connected {}", ctx.channel());super.channelActive(ctx);}@Overridepublic void channelInactive(ChannelHandlerContext ctx) throws Exception {log.debug("disconnect {}", ctx.channel());super.channelInactive(ctx);}});}});ChannelFuture channelFuture = serverBootstrap.bind(8080);log.debug("{} binding...", channelFuture.channel());channelFuture.sync();log.debug("{} bound...", channelFuture.channel());channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("server error", e);} finally {boss.shutdownGracefully();worker.shutdownGracefully();log.debug("stoped");}}public static void main(String[] args) {new HelloWorldServer().start();}
}

客户端代码

客户端代码希望发送 10 个消息，每个消息是 16 字节

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import lombok.extern.slf4j.Slf4j;@Slf4j
public class HelloWorldClient {public static void main(String[] args) {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connected...");ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {// 会在连接 channel 建立成功之后，会触发 active事件@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");for (int i = 0; i < 10; i++) {ByteBuf buffer = ctx.alloc().buffer();buffer.writeBytes(new byte[]{0, 1, 2, 3, 4,5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15});ctx.writeAndFlush(buffer);}}});}});ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}

服务器端的某次输出，可以看到一次就接收了 160 个字节，而非分 10 次接收。而我们客户端是发了10次，每次16字节，这就是粘包现象。

// 客户端输出
/*
11:57:47 [DEBUG] [nioEventLoopGroup-2-1] c.z.a.HelloWorldClient - connetted...
11:57:47 [DEBUG] [nioEventLoopGroup-2-1] c.z.a.HelloWorldClient - sending...
*/// 服务器端输出
/*
11:57:08 [DEBUG] [main] c.z.a.HelloWorldServer - [id: 0x6e5efdad] binding...
11:57:08 [DEBUG] [main] c.z.a.HelloWorldServer - [id: 0x6e5efdad, L:/0:0:0:0:0:0:0:0:8080] bound...
11:57:47 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xfaf43bd5, L:/127.0.0.1:8080 - R:/127.0.0.1:65248] REGISTERED
11:57:47 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xfaf43bd5, L:/127.0.0.1:8080 - R:/127.0.0.1:65248] ACTIVE
11:57:47 [DEBUG] [nioEventLoopGroup-3-1] c.z.a.HelloWorldServer - connected [id: 0xfaf43bd5, L:/127.0.0.1:8080 - R:/127.0.0.1:65248]
11:57:47 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xfaf43bd5, L:/127.0.0.1:8080 - R:/127.0.0.1:65248] READ: 160B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000010| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000020| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000030| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000040| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000050| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000060| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000070| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000080| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000090| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
+--------+-------------------------------------------------+----------------+
11:57:47 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xfaf43bd5, L:/127.0.0.1:8080 - R:/127.0.0.1:65248] READ COMPLETE*/

1.2 半包现象

服务端代码

只添加serverBootstrap.option(ChannelOption.SO_RCVBUF, 10);这一行代码

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;@Slf4j
public class HelloWorldServer {void start() {NioEventLoopGroup boss = new NioEventLoopGroup(1);NioEventLoopGroup worker = new NioEventLoopGroup();try {ServerBootstrap serverBootstrap = new ServerBootstrap();// 为现象明显，服务端修改一下接收缓冲区，其它代码不变// （调整系统的接收缓冲区-即滑动窗口）serverBootstrap.option(ChannelOption.SO_RCVBUF, 10);serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.group(boss, worker);serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("connected {}", ctx.channel());super.channelActive(ctx);}@Overridepublic void channelInactive(ChannelHandlerContext ctx) throws Exception {log.debug("disconnect {}", ctx.channel());super.channelInactive(ctx);}});}});ChannelFuture channelFuture = serverBootstrap.bind(8080);log.debug("{} binding...", channelFuture.channel());channelFuture.sync();log.debug("{} bound...", channelFuture.channel());channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("server error", e);} finally {boss.shutdownGracefully();worker.shutdownGracefully();log.debug("stoped");}}public static void main(String[] args) {new HelloWorldServer().start();}
}

客户端代码

客户端没有任何代码变动

@Slf4j
public class HelloWorldClient {public static void main(String[] args) {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connected...");ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {// 会在连接 channel 建立成功之后，会触发 active事件@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");for (int i = 0; i < 10; i++) {ByteBuf buffer = ctx.alloc().buffer();buffer.writeBytes(new byte[]{0, 1, 2, 3, 4,5, 6, 7, 8, 9,10, 11, 12, 13, 14, 15});ctx.writeAndFlush(buffer);}}});}});ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}

输出如下，可以看到客户端发了10次，每次16字节的消息，但是服务端分几次接受了36B、50B、50B、24B加起来共160字节。

（只要是使用TCP协议，那就会出现粘包和半包问题）

// 客户端输出
/*
12:10:42 [DEBUG] [nioEventLoopGroup-2-1] c.z.a.HelloWorldClient - connected...
12:10:42 [DEBUG] [nioEventLoopGroup-2-1] c.z.a.HelloWorldClient - sending...
*/// 服务端输出
/*
12:10:32 [DEBUG] [main] c.z.a.HelloWorldServer - [id: 0xdafb9db3] binding...
12:10:32 [DEBUG] [main] c.z.a.HelloWorldServer - [id: 0xdafb9db3, L:/0:0:0:0:0:0:0:0:8080] bound...
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] REGISTERED
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] ACTIVE
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] c.z.a.HelloWorldServer - connected [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450]
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ: 36B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000010| 00 01 02 03 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f |................|
|00000020| 00 01 02 03                                     |....            |
+--------+-------------------------------------------------+----------------+
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ COMPLETE
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ: 50B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000010| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000020| 04 05 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 |................|
|00000030| 04 05                                           |..              |
+--------+-------------------------------------------------+----------------+
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ COMPLETE
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ: 50B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 04 05 |................|
|00000010| 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 04 05 |................|
|00000020| 06 07 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 04 05 |................|
|00000030| 06 07                                           |..              |
+--------+-------------------------------------------------+----------------+
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ COMPLETE
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ: 24B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 08 09 0a 0b 0c 0d 0e 0f 00 01 02 03 04 05 06 07 |................|
|00000010| 08 09 0a 0b 0c 0d 0e 0f                         |........        |
+--------+-------------------------------------------------+----------------+
12:10:42 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ COMPLETE
12:12:26 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] READ COMPLETE
12:12:26 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x07aed482, L:/127.0.0.1:8080 - R:/127.0.0.1:65450] EXCEPTION: java.io.IOException: 远程主机强迫关闭了一个现有的连接。*/

注意

serverBootstrap.option(ChannelOption.SO_RCVBUF, 10) 影响的底层接收缓冲区（即滑动窗口）大小，仅决定了 netty 读取的最小单位，netty 实际每次读取的一般是它的整数倍

1.3 现象分析

粘包

• 现象，发送 abc def，接收 abcdef

• 原因

  • 应用层（应用层面）：接收方 ByteBuf 设置太大（Netty 默认 1024）
  • 滑动窗口（TCP层面）：假设发送方 256 bytes 表示一个完整报文，但由于接收方处理不及时且窗口大小足够大，这 256 bytes 字节就会缓冲在接收方的滑动窗口中，当滑动窗口中缓冲了多个报文就会粘包
  • Nagle 算法（TCP层面）：会造成粘包（因为报文头也占据一定的大小，如果携带的实际数据较小，那显然不划算，因此会攒够了一批量数据，然后发送过去，因此也会造成粘包）

半包

• 现象，发送 abcdef，接收 abc def
• 原因
  • 应用层（应用层面）：接收方 ByteBuf 小于实际发送数据量
  • 滑动窗口（TCP层面）：假设接收方的窗口只剩了 128 bytes，发送方的报文大小是 256 bytes，这时放不下了，只能先发送前 128 bytes，等待 ack 后才能发送剩余部分，这就造成了半包
  • MSS 限制（链路层面）：当发送的数据超过 MSS 限制后，会将数据切分发送，就会造成半包

本质是因为 TCP 是流式协议，消息无边界

缘由

滑动窗口

• TCP 以一个段（segment）为单位，每发送一个段就需要进行一次确认应答（ack）处理，但如果这么做，缺点是包的往返时间越长性能就越差（因为tcp协议是可靠的传输协议，因此需要保证1次请求1次应答，但是如果等到上一次请求得到应答，再发送下一次请求，那效率显然就很低，因此下面引入了滑动窗口来解决这个问题）

  [外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-leJ1X8om-1690552927974)(assets/0049.png)]

• 为了解决此问题，引入了窗口概念，窗口大小即决定了无需等待应答而可以继续发送的数据最大值

  [外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-c4Pwo8wB-1690552927976)(assets/0051.png)]

• 窗口实际就起到一个缓冲区的作用，同时也能起到流量控制的作用

  • 图中深色的部分即要发送的数据，高亮的部分即窗口

• 窗口内的数据才允许被发送，当应答未到达前，窗口必须停止滑动

• 如果 1001~2000 这个段的数据 ack 回来了，窗口就可以向前滑动

• 接收方也会维护一个窗口，只有落在窗口内的数据才能允许接收

MSS 限制

• 链路层对一次能够发送的最大数据有限制，这个限制称之为 MTU（maximum transmission unit），不同的链路设备的 MTU 值也有所不同，例如

• 以太网的 MTU 是 1500

• FDDI（光纤分布式数据接口）的 MTU 是 4352

• 本地回环地址的 MTU 是 65535 - 本地测试不走网卡

• MSS 是最大段长度（maximum segment size），它是 MTU 刨去 tcp 头和 ip 头后剩余能够作为数据传输的字节数

• ipv4 tcp 头占用 20 bytes，ip 头占用 20 bytes，因此以太网 MSS 的值为 1500 - 40 = 1460

• TCP 在传递大量数据时，会按照 MSS 大小将数据进行分割发送

• MSS 的值在三次握手时通知对方自己 MSS 的值，然后在两者之间选择一个小值作为 MSS

Nagle 算法

• 即使发送一个字节，也需要加入 tcp 头和 ip 头，也就是总字节数会使用 41 bytes，非常不经济。因此为了提高网络利用率，tcp 希望尽可能发送足够大的数据，这就是 Nagle 算法产生的缘由
• 该算法是指发送端即使还有应该发送的数据，但如果这部分数据很少的话，则进行延迟发送
  • 如果 SO_SNDBUF 的数据达到 MSS，则需要发送
  • 如果 SO_SNDBUF 中含有 FIN（表示需要连接关闭）这时将剩余数据发送，再关闭
  • 如果 TCP_NODELAY = true，则需要发送
  • 已发送的数据都收到 ack 时，则需要发送
  • 上述条件不满足，但发生超时（一般为 200ms）则需要发送
  • 除上述情况，延迟发送

1.4 解决方案

1. 短链接，发一个包建立一次连接，这样连接建立到连接断开之间就是消息的边界，缺点效率太低
2. 每一条消息采用固定长度，缺点浪费空间
3. 每一条消息采用分隔符，例如 \n，缺点需要转义
4. 每一条消息分为 head 和 body，head 中包含 body 的长度

方法1，短链接

以解决粘包为例

public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);public static void main(String[] args) {// 分 10 次发送for (int i = 0; i < 10; i++) {send();}}private static void send() {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("conneted...");ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");ByteBuf buffer = ctx.alloc().buffer();buffer.writeBytes(new byte[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15});ctx.writeAndFlush(buffer);// 发完即关ctx.channel().close();}});}});ChannelFuture channelFuture = bootstrap.connect("localhost", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}

输出，略

半包用这种办法还是解决不了，因为接收方的缓冲区大小是有限的（可再服务端通过如下方式调整netty的接收缓冲区，查看还是会出现半包现象：serverBootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR, new AdaptiveRecvByteBufAllocator(16, 16, 16));

方法2，固定长度

客户端的操作就是一次发送一个100字节长度的消息, 其中每10个字节表示一条消息（不够10个字节的补位，凑够10个字节）

服务端使用定长解码器，每10个字节，凑够1条消息，才给到下一个handler

客户端代码

@Slf4j
public class HelloWorldClient {public static void main(String[] args) {send();}private static void send() {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {// 会在连接 channel 建立成功之后，会触发 active事件@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {/*这里的操作就是发送一个100字节长度的消息, 其中每10个字节表示一条消息*/ByteBuf buf = ctx.alloc().buffer();char c = '0';Random r = new Random();for (int i = 0; i < 10; i++) {byte[] bytes = fill10Bytes(c, r.nextInt(10) + 1);c++;buf.writeBytes(bytes);}ctx.writeAndFlush(buf);}});}});ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}// 填够10个字节public static byte[] fill10Bytes(char c, int len) {byte[] bytes = new byte[10];Arrays.fill(bytes, (byte) '_');for (int i = 0; i < len; i++) {bytes[i] = (byte) c;}System.out.println(new String(bytes));return bytes;}
}

服务端代码

@Slf4j
public class HelloWorldServer {void start() {NioEventLoopGroup boss = new NioEventLoopGroup(1);NioEventLoopGroup worker = new NioEventLoopGroup();try {ServerBootstrap serverBootstrap = new ServerBootstrap();// 为现象明显，服务端修改一下接收缓冲区，其它代码不变// (调整系统的接收缓冲区（即滑动窗口）)// serverBootstrap.option(ChannelOption.SO_RCVBUF, 10);// 调整netty的接收缓冲区// serverBootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR,//                             new AdaptiveRecvByteBufAllocator(16, 16, 16));serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.group(boss, worker);serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {// 注意顺序: 要先添加定长的解码处理器, 再添加日志处理器ch.pipeline().addLast(new FixedLengthFrameDecoder(10));ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));}});ChannelFuture channelFuture = serverBootstrap.bind(8080);log.debug("{} binding...", channelFuture.channel());channelFuture.sync();log.debug("{} bound...", channelFuture.channel());channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("server error", e);} finally {boss.shutdownGracefully();worker.shutdownGracefully();log.debug("stoped");}}public static void main(String[] args) {new HelloWorldServer().start();}
}

客户端输出，可以看到客户端输出，一次写入了100个字节

Connected to the target VM, address: '127.0.0.1:50935', transport: 'socket'
13:51:29 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xdc9dffac] REGISTERED
13:51:29 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xdc9dffac] CONNECT: /127.0.0.1:8080
13:51:29 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xdc9dffac, L:/127.0.0.1:50973 - R:/127.0.0.1:8080] ACTIVE
000000____
111_______
2222222222
333333____
444_______
55________
6666666___
77777_____
8888______
99999_____
13:51:29 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xdc9dffac, L:/127.0.0.1:50973 - R:/127.0.0.1:8080] WRITE: 100B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 30 30 30 30 5f 5f 5f 5f 31 31 31 5f 5f 5f |000000____111___|
|00000010| 5f 5f 5f 5f 32 32 32 32 32 32 32 32 32 32 33 33 |____222222222233|
|00000020| 33 33 33 33 5f 5f 5f 5f 34 34 34 5f 5f 5f 5f 5f |3333____444_____|
|00000030| 5f 5f 35 35 5f 5f 5f 5f 5f 5f 5f 5f 36 36 36 36 |__55________6666|
|00000040| 36 36 36 5f 5f 5f 37 37 37 37 37 5f 5f 5f 5f 5f |666___77777_____|
|00000050| 38 38 38 38 5f 5f 5f 5f 5f 5f 39 39 39 39 39 5f |8888______99999_|
|00000060| 5f 5f 5f 5f                                     |____            |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xdc9dffac, L:/127.0.0.1:50973 - R:/127.0.0.1:8080] FLUSH

服务端输出，重点看服务端输出，服务端每10个字节接收作为一条消息，交给后面的handler处理，并没有发生半包

13:51:21 [DEBUG] [main] c.z.a.HelloWorldServer - [id: 0xafdaf078] binding...
13:51:21 [DEBUG] [main] c.z.a.HelloWorldServer - [id: 0xafdaf078, L:/0:0:0:0:0:0:0:0:8080] bound...
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] REGISTERED
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] ACTIVE
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 30 30 30 30 5f 5f 5f 5f                   |000000____      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 31 31 31 5f 5f 5f 5f 5f 5f 5f                   |111_______      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 32 32 32 32 32 32 32 32 32 32                   |2222222222      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 33 33 33 33 33 33 5f 5f 5f 5f                   |333333____      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 34 34 34 5f 5f 5f 5f 5f 5f 5f                   |444_______      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 35 35 5f 5f 5f 5f 5f 5f 5f 5f                   |55________      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 36 36 36 36 36 36 36 5f 5f 5f                   |6666666___      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 37 37 37 37 37 5f 5f 5f 5f 5f                   |77777_____      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 38 38 38 38 5f 5f 5f 5f 5f 5f                   |8888______      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ: 10B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 39 39 39 39 39 5f 5f 5f 5f 5f                   |99999_____      |
+--------+-------------------------------------------------+----------------+
13:51:29 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x0d23d3d4, L:/127.0.0.1:8080 - R:/127.0.0.1:50973] READ COMPLETE

缺点是，数据包的大小不好把握

• 长度定的太大，浪费
• 长度定的太小，对某些数据包又显得不够

方法3，固定分隔符

服务端代码

• 服务端加入，默认以 \n 或 \r\n 作为分隔符的处理器（如果超出最大长度仍未出现分隔符，则抛出异常）

@Slf4j
public class HelloWorldServer {void start() {NioEventLoopGroup boss = new NioEventLoopGroup(1);NioEventLoopGroup worker = new NioEventLoopGroup();try {ServerBootstrap serverBootstrap = new ServerBootstrap();// 为现象明显，服务端修改一下接收缓冲区，其它代码不变// (调整系统的接收缓冲区（即滑动窗口）)// serverBootstrap.option(ChannelOption.SO_RCVBUF, 10);// 调整netty的接收缓冲区// serverBootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR,//                             new AdaptiveRecvByteBufAllocator(16, 16, 16));serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.group(boss, worker);serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {// 注意顺序: 要先添加基于分隔符的解码处理器, 再添加日志处理器ch.pipeline().addLast(new LineBasedFrameDecoder(1024));ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));}});ChannelFuture channelFuture = serverBootstrap.bind(8080);log.debug("{} binding...", channelFuture.channel());channelFuture.sync();log.debug("{} bound...", channelFuture.channel());channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("server error", e);} finally {boss.shutdownGracefully();worker.shutdownGracefully();log.debug("stoped");}}public static void main(String[] args) {new HelloWorldServer().start();}
}

客户端代码

客户端在每条消息之后，加入 \n 分隔符

@Slf4j
public class HelloWorldClient {public static void main(String[] args) {send();}private static void send() {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {// 会在连接 channel 建立成功之后，会触发 active事件@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {/*在每条消息后面加上1个\n, 来表示消息的分隔符*/ByteBuf buf = ctx.alloc().buffer();char c = '0';Random r = new Random();for (int i = 0; i < 10; i++) {StringBuilder sb = makeString(c, r.nextInt(256) + 1);buf.writeBytes(sb.toString().getBytes());c++;}// 还是1次性写入bufctx.writeAndFlush(buf);}});}});ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}public static StringBuilder makeString(char c, int len) {StringBuilder sb = new StringBuilder(len + 2);for (int i = 0; i < len; i++) {sb.append(c);}sb.append("\n");return sb;}
}

客户端输出

14:27:28 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x45f4846a] REGISTERED
14:27:28 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x45f4846a] CONNECT: /127.0.0.1:8080
14:27:28 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x45f4846a, L:/127.0.0.1:54341 - R:/127.0.0.1:8080] ACTIVE
14:27:28 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x45f4846a, L:/127.0.0.1:54341 - R:/127.0.0.1:8080] WRITE: 1445B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000010| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000020| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000030| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000040| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000050| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000060| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000070| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000080| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000090| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000a0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000b0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000c0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000d0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000e0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000f0| 30 30 30 30 0a 31 31 31 31 31 31 31 31 31 31 31 |0000.11111111111|
|00000100| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000110| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000120| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000130| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000140| 31 31 31 31 31 31 31 31 31 31 31 31 31 0a 32 32 |1111111111111.22|
|00000150| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000160| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000170| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000180| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000190| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000001a0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000001b0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000001c0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000001d0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000001e0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000001f0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000200| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000210| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000220| 32 32 0a 33 33 33 33 33 33 33 33 33 33 33 33 33 |22.3333333333333|
|00000230| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000240| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000250| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000260| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000270| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000280| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000290| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000002a0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000002b0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000002c0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000002d0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000002e0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000002f0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000300| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000310| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000320| 0a 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |.444444444444444|
|00000330| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000340| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000350| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000360| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000370| 34 34 0a 35 35 35 35 35 35 35 35 35 35 35 35 35 |44.5555555555555|
|00000380| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|00000390| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|000003a0| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|000003b0| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|000003c0| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|000003d0| 35 35 35 35 35 35 35 0a 36 36 36 36 36 36 36 36 |5555555.66666666|
|000003e0| 36 36 36 36 36 36 0a 37 37 37 37 37 37 37 37 37 |666666.777777777|
|000003f0| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000400| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000410| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000420| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000430| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000440| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000450| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000460| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000470| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000480| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000490| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000004a0| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000004b0| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000004c0| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000004d0| 37 0a 38 38 38 38 38 38 38 38 38 38 38 38 38 38 |7.88888888888888|
|000004e0| 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 |8888888888888888|
|000004f0| 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 |8888888888888888|
|00000500| 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 |8888888888888888|
|00000510| 38 38 38 38 38 38 38 0a 39 39 39 39 39 39 39 39 |8888888.99999999|
|00000520| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000530| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000540| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000550| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000560| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000570| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000580| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000590| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|000005a0| 39 39 39 39 0a                                  |9999.           |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x45f4846a, L:/127.0.0.1:54341 - R:/127.0.0.1:8080] FLUSH

服务端输出

14:27:25 [DEBUG] [main] c.z.a.HelloWorldServer - [id: 0xd4acc436] binding...
14:27:25 [DEBUG] [main] c.z.a.HelloWorldServer - [id: 0xd4acc436, L:/0:0:0:0:0:0:0:0:8080] bound...
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] REGISTERED
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] ACTIVE
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 244B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000010| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000020| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000030| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000040| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000050| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000060| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000070| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000080| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|00000090| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000a0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000b0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000c0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000d0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000e0| 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 30 |0000000000000000|
|000000f0| 30 30 30 30                                     |0000            |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 88B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000010| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000020| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000030| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000040| 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 31 |1111111111111111|
|00000050| 31 31 31 31 31 31 31 31                         |11111111        |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 212B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000010| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000020| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000030| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000040| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000050| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000060| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000070| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000080| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|00000090| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000000a0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000000b0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000000c0| 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 32 |2222222222222222|
|000000d0| 32 32 32 32                                     |2222            |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 253B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000010| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000020| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000030| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000040| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000050| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000060| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000070| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000080| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|00000090| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000000a0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000000b0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000000c0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000000d0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000000e0| 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 33 |3333333333333333|
|000000f0| 33 33 33 33 33 33 33 33 33 33 33 33 33          |3333333333333   |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 81B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000010| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000020| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000030| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000040| 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 |4444444444444444|
|00000050| 34                                              |4               |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 100B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|00000010| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|00000020| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|00000030| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|00000040| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|00000050| 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 35 |5555555555555555|
|00000060| 35 35 35 35                                     |5555            |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 14B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 36 36 36 36 36 36 36 36 36 36 36 36 36 36       |66666666666666  |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 234B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000010| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000020| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000030| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000040| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000050| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000060| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000070| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000080| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|00000090| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000000a0| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000000b0| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000000c0| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000000d0| 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 37 |7777777777777777|
|000000e0| 37 37 37 37 37 37 37 37 37 37                   |7777777777      |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 69B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 |8888888888888888|
|00000010| 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 |8888888888888888|
|00000020| 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 |8888888888888888|
|00000030| 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 38 |8888888888888888|
|00000040| 38 38 38 38 38                                  |88888           |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ: 140B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000010| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000020| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000030| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000040| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000050| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000060| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000070| 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 39 |9999999999999999|
|00000080| 39 39 39 39 39 39 39 39 39 39 39 39             |999999999999    |
+--------+-------------------------------------------------+----------------+
14:27:28 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x8dfc81f2, L:/127.0.0.1:8080 - R:/127.0.0.1:54341] READ COMPLETE

缺点，处理字符数据比较合适，但如果内容本身包含了分隔符（字节数据常常会有此情况），那么就会解析错误

方法4，预设长度

在发送消息前，先约定用定长字节表示接下来数据的长度

LengthFieldBasedFrameDecoder

• lengthFieldOffset - 长度字段偏移量

• lengthFieldLength - 长度字段长度

• lengthAdjustment - 长度字段为基准，还要跳过几个字节才是内容

• initialBytesTostrip - 从头剥离几个字节

// 最大长度，长度偏移，长度占用字节，长度调整，剥离字节数
ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(1024, 0, 1, 0, 1));

测试示例，使用EmbeddedChannel模拟

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import io.netty.channel.embedded.EmbeddedChannel;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;public class TestLengthFieldDecoder {public static void main(String[] args) {// 注意处理器的添加顺序EmbeddedChannel channel = new EmbeddedChannel(new LengthFieldBasedFrameDecoder(1024, 0, 4, 1, 5),new LoggingHandler(LogLevel.DEBUG));//  4 个字节的内容长度， 实际内容ByteBuf buffer = ByteBufAllocator.DEFAULT.buffer();// 模拟对方发送过来消息send(buffer, "Hello, world");send(buffer, "Hi!");// 把消息写入channelchannel.writeInbound(buffer);}private static void send(ByteBuf buffer, String content) {// 实际内容byte[] bytes = content.getBytes();// 实际内容长度int length = bytes.length;// 写入内容长度buffer.writeInt(length);// 写入版本号buffer.writeByte(1);// 写入实际内容buffer.writeBytes(bytes);}
}
// 输出
/*
16:09:07 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] REGISTERED
16:09:07 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] ACTIVE
16:09:07 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 12B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 65 6c 6c 6f 2c 20 77 6f 72 6c 64             |Hello, world    |
+--------+-------------------------------------------------+----------------+
16:09:07 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 3B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 69 21                                        |Hi!             |
+--------+-------------------------------------------------+----------------+
16:09:07 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE
*/

2. 协议设计与解析

2.1 为什么需要协议？

TCP/IP 中消息传输基于流的方式，没有边界。

协议的目的就是划定消息的边界，制定通信双方要共同遵守的通信规则

例如：在网络上传输

下雨天留客天留我不留

是中文一句著名的无标点符号句子，在没有标点符号情况下，这句话有数种拆解方式，而意思却是完全不同，所以常被用作讲述标点符号的重要性

一种解读

下雨天留客，天留，我不留

另一种解读

下雨天，留客天，留我不？留

如何设计协议呢？其实就是给网络传输的信息加上“标点符号”。但通过分隔符来断句不是很好，因为分隔符本身如果用于传输，那么必须加以区分。因此，下面一种协议较为常用

定长字节表示内容长度 + 实际内容

例如，假设一个中文字符长度为 3，按照上述协议的规则，发送信息方式如下，就不会被接收方弄错意思了

0f下雨天留客06天留09我不留

小故事

很久很久以前，一位私塾先生到一家任教。双方签订了一纸协议：“无鸡鸭亦可无鱼肉亦可白菜豆腐不可少不得束修金”。此后，私塾先生虽然认真教课，但主人家则总是给私塾先生以白菜豆腐为菜，丝毫未见鸡鸭鱼肉的款待。私塾先生先是很不解，可是后来也就想通了：主人把鸡鸭鱼肉的钱都会换为束修金的，也罢。至此双方相安无事。

年关将至，一个学年段亦告结束。私塾先生临行时，也不见主人家为他交付束修金，遂与主家理论。然主家亦振振有词：“有协议为证——无鸡鸭亦可，无鱼肉亦可，白菜豆腐不可少，不得束修金。这白纸黑字明摆着的，你有什么要说的呢？”

私塾先生据理力争：“协议是这样的——无鸡，鸭亦可；无鱼，肉亦可；白菜豆腐不可，少不得束修金。”

双方唇枪舌战，你来我往，真个是不亦乐乎！

这里的束修金，也作“束脩”，应当是泛指教师应当得到的报酬

2.2 redis 协议举例

使用netty编写客户端，连接redis，并且发送set aaa bbb，get aaa 这2个命令

@Slf4j
public class TestRedis {/*set name zhangsan*3  （3个元素 \r\n）$3  （第一个元素3个字节 \r\n）set （set 3个字节）$4  （第二个元素4个字节 \r\n）name（name 4个字节）$8  （第三个元素8个字节 \r\n）zhangsan（zhangsan 8个字节）*/public static void main(String[] args) {NioEventLoopGroup worker = new NioEventLoopGroup();byte[] LINE = new byte[]{13, 10};System.out.println(LINE_BYTES[0] == '\r');System.out.println(LINE_BYTES[1] == '\n');try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) {ch.pipeline().addLast(new LoggingHandler());ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {// 会在连接 channel 建立成功后，会触发 active 事件@Overridepublic void channelActive(ChannelHandlerContext ctx) {// 执行命令: set aaa bbbset(ctx);// 执行命令: get aaaget(ctx);}private void get(ChannelHandlerContext ctx) {ByteBuf buf = ctx.alloc().buffer();buf.writeBytes("*2".getBytes());buf.writeBytes(LINE);buf.writeBytes("$3".getBytes());buf.writeBytes(LINE);buf.writeBytes("get".getBytes());buf.writeBytes(LINE);buf.writeBytes("$3".getBytes());buf.writeBytes(LINE);buf.writeBytes("aaa".getBytes());buf.writeBytes(LINE);ctx.writeAndFlush(buf);}private void set(ChannelHandlerContext ctx) {ByteBuf buf = ctx.alloc().buffer();buf.writeBytes("*3".getBytes());buf.writeBytes(LINE);buf.writeBytes("$3".getBytes());buf.writeBytes(LINE);buf.writeBytes("set".getBytes());buf.writeBytes(LINE);buf.writeBytes("$3".getBytes());buf.writeBytes(LINE);buf.writeBytes("aaa".getBytes());buf.writeBytes(LINE);buf.writeBytes("$3".getBytes());buf.writeBytes(LINE);buf.writeBytes("bbb".getBytes());buf.writeBytes(LINE); // 注意：最后面的这个\r\n也不能省略ctx.writeAndFlush(buf); }@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {ByteBuf buf = (ByteBuf) msg;System.out.println(buf.toString(Charset.defaultCharset()));// 我觉得这里应该需要释放buf吧??}});}});ChannelFuture channelFuture = bootstrap.connect("localhost", 6379).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully(); // 优雅关闭}}
}
// 输出日志
/*12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1] REGISTERED
12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1] CONNECT: localhost/127.0.0.1:6379
12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1, L:/127.0.0.1:58542 - R:localhost/127.0.0.1:6379] ACTIVE
12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1, L:/127.0.0.1:58542 - R:localhost/127.0.0.1:6379] WRITE: 31B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 2a 33 0d 0a 24 33 0d 0a 73 65 74 0d 0a 24 33 0d |*3..$3..set..$3.|
|00000010| 0a 61 61 61 0d 0a 24 33 0d 0a 62 62 62 0d 0a    |.aaa..$3..bbb.. |
+--------+-------------------------------------------------+----------------+
12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1, L:/127.0.0.1:58542 - R:localhost/127.0.0.1:6379] FLUSH
12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1, L:/127.0.0.1:58542 - R:localhost/127.0.0.1:6379] WRITE: 22B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 2a 32 0d 0a 24 33 0d 0a 67 65 74 0d 0a 24 33 0d |*2..$3..get..$3.|
|00000010| 0a 61 61 61 0d 0a                               |.aaa..          |
+--------+-------------------------------------------------+----------------+
12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1, L:/127.0.0.1:58542 - R:localhost/127.0.0.1:6379] FLUSH
12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1, L:/127.0.0.1:58542 - R:localhost/127.0.0.1:6379] READ: 14B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 2b 4f 4b 0d 0a 24 33 0d 0a 62 62 62 0d 0a       |+OK..$3..bbb..  |
+--------+-------------------------------------------------+----------------+
+OK
$3
bbb12:57:21 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x80c5b3b1, L:/127.0.0.1:58542 - R:localhost/127.0.0.1:6379] READ COMPLETE*/

2.3 http 协议举例

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.http.*;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import lombok.extern.slf4j.Slf4j;@Slf4j
public class TestHttp {public static void main(String[] args) throws InterruptedException {NioEventLoopGroup boss = new NioEventLoopGroup(1);NioEventLoopGroup worker = new NioEventLoopGroup();try {ServerBootstrap serverBootstrap = new ServerBootstrap().group(boss, worker).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));// 配置http编解码器（包括编码、解码）// 解码 - 把发向服务端的请求ByteBuf解码// 编码 - 把发给客户端的数据编码成ByteBuf, 以便写出字节数据// （HttpServerCodec继承自CombinedChannelDuplexHandler<HttpRequestDecoder,//                                                   HttpResponseEncoder>）ch.pipeline().addLast(new HttpServerCodec());// 注意写入的泛型, 表示该处理器只处理该类型的消息ch.pipeline().addLast(new SimpleChannelInboundHandler<HttpRequest>() {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, HttpRequest msg) throws Exception {// 获取请求urilog.info(msg.uri());// 响应对象DefaultFullHttpResponse response = new DefaultFullHttpResponse(msg.protocolVersion(), HttpResponseStatus.OK);byte[] content = "<h1>hello,world</h1>".getBytes();response.content().writeBytes(content);// 告诉浏览器, 响应内容就这么长, 不然浏览器会一直傻傻的等待接收后面的内容// （网站图标位置一直在转圈圈）response.headers().set(HttpHeaderNames.CONTENT_LENGTH, content.length);// 写回响应// （这个response将会经过HttpServerCodec出站处理器，将它编码了，//   再返回回去）ctx.writeAndFlush(response);}});/*// 当浏览器发起1个get请求后, 该处理器的channelRead方法被调用了2次，//      - 第一次传过来的msg是 DefaultHttpRequest(decodeResult: success,version: HTTP/1.1)//      - 第二次传过来的是 EmptyLastHttpContentch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {log.info("接收到请求: {}", msg);// HttpServerCodec会把接收到的请求, // 分为 HttpRequest 和 HttpContent(对该handler进行了2次调用)// 如果只处理其中某一种类型的消息，可以如上使用// SimpleChannelInboundHandler，// 并指定泛型（比如上面就指定了HttpRequest）if (msg instanceof HttpRequest) { // 请求行 和 请求头log.info("HttpRequest msg: {}", msg);} else if (msg instanceof HttpContent) { // 请求体log.info("HttpContent msg: {}", msg);}}});*/}});ChannelFuture channelFuture = serverBootstrap.bind(8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {e.printStackTrace();} finally {boss.shutdownGracefully();worker.shutdownGracefully();}}
}

2.4 自定义协议要素

• 魔数，用来在第一时间判定是否是无效数据包
• 版本号，可以支持协议的升级
• 序列化算法，消息正文到底采用哪种序列化反序列化方式，可以由此扩展，例如：json、protobuf、hessian、jdk
• 指令类型，是登录、注册、单聊、群聊… 跟业务相关
• 请求序号，为了双工通信，提供异步能力
• 正文长度
• 消息正文

编解码器

根据上面的要素，设计一个登录请求消息和登录响应消息，并使用 Netty 完成收发

MessageCodec

@Slf4j
public class MessageCodec extends ByteToMessageCodec<Message> {@Overridepublic void encode(ChannelHandlerContext ctx, Message msg, ByteBuf out) throws Exception {// 1. 4 字节的魔数out.writeBytes(new byte[]{1, 2, 3, 4});// 2. 1 字节的版本,out.writeByte(1);// 3. 1 字节的序列化方式 jdk 0 , json 1out.writeByte(0);// 4. 1 字节的指令类型out.writeByte(msg.getMessageType());// 5. 4 个字节out.writeInt(msg.getSequenceId());// 无意义，对齐填充，为了满2^n固定字节数, 正好凑够16个固定字节数out.writeByte(0xff);/* 将Message对象先转为字节数组(使用ByteArrayOutputStream + ObjectOutputStream),然后把字节数组写到ByteBuf中 */// 6. 获取内容的字节数组ByteArrayOutputStream bos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(bos);oos.writeObject(msg);byte[] bytes = bos.toByteArray();// 7. 长度out.writeInt(bytes.length);// 8. 写入内容out.writeBytes(bytes);log.info("message 编码完成...{}", msg);}@Overrideprotected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {// 读取 4 字节的魔数（读指针向后移动4位）int magicNum = in.readInt();// 读取 1 字节的版本byte version = in.readByte();// 读取 1 字节的序列化方式byte serializerType = in.readByte();// 读取 1 字节的指令类型byte messageType = in.readByte();// 读取 4 个字节 序列idint sequenceId = in.readInt();// 读取 无意义 的字节（将读指针向后移动1位）in.readByte();// 读取 长度int length = in.readInt();// 使用读取到的长度创建字节数组byte[] bytes = new byte[length];// 将ByteBuf读取到字节数组in.readBytes(bytes, 0, length);/* 这里将ByteBuf的数据, 通过jdk反序列化的方式, 转为java对象,那就要保证这个数据一定是对象完整的序列化字节数据,如果不是一个完整的数据（即出现半包的情况）, 那就废了。因此，*/// jdk反序列化 将字节数组 转为 Message对象ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bytes));Message message = (Message) ois.readObject();log.debug("{}, {}, {}, {}, {}, {}", magicNum, version, serializerType, messageType, sequenceId, length);log.debug("message 解码完成{}", message);// 将消息添加到out集合当中out.add(message);}
}

TestMessageCodec

@Slf4j
public class TestMessageCodec {public static void main(String[] args) throws Exception {EmbeddedChannel channel = new EmbeddedChannel(new LoggingHandler(),// 参数的含义：数据的最大长度为1024个字节、从索引0开始,偏移12个字节开始,是实际内容长度信息、//           实际内容长度占4个字节、不做调整(即不偏移,实际内容长度后面开始就是实际内容)、//           不剥离前面的字节（因为在MessageCodec中有解析前面的字节）// 帧解码器，解决粘包&半包问题// （如果发现数据不完整(即发生了半包问题), 它是不会把消息传递给下一个处理器处理的,//   等数据完整了，它才会把完整的消息发给下一个处理器）// 此处可用来解决半包的问题: 也就是说, 实际内容长度可能有239个字节, 但是本次只收到了100个字节,//                       那如果往后面读的话, 就读不满239个字节, 那就等接收到下一次消息后,//                       一直到满了239个字节, 再把这个完整的消息, 传递给下一个handlernew LengthFieldBasedFrameDecoder(1024, 12, 4, 0, 0),// 自定义编解码器new MessageCodec());log.info("------------------测试编码-----------------");// 测试encodeLoginRequestMessage message = new LoginRequestMessage("zhangsan", "123");// 向channel中写出数据（MessageCodec会对message作编码处理，写入到ByteBuf）channel.writeOutbound(message);log.info("------------------测试解码-----------------");// 测试decode// 先使用MessageCodec将message写入到ByteBufByteBuf buf = ByteBufAllocator.DEFAULT.buffer();new MessageCodec().encode(null, message, buf);// 将buf切片成2部分, 模拟半包(先接收100字节, 然后再接收剩下的字节),// 注意: 须使用LengthFieldBasedFrameDecoder处理半包问题ByteBuf s1 = buf.slice(0, 100);ByteBuf s2 = buf.slice(100, buf.readableBytes() - 100);s1.retain(); // 引用计数+1（即现在为2）// 这个方法默认会释放buf（release 1）,接收半包后的数据时,buf被释放了就会报错(下面这句会报错)// 因此上面就使用了s1.retain()让引用计数+1了channel.writeInbound(s1);channel.writeInbound(s2);}
}

输出

观察下面的输出

1. 编码的时候, 写出了224个字节
2. 解码的时候，接受了2次，第一次接受收了100个字节，第二次接收了124个字节，并且只出现了1次解码完成，这说明在出现了半包的情况下LengthFieldBasedFrameDecoder帮助我们解决了半包问题，并且它会接收一个完整的包后，才会传给后面的handler
3. 可以留意一下，在写出的时候，第一行的字节数据 正好 符合 我们的编码规则哦

21:50:22 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] REGISTERED
21:50:22 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] ACTIVE
21:50:22 [INFO ] [main] c.i.a.c.TestMessageCodec - ------------------测试编码-----------------
21:50:22 [INFO ] [main] c.i.p.MessageCodec - message 编码完成...LoginRequestMessage(super=Message(sequenceId=0, messageType=0), username=zhangsan, password=123)
21:50:22 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] WRITE: 214B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 01 02 03 04 01 00 00 00 00 00 00 ff 00 00 00 c6 |................|
|00000010| ac ed 00 05 73 72 00 25 63 6e 2e 69 74 63 61 73 |....sr.%cn.itcas|
|00000020| 74 2e 6d 65 73 73 61 67 65 2e 4c 6f 67 69 6e 52 |t.message.LoginR|
|00000030| 65 71 75 65 73 74 4d 65 73 73 61 67 65 a0 3f 71 |equestMessage.?q|
|00000040| cb 31 45 b5 88 02 00 02 4c 00 08 70 61 73 73 77 |.1E.....L..passw|
|00000050| 6f 72 64 74 00 12 4c 6a 61 76 61 2f 6c 61 6e 67 |ordt..Ljava/lang|
|00000060| 2f 53 74 72 69 6e 67 3b 4c 00 08 75 73 65 72 6e |/String;L..usern|
|00000070| 61 6d 65 71 00 7e 00 01 78 72 00 19 63 6e 2e 69 |ameq.~..xr..cn.i|
|00000080| 74 63 61 73 74 2e 6d 65 73 73 61 67 65 2e 4d 65 |tcast.message.Me|
|00000090| 73 73 61 67 65 3d dd 19 a0 bc 07 47 cb 02 00 02 |ssage=.....G....|
|000000a0| 49 00 0b 6d 65 73 73 61 67 65 54 79 70 65 49 00 |I..messageTypeI.|
|000000b0| 0a 73 65 71 75 65 6e 63 65 49 64 78 70 00 00 00 |.sequenceIdxp...|
|000000c0| 00 00 00 00 00 74 00 03 31 32 33 74 00 08 7a 68 |.....t..123t..zh|
|000000d0| 61 6e 67 73 61 6e                               |angsan          |
+--------+-------------------------------------------------+----------------+
21:50:22 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] FLUSH
21:50:22 [INFO ] [main] c.i.a.c.TestMessageCodec - ------------------测试解码-----------------
21:50:22 [INFO ] [main] c.i.p.MessageCodec - message 编码完成...LoginRequestMessage(super=Message(sequenceId=0, messageType=0), username=zhangsan, password=123)
21:50:22 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 100B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 01 02 03 04 01 00 00 00 00 00 00 ff 00 00 00 c6 |................|
|00000010| ac ed 00 05 73 72 00 25 63 6e 2e 69 74 63 61 73 |....sr.%cn.itcas|
|00000020| 74 2e 6d 65 73 73 61 67 65 2e 4c 6f 67 69 6e 52 |t.message.LoginR|
|00000030| 65 71 75 65 73 74 4d 65 73 73 61 67 65 a0 3f 71 |equestMessage.?q|
|00000040| cb 31 45 b5 88 02 00 02 4c 00 08 70 61 73 73 77 |.1E.....L..passw|
|00000050| 6f 72 64 74 00 12 4c 6a 61 76 61 2f 6c 61 6e 67 |ordt..Ljava/lang|
|00000060| 2f 53 74 72                                     |/Str            |
+--------+-------------------------------------------------+----------------+
21:50:22 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE
21:50:22 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 114B+-------------------------------------------------+|  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 6e 67 3b 4c 00 08 75 73 65 72 6e 61 6d 65 71 |ing;L..usernameq|
|00000010| 00 7e 00 01 78 72 00 19 63 6e 2e 69 74 63 61 73 |.~..xr..cn.itcas|
|00000020| 74 2e 6d 65 73 73 61 67 65 2e 4d 65 73 73 61 67 |t.message.Messag|
|00000030| 65 3d dd 19 a0 bc 07 47 cb 02 00 02 49 00 0b 6d |e=.....G....I..m|
|00000040| 65 73 73 61 67 65 54 79 70 65 49 00 0a 73 65 71 |essageTypeI..seq|
|00000050| 75 65 6e 63 65 49 64 78 70 00 00 00 00 00 00 00 |uenceIdxp.......|
|00000060| 00 74 00 03 31 32 33 74 00 08 7a 68 61 6e 67 73 |.t..123t..zhangs|
|00000070| 61 6e                                           |an              |
+--------+-------------------------------------------------+----------------+
21:50:22 [DEBUG] [main] c.i.p.MessageCodec - 16909060, 1, 0, 0, 0, 198
21:50:22 [DEBUG] [main] c.i.p.MessageCodec - message 解码完成LoginRequestMessage(super=Message(sequenceId=0, messageType=0), username=zhangsan, password=123)
21:50:22 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETE

💡 什么时候可以加 @Sharable

• 当 handler 不保存状态时，就可以安全地在多线程下被共享
• 但要注意对于编解码器类，不能继承 ByteToMessageCodec 或 CombinedChannelDuplexHandler 父类，他们的构造方法对 @Sharable 有限制
• 如果能确保编解码器不会保存状态，可以继承 MessageToMessageCodec 父类

@Slf4j
@ChannelHandler.Sharable
/*** 必须和 LengthFieldBasedFrameDecoder 一起使用，确保接到的 ByteBuf 消息是完整的*/
public class MessageCodecSharable extends MessageToMessageCodec<ByteBuf, Message> {@Overrideprotected void encode(ChannelHandlerContext ctx, Message msg, List<Object> outList) throws Exception {ByteBuf out = ctx.alloc().buffer();// 1. 4 字节的魔数out.writeBytes(new byte[]{1, 2, 3, 4});// 2. 1 字节的版本,out.writeByte(1);// 3. 1 字节的序列化方式 jdk 0 , json 1out.writeByte(0);// 4. 1 字节的指令类型out.writeByte(msg.getMessageType());// 5. 4 个字节out.writeInt(msg.getSequenceId());// 无意义，对齐填充out.writeByte(0xff);// 6. 获取内容的字节数组ByteArrayOutputStream bos = new ByteArrayOutputStream();ObjectOutputStream oos = new ObjectOutputStream(bos);oos.writeObject(msg);byte[] bytes = bos.toByteArray();// 7. 长度out.writeInt(bytes.length);// 8. 写入内容out.writeBytes(bytes);outList.add(out);}@Overrideprotected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {int magicNum = in.readInt();byte version = in.readByte();byte serializerType = in.readByte();byte messageType = in.readByte();int sequenceId = in.readInt();in.readByte();int length = in.readInt();byte[] bytes = new byte[length];in.readBytes(bytes, 0, length);ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(bytes));Message message = (Message) ois.readObject();log.debug("{}, {}, {}, {}, {}, {}", magicNum, version, serializerType, messageType, sequenceId, length);log.debug("{}", message);out.add(message);}
}

3. 聊天室案例

3.1 聊天室业务介绍

/*** 用户管理接口*/
public interface UserService {/*** 登录* @param username 用户名* @param password 密码* @return 登录成功返回 true, 否则返回 false*/boolean login(String username, String password);
}

/*** 会话管理接口*/
public interface Session {/*** 绑定会话* @param channel 哪个 channel 要绑定会话* @param username 会话绑定用户*/void bind(Channel channel, String username);/*** 解绑会话* @param channel 哪个 channel 要解绑会话*/void unbind(Channel channel);/*** 获取属性* @param channel 哪个 channel* @param name 属性名* @return 属性值*/Object getAttribute(Channel channel, String name);/*** 设置属性* @param channel 哪个 channel* @param name 属性名* @param value 属性值*/void setAttribute(Channel channel, String name, Object value);/*** 根据用户名获取 channel* @param username 用户名* @return channel*/Channel getChannel(String username);
}

/*** 聊天组会话管理接口*/
public interface GroupSession {/*** 创建一个聊天组, 如果不存在才能创建成功, 否则返回 null* @param name 组名* @param members 成员* @return 成功时返回组对象, 失败返回 null*/Group createGroup(String name, Set<String> members);/*** 加入聊天组* @param name 组名* @param member 成员名* @return 如果组不存在返回 null, 否则返回组对象*/Group joinMember(String name, String member);/*** 移除组成员* @param name 组名* @param member 成员名* @return 如果组不存在返回 null, 否则返回组对象*/Group removeMember(String name, String member);/*** 移除聊天组* @param name 组名* @return 如果组不存在返回 null, 否则返回组对象*/Group removeGroup(String name);/*** 获取组成员* @param name 组名* @return 成员集合, 没有成员会返回 empty set*/Set<String> getMembers(String name);/*** 获取组成员的 channel 集合, 只有在线的 channel 才会返回* @param name 组名* @return 成员 channel 集合*/List<Channel> getMembersChannel(String name);
}

3.2 聊天室业务-登录

@Slf4j
public class ChatServer {public static void main(String[] args) {NioEventLoopGroup boss = new NioEventLoopGroup();NioEventLoopGroup worker = new NioEventLoopGroup();LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG);MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable();try {ServerBootstrap serverBootstrap = new ServerBootstrap();serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.group(boss, worker);serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new ProcotolFrameDecoder());ch.pipeline().addLast(LOGGING_HANDLER);ch.pipeline().addLast(MESSAGE_CODEC);ch.pipeline().addLast(new SimpleChannelInboundHandler<LoginRequestMessage>() {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, LoginRequestMessage msg) throws Exception {String username = msg.getUsername();String password = msg.getPassword();boolean login = UserServiceFactory.getUserService().login(username, password);LoginResponseMessage message;if(login) {message = new LoginResponseMessage(true, "登录成功");} else {message = new LoginResponseMessage(false, "用户名或密码不正确");}ctx.writeAndFlush(message);}});}});Channel channel = serverBootstrap.bind(8080).sync().channel();channel.closeFuture().sync();} catch (InterruptedException e) {log.error("server error", e);} finally {boss.shutdownGracefully();worker.shutdownGracefully();}}
}

@Slf4j
public class ChatClient {public static void main(String[] args) {NioEventLoopGroup group = new NioEventLoopGroup();LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG);MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable();CountDownLatch WAIT_FOR_LOGIN = new CountDownLatch(1);AtomicBoolean LOGIN = new AtomicBoolean(false);try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(group);bootstrap.handler(new ChannelInitializer<SocketChannel>() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new ProcotolFrameDecoder());
//                    ch.pipeline().addLast(LOGGING_HANDLER);ch.pipeline().addLast(MESSAGE_CODEC);ch.pipeline().addLast("client handler", new ChannelInboundHandlerAdapter() {// 接收响应消息@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {log.debug("msg: {}", msg);if ((msg instanceof LoginResponseMessage)) {LoginResponseMessage response = (LoginResponseMessage) msg;if (response.isSuccess()) {// 如果登录成功LOGIN.set(true);}// 唤醒 system in 线程WAIT_FOR_LOGIN.countDown();}}// 在连接建立后触发 active 事件@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {// 负责接收用户在控制台的输入，负责向服务器发送各种消息new Thread(() -> {Scanner scanner = new Scanner(System.in);System.out.println("请输入用户名:");String username = scanner.nextLine();System.out.println("请输入密码:");String password = scanner.nextLine();// 构造消息对象LoginRequestMessage message = new LoginRequestMessage(username, password);// 发送消息ctx.writeAndFlush(message);System.out.println("等待后续操作...");try {WAIT_FOR_LOGIN.await();} catch (InterruptedException e) {e.printStackTrace();}// 如果登录失败if (!LOGIN.get()) {ctx.channel().close();return;}while (true) {System.out.println("==================================");System.out.println("send [username] [content]");System.out.println("gsend [group name] [content]");System.out.println("gcreate [group name] [m1,m2,m3...]");System.out.println("gmembers [group name]");System.out.println("gjoin [group name]");System.out.println("gquit [group name]");System.out.println("quit");System.out.println("==================================");String command = scanner.nextLine();String[] s = command.split(" ");switch (s[0]){case "send":ctx.writeAndFlush(new ChatRequestMessage(username, s[1], s[2]));break;case "gsend":ctx.writeAndFlush(new GroupChatRequestMessage(username, s[1], s[2]));break;case "gcreate":Set<String> set = new HashSet<>(Arrays.asList(s[2].split(",")));set.add(username); // 加入自己ctx.writeAndFlush(new GroupCreateRequestMessage(s[1], set));break;case "gmembers":ctx.writeAndFlush(new GroupMembersRequestMessage(s[1]));break;case "gjoin":ctx.writeAndFlush(new GroupJoinRequestMessage(username, s[1]));break;case "gquit":ctx.writeAndFlush(new GroupQuitRequestMessage(username, s[1]));break;case "quit":ctx.channel().close();return;}}}, "system in").start();}});}});Channel channel = bootstrap.connect("localhost", 8080).sync().channel();channel.closeFuture().sync();} catch (Exception e) {log.error("client error", e);} finally {group.shutdownGracefully();}}
}

3.3 聊天室业务-单聊

服务器端将 handler 独立出来

登录 handler

@ChannelHandler.Sharable
public class LoginRequestMessageHandler extends SimpleChannelInboundHandler<LoginRequestMessage> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, LoginRequestMessage msg) throws Exception {String username = msg.getUsername();String password = msg.getPassword();boolean login = UserServiceFactory.getUserService().login(username, password);LoginResponseMessage message;if(login) {SessionFactory.getSession().bind(ctx.channel(), username);message = new LoginResponseMessage(true, "登录成功");} else {message = new LoginResponseMessage(false, "用户名或密码不正确");}ctx.writeAndFlush(message);}
}

单聊 handler

@ChannelHandler.Sharable
public class ChatRequestMessageHandler extends SimpleChannelInboundHandler<ChatRequestMessage> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, ChatRequestMessage msg) throws Exception {String to = msg.getTo();Channel channel = SessionFactory.getSession().getChannel(to);// 在线if(channel != null) {channel.writeAndFlush(new ChatResponseMessage(msg.getFrom(), msg.getContent()));}// 不在线else {ctx.writeAndFlush(new ChatResponseMessage(false, "对方用户不存在或者不在线"));}}
}

3.4 聊天室业务-群聊

创建群聊

@ChannelHandler.Sharable
public class GroupCreateRequestMessageHandler extends SimpleChannelInboundHandler<GroupCreateRequestMessage> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, GroupCreateRequestMessage msg) throws Exception {String groupName = msg.getGroupName();Set<String> members = msg.getMembers();// 群管理器GroupSession groupSession = GroupSessionFactory.getGroupSession();Group group = groupSession.createGroup(groupName, members);if (group == null) {// 发生成功消息ctx.writeAndFlush(new GroupCreateResponseMessage(true, groupName + "创建成功"));// 发送拉群消息List<Channel> channels = groupSession.getMembersChannel(groupName);for (Channel channel : channels) {channel.writeAndFlush(new GroupCreateResponseMessage(true, "您已被拉入" + groupName));}} else {ctx.writeAndFlush(new GroupCreateResponseMessage(false, groupName + "已经存在"));}}
}

群聊

@ChannelHandler.Sharable
public class GroupChatRequestMessageHandler extends SimpleChannelInboundHandler<GroupChatRequestMessage> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, GroupChatRequestMessage msg) throws Exception {List<Channel> channels = GroupSessionFactory.getGroupSession().getMembersChannel(msg.getGroupName());for (Channel channel : channels) {channel.writeAndFlush(new GroupChatResponseMessage(msg.getFrom(), msg.getContent()));}}
}

加入群聊

@ChannelHandler.Sharable
public class GroupJoinRequestMessageHandler extends SimpleChannelInboundHandler<GroupJoinRequestMessage> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, GroupJoinRequestMessage msg) throws Exception {Group group = GroupSessionFactory.getGroupSession().joinMember(msg.getGroupName(), msg.getUsername());if (group != null) {ctx.writeAndFlush(new GroupJoinResponseMessage(true, msg.getGroupName() + "群加入成功"));} else {ctx.writeAndFlush(new GroupJoinResponseMessage(true, msg.getGroupName() + "群不存在"));}}
}

退出群聊

@ChannelHandler.Sharable
public class GroupQuitRequestMessageHandler extends SimpleChannelInboundHandler<GroupQuitRequestMessage> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, GroupQuitRequestMessage msg) throws Exception {Group group = GroupSessionFactory.getGroupSession().removeMember(msg.getGroupName(), msg.getUsername());if (group != null) {ctx.writeAndFlush(new GroupJoinResponseMessage(true, "已退出群" + msg.getGroupName()));} else {ctx.writeAndFlush(new GroupJoinResponseMessage(true, msg.getGroupName() + "群不存在"));}}
}

查看成员

@ChannelHandler.Sharable
public class GroupMembersRequestMessageHandler extends SimpleChannelInboundHandler<GroupMembersRequestMessage> {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, GroupMembersRequestMessage msg) throws Exception {Set<String> members = GroupSessionFactory.getGroupSession().getMembers(msg.getGroupName());ctx.writeAndFlush(new GroupMembersResponseMessage(members));}
}

3.5 聊天室业务-退出

@Slf4j
@ChannelHandler.Sharable
public class QuitHandler extends ChannelInboundHandlerAdapter {// 当连接断开时触发 inactive 事件@Overridepublic void channelInactive(ChannelHandlerContext ctx) throws Exception {SessionFactory.getSession().unbind(ctx.channel());log.debug("{} 已经断开", ctx.channel());}// 当出现异常时触发@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {SessionFactory.getSession().unbind(ctx.channel());log.debug("{} 已经异常断开 异常是{}", ctx.channel(), cause.getMessage());}
}

3.6 聊天室业务-空闲检测

连接假死

原因

• 网络设备出现故障，例如网卡，机房等，底层的 TCP 连接已经断开了，但应用程序没有感知到，仍然占用着资源。
• 公网网络不稳定，出现丢包。如果连续出现丢包，这时现象就是客户端数据发不出去，服务端也一直收不到数据，就这么一直耗着
• 应用程序线程阻塞，无法进行数据读写

问题

• 假死的连接占用的资源不能自动释放
• 向假死的连接发送数据，得到的反馈是发送超时

服务器端解决

• 怎么判断客户端连接是否假死呢？如果能收到客户端数据，说明没有假死。因此策略就可以定为，每隔一段时间就检查这段时间内是否接收到客户端数据，没有就可以判定为连接假死

// 用来判断是不是 读空闲时间过长，或 写空闲时间过长
// 5s 内如果没有收到 channel 的数据，会触发一个 IdleState#READER_IDLE 事件
ch.pipeline().addLast(new IdleStateHandler(5, 0, 0));
// ChannelDuplexHandler 可以同时作为入站和出站处理器
ch.pipeline().addLast(new ChannelDuplexHandler() {// 用来触发特殊事件@Overridepublic void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception{IdleStateEvent event = (IdleStateEvent) evt;// 触发了读空闲事件if (event.state() == IdleState.READER_IDLE) {log.debug("已经 5s 没有读到数据了");ctx.channel().close();}}
});

客户端定时心跳

• 客户端可以定时向服务器端发送数据，只要这个时间间隔小于服务器定义的空闲检测的时间间隔，那么就能防止前面提到的误判，客户端可以定义如下心跳处理器

// 用来判断是不是 读空闲时间过长，或 写空闲时间过长
// 3s 内如果没有向服务器写数据，会触发一个 IdleState#WRITER_IDLE 事件
ch.pipeline().addLast(new IdleStateHandler(0, 3, 0));
// ChannelDuplexHandler 可以同时作为入站和出站处理器
ch.pipeline().addLast(new ChannelDuplexHandler() {// 用来触发特殊事件@Overridepublic void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception{IdleStateEvent event = (IdleStateEvent) evt;// 触发了写空闲事件if (event.state() == IdleState.WRITER_IDLE) {// log.debug("3s 没有写数据了，发送一个心跳包");ctx.writeAndFlush(new PingMessage());}}
});