Netty03——进阶
创始人
2024-03-19 04:16:58
目录
- 1.粘包与半包
- 1.1.粘包现象
- 1.2.半包现象
- 1.3.现象分析
- 1.4 解决方案
- 1.4.1.短链接
- 1.4.2.固定长度
- 1.4.3.固定分隔符
- 1.4.4.预设长度
- 2.协议设计与解析
- 2.1.为什么需要协议？
- 2.2.redis 协议举例
- 2.3.http 协议举例
- 2.4.自定义协议要素
- 2.5.编解码器
- 3.聊天室案例
- 3.1.聊天室业务-介绍
- 3.2.聊天室业务-登录
- 3.3.聊天室业务-单聊
- 3.4.聊天室业务-群聊
- 3.5.聊天室业务-退出
- 3.6.聊天室业务-空闲检测
本文笔记整理来自尚硅谷视频https://www.bilibili.com/video/BV1py4y1E7oA/?p=91，相关资料可在视频评论区进行获取。
1.粘包与半包
1.1.粘包现象
服务端代码
package cn.itcast.netty.c6;import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
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 org.slf4j.Logger;
import org.slf4j.LoggerFactory;public class HelloWorldServer {static final Logger log = LoggerFactory.getLogger(HelloWorldServer.class);void start() {NioEventLoopGroup boss = new NioEventLoopGroup();NioEventLoopGroup worker = new NioEventLoopGroup();try {ServerBootstrap serverBootstrap = new ServerBootstrap();serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.group(boss, worker);serverBootstrap.childHandler(new ChannelInitializer() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));}});ChannelFuture channelFuture = serverBootstrap.bind(8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("server error", e);} finally {boss.shutdownGracefully();worker.shutdownGracefully();log.debug("stopped");}}public static void main(String[] args) {new HelloWorldServer().start();}
}
客户端代码
package cn.itcast.netty.c6;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 org.slf4j.Logger;
import org.slf4j.LoggerFactory;public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);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() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connected...");ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@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("localhost", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}
客户端代码希望发送 10 个消息，每个消息是 16 字节。
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。
09:57:22 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x4a255176, L:/127.0.0.1:8080 - R:/127.0.0.1:57554] REGISTERED
09:57:22 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x4a255176, L:/127.0.0.1:8080 - R:/127.0.0.1:57554] ACTIVE
09:57:22 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x4a255176, L:/127.0.0.1:8080 - R:/127.0.0.1:57554] 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 |................|
+--------+-------------------------------------------------+----------------+
09:57:22 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x4a255176, L:/127.0.0.1:8080 - R:/127.0.0.1:57554] READ COMPLETE
1.2.半包现象
（1）客户端代码希望发送 1 个消息，这个消息是 160 字节。
（2）为现象明显，服务端修改一下接收缓冲区，其它代码不变。
serverBootstrap.option(ChannelOption.SO_RCVBUF, 10);
（3）服务器端的某次输出，可以看到接收的消息被分为 5 节。
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] REGISTERED
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] ACTIVE
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] 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 |.... |
+--------+-------------------------------------------------+----------------+
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ COMPLETE
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ: 40B+-------------------------------------------------+| 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 |........ |
+--------+-------------------------------------------------+----------------+
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ COMPLETE
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ: 40B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 0c 0d 0e 0f 00 01 02 03 04 05 06 07 08 09 0a 0b |................|
|00000010| 0c 0d 0e 0f 00 01 02 03 04 05 06 07 08 09 0a 0b |................|
|00000020| 0c 0d 0e 0f 00 01 02 03 |........ |
+--------+-------------------------------------------------+----------------+
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ COMPLETE
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ: 40B+-------------------------------------------------+| 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 |........ |
+--------+-------------------------------------------------+----------------+
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ COMPLETE
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ: 4B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 0c 0d 0e 0f |.... |
+--------+-------------------------------------------------+----------------+
10:02:17 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0x6a59a227, L:/127.0.0.1:8080 - R:/127.0.0.1:51403] READ COMPLETE
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
（1）粘包现象
- 现象，发送 abc def，接收 abcdef
- 原因：
- 应用层：接收方 ByteBuf 设置太大（Netty 默认 1024）；
- 滑动窗口：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：会造成粘包，一次性尽可能多地发送数据；
（2）半包现象
- 现象，发送 abcdef，接收 abc def
- 原因：
- 应用层：接收方 ByteBuf 小于实际发送数据量；
- 滑动窗口：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：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；
（3）本质是因为 TCP 是流式协议，消息无边界。
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。
- 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。
- 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；
1.4.1.短链接
（1）以解决粘包为例，客户端代码如下：
public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);public static void main(String[] args) {for (int i = 0; i < 10; i++) {send();}System.out.println("finish...");}private static void send() {NioEventLoopGroup worker = new NioEventLoopGroup();try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer() {@Overrideprotected void initChannel(SocketChannel ch) {log.debug("connected...");ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx){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);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();}}
}
服务器端代码注释掉 serverBootstrap.option(ChannelOption.SO_RCVBUF, 10); 这行语句。输出如下：
（2）用这种办法还是不能解决半包问题，因为接收方的缓冲区大小是有限的。
//对于服务器端，调整 netty 的接收缓冲区 (byteBuf)
serverBootstrap.childOption(ChannelOption.RCVBUF_ALLOCATOR, new AdaptiveRecvByteBufAllocator(16, 16, 16));
//对于客户端，一次发送 18 个字节的数据（超出了 netty 的接收缓冲区的 16 字节大小）
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, 16, 17});ctx.writeAndFlush(buffer);ctx.channel().close();
}
此时在进行测试便会发生半包现象。
1.4.2.固定长度
让所有数据包长度固定（假设长度为 8 字节），服务器端加入：
ch.pipeline().addLast(new FixedLengthFrameDecoder(8));
客户端测试代码，注意, 采用这种方法后，客户端什么时候 flush 都可以。
public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);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() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connetted...");ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");// 发送内容随机的数据包Random r = new Random();char c = 'a';ByteBuf buffer = ctx.alloc().buffer();for (int i = 0; i < 10; i++) {byte[] bytes = new byte[8];for (int j = 0; j < r.nextInt(8); j++) {bytes[j] = (byte) c;}c++;buffer.writeBytes(bytes);}ctx.writeAndFlush(buffer);}});}});ChannelFuture channelFuture = bootstrap.connect("192.168.0.103", 9090).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}
客户端输出如下：
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2] REGISTERED
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2] CONNECT: /192.168.0.103:9090
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] ACTIVE
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] WRITE: 80B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 61 61 61 00 00 00 00 62 00 00 00 00 00 00 00 |aaaa....b.......|
|00000010| 63 63 00 00 00 00 00 00 64 00 00 00 00 00 00 00 |cc......d.......|
|00000020| 00 00 00 00 00 00 00 00 66 66 66 66 00 00 00 00 |........ffff....|
|00000030| 67 67 67 00 00 00 00 00 68 00 00 00 00 00 00 00 |ggg.....h.......|
|00000040| 69 69 69 69 69 00 00 00 6a 6a 6a 6a 00 00 00 00 |iiiii...jjjj....|
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x3c2ef3c2, L:/192.168.0.103:53155 - R:/192.168.0.103:9090] FLUSH
服务器端输出如下：
12:06:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xe3d9713f] binding...
12:06:51 [DEBUG] [main] c.i.n.HelloWorldServer - [id: 0xe3d9713f, L:/192.168.0.103:9090] bound...
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] REGISTERED
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] ACTIVE
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] c.i.n.HelloWorldServer - connected [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155]
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 61 61 61 00 00 00 00 |aaaa.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 00 00 00 00 00 00 00 |b....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 63 63 00 00 00 00 00 00 |cc...... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 64 00 00 00 00 00 00 00 |d....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 00 00 00 00 00 00 00 00 |........ |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 66 66 66 66 00 00 00 00 |ffff.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 67 67 67 00 00 00 00 00 |ggg..... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 00 00 00 00 00 00 00 |h....... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 69 69 69 69 00 00 00 |iiiii... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ: 8B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6a 6a 6a 6a 00 00 00 00 |jjjj.... |
+--------+-------------------------------------------------+----------------+
12:07:00 [DEBUG] [nioEventLoopGroup-3-1] i.n.h.l.LoggingHandler - [id: 0xd739f137, L:/192.168.0.103:9090 - R:/192.168.0.103:53155] READ COMPLETE
该方法的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；
1.4.3.固定分隔符
服务端加入，默认以 \n 或 \r\n 作为分隔符，如果超出指定长度仍未出现分隔符，则抛出异常。
ch.pipeline().addLast(new LineBasedFrameDecoder(1024));
客户端在每条消息之后，加入 \n 分隔符。
public class HelloWorldClient {static final Logger log = LoggerFactory.getLogger(HelloWorldClient.class);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() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {log.debug("connetted...");ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {log.debug("sending...");Random r = new Random();char c = 'a';ByteBuf buffer = ctx.alloc().buffer();for (int i = 0; i < 10; i++) {for (int j = 1; j <= r.nextInt(16) + 1; j++) {buffer.writeByte((byte) c);}//换行符的 ASCII 值就是 10buffer.writeByte(10);c++;}ctx.writeAndFlush(buffer);}});}});ChannelFuture channelFuture = bootstrap.connect("localhost", 8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("client error", e);} finally {worker.shutdownGracefully();}}
}
客户端输出如下：
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - connetted...
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755] REGISTERED
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755] CONNECT: /192.168.0.103:9090
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] ACTIVE
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] c.i.n.HelloWorldClient - sending...
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] WRITE: 60B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 0a 62 62 62 0a 63 63 63 0a 64 64 0a 65 65 65 |a.bbb.ccc.dd.eee|
|00000010| 65 65 65 65 65 65 65 0a 66 66 0a 67 67 67 67 67 |eeeeeee.ff.ggggg|
|00000020| 67 67 0a 68 68 68 68 0a 69 69 69 69 69 69 69 0a |gg.hhhh.iiiiiii.|
|00000030| 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 0a |jjjjjjjjjjj. |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0x1282d755, L:/192.168.0.103:63641 - R:/192.168.0.103:9090] FLUSH
服务端输出如下：
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] c.i.n.HelloWorldServer - connected [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641]
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 1B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 61 |a |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 3B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 62 62 62 |bbb |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 3B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 63 63 63 |ccc |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 2B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 64 64 |dd |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 10B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 65 65 65 65 65 65 65 65 65 65 |eeeeeeeeee |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 2B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 66 66 |ff |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 7B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 67 67 67 67 67 67 67 |ggggggg |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 4B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 68 68 68 68 |hhhh |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 7B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 69 69 69 69 69 69 69 |iiiiiii |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] READ: 11B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a 6a |jjjjjjjjjjj |
+--------+-------------------------------------------------+----------------+
14:08:18 [DEBUG] [nioEventLoopGroup-3-5] i.n.h.l.LoggingHandler - [id: 0xa4b3be43, L:/192.168.0.103:9090 - R:/192.168.0.103:63641] 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。
1.4.4.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。
/** lengthFieldOffset = 1 (= the length of HDR1) : 长度偏移量是 1 个字节，即跳过开始的 HDR1 * lengthFieldLength = 2 : 长度表示占 2 个字节，即下面的 0x000C* lengthAdjustment = 1 (= the length of HDR2) : 调整一个字节，即从 Length 开始跳过一个字节才开始读取真正的消息* initialBytesToStrip = 3 (= the length of HDR1 + LEN) : 剥离 3 个字节，即去掉 HDR1 + Length ** BEFORE DECODE (16 bytes) AFTER DECODE (13 bytes)* +------+--------+------+----------------+ +------+----------------+* | HDR1 | Length | HDR2 | Actual Content |----->| HDR2 | Actual Content |* | 0xCA | 0x000C | 0xFE | "HELLO, WORLD" | | 0xFE | "HELLO, WORLD" |* +------+--------+------+----------------+ +------+----------------+*
*/// 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));
使用 EmbeddedChannel 进行测试。
public class TestLengthFieldDecoder {public static void main(String[] args) {EmbeddedChannel channel = new EmbeddedChannel(new LengthFieldBasedFrameDecoder(1024, 0, 4, 1, 5),new LoggingHandler(LogLevel.DEBUG));// 4 个字节的长度内容 + 1 个字节的版本号 + 实际内容ByteBuf buffer = ByteBufAllocator.DEFAULT.buffer();send(buffer, "Hello, world");send(buffer, "Hi");channel.writeInbound(buffer);}private static void send(ByteBuf buffer, String content) {//实际要发送的内容byte[] bytes = content.getBytes();//实际内容长度int length = bytes.length;buffer.writeInt(length);buffer.writeByte(1); //额外加入版本号buffer.writeBytes(bytes);}
}
输出结果如下：
10:37:40 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] REGISTERED
10:37:40 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] ACTIVE
10:37:40 [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 |
+--------+-------------------------------------------------+----------------+
10:37:40 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ: 2B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 48 69 |Hi |
+--------+-------------------------------------------------+----------------+
10:37:40 [DEBUG] [main] i.n.h.l.LoggingHandler - [id: 0xembedded, L:embedded - R:embedded] READ COMPLETEProcess finished with exit code 0
2.协议设计与解析
2.1.为什么需要协议？
（1）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。
（2）例如：在网络上传输
下雨天留客天留我不留
这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。
① 一种解读：
下雨天留客，天留，我不留
② 另一种解读：
下雨天，留客天，留我不？留
（3）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
NioEventLoopGroup worker = new NioEventLoopGroup();
byte[] LINE = {13, 10};
try {Bootstrap bootstrap = new Bootstrap();bootstrap.channel(NioSocketChannel.class);bootstrap.group(worker);bootstrap.handler(new ChannelInitializer() {@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) {set(ctx);get(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);ctx.writeAndFlush(buf);}@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {ByteBuf buf = (ByteBuf) msg;System.out.println("读取 redis 返回的消息：");System.out.println(buf.toString(Charset.defaultCharset()));}});}});//连接 redisChannelFuture channelFuture = bootstrap.connect("192.168.88.100", 6379).sync();channelFuture.channel().closeFuture().sync();
} catch (InterruptedException e) {log.error("client error", e);
} finally {worker.shutdownGracefully();
}
结果如下：
10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd] REGISTERED
10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd] CONNECT: /192.168.88.100:6379
10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd, L:/192.168.88.1:53631 - R:/192.168.88.100:6379] ACTIVE
10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd, L:/192.168.88.1:53631 - R:/192.168.88.100:6379] WRITE: 37B+-------------------------------------------------+| 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 34 0d |*3..$3..set..$4.|
|00000010| 0a 6e 61 6d 65 0d 0a 24 38 0d 0a 7a 68 61 6e 67 |.name..$8..zhang|
|00000020| 73 61 6e 0d 0a |san.. |
+--------+-------------------------------------------------+----------------+
10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd, L:/192.168.88.1:53631 - R:/192.168.88.100:6379] FLUSH
10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd, L:/192.168.88.1:53631 - R:/192.168.88.100:6379] WRITE: 23B+-------------------------------------------------+| 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 34 0d |*2..$3..get..$4.|
|00000010| 0a 6e 61 6d 65 0d 0a |.name.. |
+--------+-------------------------------------------------+----------------+
10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd, L:/192.168.88.1:53631 - R:/192.168.88.100:6379] FLUSH
10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd, L:/192.168.88.1:53631 - R:/192.168.88.100:6379] READ: 19B+-------------------------------------------------+| 0 1 2 3 4 5 6 7 8 9 a b c d e f |
+--------+-------------------------------------------------+----------------+
|00000000| 2b 4f 4b 0d 0a 24 38 0d 0a 7a 68 61 6e 67 73 61 |+OK..$8..zhangsa|
|00000010| 6e 0d 0a |n.. |
+--------+-------------------------------------------------+----------------+
读取 redis 返回的消息：
+OK
$8
zhangsan10:11:49 [DEBUG] [nioEventLoopGroup-2-1] i.n.h.l.LoggingHandler - [id: 0xc75993bd, L:/192.168.88.1:53631 - R:/192.168.88.100:6379] READ COMPLETE
此时 Redis 中的数据如下：
有关 Redis 的相关知识，可以查看Redis6——入门介绍这篇文章。
2.3.http 协议举例
@Slf4j
public class TestHttp {public static void main(String[] args) {NioEventLoopGroup boss = new NioEventLoopGroup();NioEventLoopGroup worker = new NioEventLoopGroup();try {ServerBootstrap serverBootstrap = new ServerBootstrap();serverBootstrap.channel(NioServerSocketChannel.class);serverBootstrap.group(boss, worker);serverBootstrap.childHandler(new ChannelInitializer() {@Overrideprotected void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new LoggingHandler(LogLevel.DEBUG));//配置 http 编解码器ch.pipeline().addLast(new HttpServerCodec());//对上面的编解码器的结果进行处理ch.pipeline().addLast(new SimpleChannelInboundHandler() {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, HttpRequest msg) throws Exception {log.debug("{}", msg.getClass());//获取请求log.debug("{}", msg.uri());QueryStringDecoder decoder = new QueryStringDecoder(msg.uri());List name = decoder.parameters().get("name");//相应对象DefaultFullHttpResponse response = new DefaultFullHttpResponse(msg.protocolVersion(), HttpResponseStatus.OK);byte[] bytes = ("hello, world!
").getBytes();response.headers().setInt(HttpHeaderNames.CONTENT_LENGTH, bytes.length);response.content().writeBytes(bytes);//写回相应ctx.writeAndFlush(response);}});/*ch.pipeline().addLast(new ChannelInboundHandlerAdapter() {@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {log.debug("{}", msg.getClass());if (msg instanceof HttpRequest) {} else if (msg instanceof HttpContent) {}}});*/}});ChannelFuture channelFuture = serverBootstrap.bind(8080).sync();channelFuture.channel().closeFuture().sync();} catch (InterruptedException e) {log.error("server error", e);} finally {boss.shutdownGracefully();worker.shutdownGracefully();}}
}
在浏览器地址栏中输入以下内容，然后页面会显示服务器端相应的内容，即代码中的"hello, world!"
http://localhost:8080/index.html
此时服务器端的部分输出如下：
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；
2.5.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。
package cn.itcast.message;import lombok.Data;import java.io.Serializable;
import java.util.HashMap;
import java.util.Map;@Data
public abstract class Message implements Serializable {/*** 根据消息类型字节，获得对应的消息 class* @param messageType 消息类型字节* @return 消息 class*/public static Class getMessageClass(int messageType) {return messageClasses.get(messageType);}private int sequenceId;private int messageType;public abstract int getMessageType();public static final int LoginRequestMessage = 0;public static final int LoginResponseMessage = 1;public static final int ChatRequestMessage = 2;public static final int ChatResponseMessage = 3;public static final int GroupCreateRequestMessage = 4;public static final int GroupCreateResponseMessage = 5;public static final int GroupJoinRequestMessage = 6;public static final int GroupJoinResponseMessage = 7;public static final int GroupQuitRequestMessage = 8;public static final int GroupQuitResponseMessage = 9;public static final int GroupChatRequestMessage = 10;public static final int GroupChatResponseMessage = 11;public static final int GroupMembersRequestMessage = 12;public static final int GroupMembersResponseMessage = 13;public static final int PingMessage = 14;public static final int PongMessage = 15;/*** 请求类型 byte 值*/public static final int RPC_MESSAGE_TYPE_REQUEST = 101;/*** 响应类型 byte 值*/public static final int RPC_MESSAGE_TYPE_RESPONSE = 102;private static final Map> messageClasses = new HashMap<>();static {messageClasses.put(LoginRequestMessage, LoginRequestMessage.class);messageClasses.put(LoginResponseMessage, LoginResponseMessage.class);messageClasses.put(ChatRequestMessage, ChatRequestMessage.class);messageClasses.put(ChatResponseMessage, ChatResponseMessage.class);messageClasses.put(GroupCreateRequestMessage, GroupCreateRequestMessage.class);messageClasses.put(GroupCreateResponseMessage, GroupCreateResponseMessage.class);messageClasses.put(GroupJoinRequestMessage, GroupJoinRequestMessage.class);messageClasses.put(GroupJoinResponseMessage, GroupJoinResponseMessage.class);messageClasses.put(GroupQuitRequestMessage, GroupQuitRequestMessage.class);messageClasses.put(GroupQuitResponseMessage, GroupQuitResponseMessage.class);messageClasses.put(GroupChatRequestMessage, GroupChatRequestMessage.class);messageClasses.put(GroupChatResponseMessage, GroupChatResponseMessage.class);messageClasses.put(GroupMembersRequestMessage, GroupMembersRequestMessage.class);messageClasses.put(GroupMembersResponseMessage, GroupMembersResponseMessage.class);messageClasses.put(RPC_MESSAGE_TYPE_REQUEST, RpcRequestMessage.class);messageClasses.put(RPC_MESSAGE_TYPE_RESPONSE, RpcResponseMessage.class);}
}
package cn.itcast.message;import lombok.Data;
import lombok.ToString;@Data
@ToString(callSuper = true)
public class LoginRequestMessage extends Message {private String username;private String password;private String nickname;public LoginRequestMessage() {}public LoginRequestMessage(String username, String password, String nickname) {this.username = username;this.password = password;this.nickname = nickname;}public LoginRequestMessage(String username, String password) {this.username = username;this.password = password;}@Overridepublic int getMessageType() {return LoginRequestMessage;}
}
@Slf4j
public class MessageCodec extends ByteToMessageCodec {@Overrideprotected 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);}@Overrideprotected void decode(ChannelHandlerContext ctx, ByteBuf in, List 测试如下：
package cn.itcast.protocol;import cn.itcast.message.LoginRequestMessage;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.LoggingHandler;public class TestMessageCodec {public static void main(String[] args) throws Exception {EmbeddedChannel channel = new EmbeddedChannel(//帧解码器new LengthFieldBasedFrameDecoder(1024, 12, 4, 0, 0),new LoggingHandler(),new MessageCodec());// encodeLoginRequestMessage message = new LoginRequestMessage("zhangsan", "123", "张三");channel.writeOutbound(message);// decodeByteBuf buf = ByteBufAllocator.DEFAULT.buffer();new MessageCodec().encode(null, message, buf);//入站//channel.writeInbound(buf);//测试 LengthFieldBasedFrameDecoderByteBuf buf1 = buf.slice(0, 100);ByteBuf buf2 = buf.slice(100, buf.readableBytes() - 100);channel.writeInbound(buf1); // release 0buf1.retain(); //引用计数 + 1channel.writeInbound(buf2);}
}
解读：
💡 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，它们的构造方法对 @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 {@Overrideprotected void encode(ChannelHandlerContext ctx, Message msg, List 3.聊天室案例
3.1.聊天室业务-介绍
（1）用户管理接口
/*** 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);
}
（2）会话管理接口
/*** 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);
}
（3）聊天组会话管理接口
/*** 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 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 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 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() {@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() {@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() {@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 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 {@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 {@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 {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, GroupCreateRequestMessage msg) throws Exception {String groupName = msg.getGroupName();Set 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 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 {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, GroupChatRequestMessage msg) throws Exception {List 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 {@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 {@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 {@Overrideprotected void channelRead0(ChannelHandlerContext ctx, GroupMembersRequestMessage msg) throws Exception {Set 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());}}
});
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