很早之前就看过李林峰写的netty的书,但是感觉没有直接用到还是理解不够深入,现在的公司有两套自己基于Netty开发的系统,感觉才真正理解为啥要这么做
借用别人文章回顾下 https://www.cnblogs.com/carl10086/p/6183030.html
健壮性、功能、性能(预置了选多的编码功能,支持多种主流协议)、可定制性(通过ChannelHandler对通信框架进行灵活的扩展)和可扩展性
由于一个完整的包会被TCP拆分为多个包进行发送,也有可能将多个小的包封装成一个大包进行发送,所以会出现粘包、拆包的问题
例子将msg转换为Netty的ByteBuf对象,通过ByteBuf的readableBytes获取缓冲区可读的字节数,根据可读的字节数创建byte数组。将缓冲区的内容读取到byte数组中
问题的解决方法:定长,加开始结束符号,消息头包含长度消息体存储消息等
下面是解决了和未解决的代码,注释掉的是有包问题的代码,解决问题的主要是增加了两个Handler如下描述
package com.netty.helloword; import io.netty.bootstrap.ServerBootstrap; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelInitializer; import io.netty.channel.ChannelOption; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.SocketChannel; import io.netty.channel.socket.nio.NioServerSocketChannel; import io.netty.handler.codec.LineBasedFrameDecoder; import io.netty.handler.codec.string.StringDecoder; public class Server { public void bind(int port) throws Exception { EventLoopGroup bossGroup = new NioEventLoopGroup(); EventLoopGroup workerGroup = new NioEventLoopGroup(); try { ServerBootstrap serverBootstrap = new ServerBootstrap(); serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class) .option(ChannelOption.SO_BACKLOG, 1024).option(ChannelOption.SO_KEEPALIVE, true) .childHandler(new ChildChannelHandler()); ChannelFuture f = serverBootstrap.bind(port).sync(); System.out.println("Server start"); f.channel().closeFuture().sync(); } finally { bossGroup.shutdownGracefully(); workerGroup.shutdownGracefully(); System.out.println("release..."); } } private class ChildChannelHandler extends ChannelInitializer<SocketChannel> { @Override protected void initChannel(SocketChannel ch) throws Exception { ch.pipeline().addLast(new LineBasedFrameDecoder(1024)); ch.pipeline().addLast(new StringDecoder()); ch.pipeline().addLast(new ServerHandler()); } } public static void main(String[] args) throws Exception { int port = 9998; new Server().bind(port); } }
package com.netty.helloword; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerAdapter; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; public class ServerHandler extends ChannelInboundHandlerAdapter { private int counter; @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { // ByteBuf buf = (ByteBuf) msg; // byte[] req = new byte[buf.readableBytes()]; // buf.readBytes(req); // String body = new String(req, "UTF-8").substring(0, req.length // - System.getProperty("line.separator").length()); String body = (String) msg; System.out.println("The time server receive order : " + body + " ; the counter is : " + ++counter); String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body) ? new java.util.Date(System.currentTimeMillis()).toString() : "BAD ORDER"; currentTime = currentTime + System.getProperty("line.separator"); ByteBuf resp = Unpooled.copiedBuffer(currentTime.getBytes()); ctx.writeAndFlush(resp); } @Override public void channelReadComplete(ChannelHandlerContext ctx) throws Exception { ctx.flush(); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { ctx.close(); } }
package com.netty.helloword; import io.netty.bootstrap.Bootstrap; import io.netty.channel.ChannelFuture; import io.netty.channel.ChannelInitializer; import io.netty.channel.ChannelOption; import io.netty.channel.EventLoopGroup; import io.netty.channel.nio.NioEventLoopGroup; import io.netty.channel.socket.SocketChannel; import io.netty.channel.socket.nio.NioSocketChannel; import io.netty.handler.codec.LineBasedFrameDecoder; import io.netty.handler.codec.string.StringDecoder; public class Client { public void connect(int port, String host) throws Exception { EventLoopGroup group = new NioEventLoopGroup(); try { Bootstrap b = new Bootstrap(); b.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true) .handler(new ChannelInitializer<SocketChannel>() { @Override public void initChannel(SocketChannel ch) throws Exception { ch.pipeline().addLast(new LineBasedFrameDecoder(1024)); ch.pipeline().addLast(new StringDecoder()); ch.pipeline().addLast(new ClientChannelHandler()); } }); ChannelFuture f = b.connect(host, port).sync(); f.channel().closeFuture().sync(); } finally { group.shutdownGracefully(); } } private class ClientChannelHandler extends ChannelInitializer<SocketChannel> { @Override protected void initChannel(SocketChannel ch) throws Exception { ch.pipeline().addLast(new ClientHandler()); } } public static void main(String[] args) throws Exception { new Client().connect(9998, "127.0.0.1"); } }
package com.netty.helloword; import io.netty.buffer.ByteBuf; import io.netty.buffer.Unpooled; import io.netty.channel.ChannelHandlerAdapter; import io.netty.channel.ChannelHandlerContext; import io.netty.channel.ChannelInboundHandlerAdapter; import io.netty.util.ReferenceCountUtil; public class ClientHandler extends ChannelInboundHandlerAdapter { // private final ByteBuf firstMessage; private int counter; private byte[] req; public ClientHandler() { // byte[] req = "QUERY TIME ORDER".getBytes(); // firstMessage = Unpooled.buffer(req.length); // firstMessage.writeBytes(req); req = ("QUERY TIME ORDER" + System.getProperty("line.separator")).getBytes(); } @Override public void channelActive(ChannelHandlerContext ctx) { // ctx.writeAndFlush(firstMessage); ByteBuf message = null; for (int i = 0; i < 100; i++) { message = Unpooled.buffer(req.length); message.writeBytes(req); ctx.writeAndFlush(message); } } @Override public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception { // ByteBuf buf = (ByteBuf) msg; // byte[] req = new byte[buf.readableBytes()]; // buf.readBytes(req); // String body = new String(req, "UTF-8"); String body = (String) msg; System.out.println("Now is : " + body); } @Override public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { ctx.close(); } }
LineBasedFrameDecoder:
(1) 遍历ByteBuf中的可读字节,判断看是否有" "或者" ",如果有,就以此为结束位置,从可读索引到结束位置区间的字节就组成了一行
(2) 是一个以换行符为结束标志的解码器,支持携带结束符或者不携带结束符2种方式,同时支持配置单行的最大长度。
(3) 超过单行最大长度直接抛异常
StringDecoder:
(1) 将接收的对象转换为字符串
(2) 继续调用后面的Handler
DelimiterBasedFrameDecoder:
自定义特殊符号分割,有2个参数,一个为单行最大长度,一个为自定义符号对象
FixedLengthFrameDecoder:
定长切分
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提供了对于序列化反序列化的各种支持,因为各种序列化方式的速度和大小差距较大,所以可以根据需要提高性能
ch.pipeline().addLast("frameDecoder", new LengthFieldBasedFrameDecoder(65535, 0, 2, 0, 2)); ch.pipeline().addLast("msgpack decoder", new MsgpackDecoder()); ch.pipeline().addLast("frameEncoder", new LengthFieldPrepender(2)); ch.pipeline().addLast("msgpack encoder", new MsgpackEncoder());
ch.pipeline().addLast(new ProtobufVarint32FrameDecoder()); ch.pipeline().addLast(new ProtobufDecoder(SubscribeReqProto.SubscribeReq.getDefaultInstance())); ch.pipeline().addLast(new ProtobufVarint32LengthFieldPrepender()); ch.pipeline().addLast(new ProtobufEncoder()); ch.pipeline().addLast(new SubReqServerHandler());
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Http/JSON/Websocket服务器相关支持,上面文章中的例子已经非常清楚了
ch.pipeline().addLast("http-decoder", new HttpRequestDecoder()); // 请求消息解码器 ch.pipeline().addLast("http-aggregator", new HttpObjectAggregator(65536));// 目的是将多个消息转换为单一的request或者response对象 ch.pipeline().addLast("http-encoder", new HttpResponseEncoder());//响应解码器 ch.pipeline().addLast("http-chunked", new ChunkedWriteHandler());//目的是支持异步大文件传输()
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为什么要开发私有协议栈
由于现代软件的复杂性,一个大型软件系统往往会被人为地拆分称为多个模块,另外随着移动互联网的兴起,网站的规模越来越大,业务功能越来越多,往往需要集群和分布式部署。模块之间的通信就需要进行跨节点通信。
传统的Java应用中节点通信的常用方式:
- rmi远程服务调用
- Java Socket + Java序列化
- RPC框架 Thrift、Apache的Avro等
- 利用标准的公有协议进行跨节点调用,例如HTTP+XML,Restful+JSON或WebService
下面使用Netty设计私有协议
除了链路层的物理连接外,还需要对请求和响应消息进行编解码。 在请求和应答之外,还需要控制和管理类指令,例如链路建立的握手信息,链路检测的心跳信息。这些功能组合到一起后,就会形成私有协议。
- 每个Netty节点(Netty进程)之间建立长连接,使用Netty协议进行通信。
- Netty节点没有客户端和服务端的区别,谁首先发起连接,谁就是客户端。
协议栈功能描述:
- 基于Netty的NIO通信框架,提供高性能的异步通信能力;
- 提供消息的编解码框架,实现POJO的序列化和反序列化
- 提供基于IP地址的白名单接入认证机制;
- 链路的有效性校验机制;
- 链路的断线重连机制;
具体步骤:
- Netty协议栈客户端发送握手请求信息,携带节点ID等有效身份认证信息;
- Netty协议服务端对握手请求消息进行合法性校验,包括节点ID有效性校验、节点重复登录校验和IP地址合法性校验,校验通过后,返回登录成功的握手应答消息;
- 链路建立成功之后,客户端发送业务消息;
- 链路成功之后,服务端发送心跳消息;
- 链路建立成功之后,客户端发送心跳消息;
- 链路建立成功之后,服务端发送业务消息;
- 服务端退出时,服务端关闭连接,客户端感知对方关闭连接后,被动关闭客户端连接。