本文主要是介绍【Netty4】深入学习Netty，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
Netty is an asynchronous event-driven network application framework
for rapid development of maintainable high performance protocol servers & clients
学习前，建议了解下java NIO相关知识，有助于对Netty中对象的理解。
NIO介绍，博客地址：https://blog.csdn.net/the_fool_/article/details/83000648
AIO、BIO、NIO的区别，博客地址：https://blog.csdn.net/anxpp/article/details/51512200
Netty如何封装Java NIO，博客地址：：https://blog.csdn.net/tjreal/article/details/79751342
应用场景：https://blog.csdn.net/LIAN_XL/article/details/79799072
官网：https://netty.io/
版本：目前最新版本为4.1.30
环境：JDK 5 (Netty 3.x) or 6 (Netty 4.x) is enough
八卦：Netty5被干掉的原因？极大增加了复杂度，效率却没有提升，作者干掉了master分支。
模块，结构：
支持的链接类型：普通链接、长连接、心跳检测等。
使用：官方的简单demo，用于介绍Netty 创建过程：
完整代码：https://blog.csdn.net/the_fool_/article/details/80611148
1、根据实际业务创建handle处理类，处理客户端请求实际信息：
package com.xxx.ann.netty.mostsimple;import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.ReferenceCountUtil;/*** Handles a server-side channel.* 实际上自定义的业务流程使用的是本类*/
public class DiscardServerHandler extends ChannelInboundHandlerAdapter { // (1)/*** Server读取信息的方法* @param ctx* @param msg*/@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) {ByteBuf in = (ByteBuf) msg;try {while (in.isReadable()) { // (1)System.out.print((char) in.readByte());System.out.flush();}// 向客户端发送消息String response = "hello client!";// 在当前场景下，发送的数据必须转换成ByteBuf数组ByteBuf encoded = ctx.alloc().buffer(4 * response.length());encoded.writeBytes(response.getBytes());ctx.write(encoded);ctx.flush();} finally {ReferenceCountUtil.release(msg); // (2)}}/*** 处理异常* @param ctx* @param cause*/@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) { // (4)// Close the connection when an exception is raised.cause.printStackTrace();ctx.close();}
}2、Server 端代码：
package com.xxx.ann.netty.mostsimple;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;/*** server 端*/
public class DiscardServer {private int port;public DiscardServer(int port){this.port=port;}public void run() throws Exception{/**EventLoopGroup:IO操作的多线程组*boss:* accepts an incoming connection 处理链接*worker:* handles the traffic of the accepted connection once* the boss accepts the connection and registers the accepted* connection to the worker 处理实际逻辑* 使用多少线程以及如何将它们映射到创建的通道取决于EventLoopGroup实现，甚至可以通过构造函数进行配置。* */EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup workerGroup = new NioEventLoopGroup();try {/**ServerBootstrap是一个建立服务器的助手类。可以直接使用通道设置服务器。*/ServerBootstrap b = new ServerBootstrap();b.group(bossGroup, workerGroup)/**Here, we specify to use the NioServerSocketChannel class which is used to* instantiate a new Channel to accept incoming connections.*/.channel(NioServerSocketChannel.class)/**** 这里指定处理程序将始终由新接受的通道进行处理* ChannelInitializer：是专门帮助用户配置新通道的特殊处理程序。* 实际使用需要抽取到顶级类并自定义业务逻辑代码*/.childHandler(new ChannelInitializer<SocketChannel>() {@Overridepublic void initChannel(SocketChannel ch) throws Exception {ch.pipeline().addLast(new DiscardServerHandler());}})/**特定通道实现参数，具体含义：https://netty.io/4.1/api/io/netty/channel/ChannelOption.html*option() is for the NioServerSocketChannel that accepts incoming connections* childOption() is for the Channels accepted by the parent ServerChannel* */.option(ChannelOption.SO_BACKLOG, 128).childOption(ChannelOption.SO_KEEPALIVE, true);/** Bind and start to accept incoming connections.*/ChannelFuture f = b.bind(port).sync();/*** Wait until the server socket is closed.* In this example, this does not happen, but you can do that to gracefully* shut down your server.* */f.channel().closeFuture().sync();} catch (InterruptedException e) {e.printStackTrace();}finally {workerGroup.shutdownGracefully();bossGroup.shutdownGracefully();}}public static void main(String[] args) throws Exception {int port=8081;new DiscardServer(port).run();}
}
3、浏览器进入licalhost:8081或者telnet localhost 8081可访问服务端，可在控制台查看到已经建立连接并访问成功（本demo不会成功返回数据）。
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