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
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
*/
@Override
public 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
*/
@Override
public 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>() {
@Override
public 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）。