Netty 是一个利用 Java 的高级网络的能力，隐藏其背后的复杂性而提供一个易于使用的API的客户端/服务器框架。

可能在此之前你没有接触过，不过不要担心，下面我们通过一个消息推送的例子来看一下netty是怎么使用的。

1.添加Maven依赖

 io.nettynetty-all4.1.36.Final

2.设置主启动类

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplication
public class MessageSendApplication {public static void main(String[] args) {SpringApplication.run(MessageSendApplication.class, args);try {new NettyServer(12345).start();System.out.println("https://blog.csdn.net/moshowgame");System.out.println("http://127.0.0.1:6688/netty-websocket/index");} catch (Exception e) {System.out.println("NettyServerError:" + e.getMessage());}}
}

3.NettyServer

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.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
import io.netty.handler.stream.ChunkedWriteHandler;/*** NettyServer Netty服务器配置*/
public class NettyServer {private final int port;public NettyServer(int port) {this.port = port;}public void start() throws Exception {EventLoopGroup bossGroup = new NioEventLoopGroup();EventLoopGroup group = new NioEventLoopGroup();try {ServerBootstrap sb = new ServerBootstrap();sb.option(ChannelOption.SO_BACKLOG, 1024);sb.group(group, bossGroup) // 绑定线程池.channel(NioServerSocketChannel.class) // 指定使用的channel.localAddress(this.port)// 绑定监听端口.childHandler(new ChannelInitializer() { // 绑定客户端连接时候触发操作@Overrideprotected void initChannel(SocketChannel ch) throws Exception {System.out.println("收到新连接");//websocket协议本身是基于http协议的，所以这边也要使用http解编码器ch.pipeline().addLast(new HttpServerCodec());//以块的方式来写的处理器ch.pipeline().addLast(new ChunkedWriteHandler());ch.pipeline().addLast(new HttpObjectAggregator(8192));ch.pipeline().addLast(new WebSocketServerProtocolHandler("/ws", null, true, 65536 * 10));ch.pipeline().addLast(new WebSocketHandler());}});ChannelFuture cf = sb.bind().sync(); // 服务器异步创建绑定System.out.println(NettyServer.class + " 启动正在监听： " + cf.channel().localAddress());cf.channel().closeFuture().sync(); // 关闭服务器通道} finally {group.shutdownGracefully().sync(); // 释放线程池资源bossGroup.shutdownGracefully().sync();}}
}

4.MyChannelHandlerPool

通道组池，管理所有websocket连接

import io.netty.channel.group.ChannelGroup;
import io.netty.channel.group.DefaultChannelGroup;
import io.netty.util.concurrent.GlobalEventExecutor;/*** MyChannelHandlerPool* 通道组池，管理所有websocket连接*/
public class MyChannelHandlerPool {public MyChannelHandlerPool(){}public static ChannelGroup channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);}

5.WebSocketHandler

处理ws以下几种情况：

• channelActive与客户端建立连接
• channelInactive与客户端断开连接
• channelRead0客户端发送消息处理

import cn.hutool.json.JSONObject;
import cn.hutool.json.JSONUtil;
import com.example.messagesend.netty.NettyConfig;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
import io.netty.util.AttributeKey;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;@Component
@ChannelHandler.Sharable
@Slf4j
public class WebSocketHandler extends SimpleChannelInboundHandler {/*** 一旦连接，第一个被执行*/@Overridepublic void handlerAdded(ChannelHandlerContext ctx) throws Exception {log.info("有新的客户端链接：[{}]", ctx.channel().id().asLongText());// 添加到channelGroup 通道组NettyConfig.getChannelGroup().add(ctx.channel());}/*** 读取数据*/@Overrideprotected void channelRead0(ChannelHandlerContext ctx, TextWebSocketFrame msg) throws Exception {log.info("服务器收到消息：{}", msg.text());// 获取用户ID,关联channelString text = msg.text();String uid = text.split(":")[0];String message = text.split(":")[1];
//        JSONObject jsonObject = JSONUtil.parseObj(msg.text());NettyConfig.getChannelMap().put(uid, ctx.channel());// 将用户ID作为自定义属性加入到channel中，方便随时channel中获取用户IDAttributeKey key = AttributeKey.valueOf("userId");ctx.channel().attr(key).setIfAbsent(uid);// 回复消息ctx.channel().writeAndFlush(new TextWebSocketFrame(uid+"："+message));}@Overridepublic void handlerRemoved(ChannelHandlerContext ctx) throws Exception {log.info("用户下线了:{}", ctx.channel().id().asLongText());// 删除通道NettyConfig.getChannelGroup().remove(ctx.channel());removeUserId(ctx);}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {log.info("异常：{}", cause.getMessage());// 删除通道NettyConfig.getChannelGroup().remove(ctx.channel());removeUserId(ctx);ctx.close();}/*** 删除用户与channel的对应关系*/private void removeUserId(ChannelHandlerContext ctx) {AttributeKey key = AttributeKey.valueOf("userId");String userId = ctx.channel().attr(key).get();NettyConfig.getChannelMap().remove(userId);}
}

6.Netty配置

管理全局Channel以及用户对应的channel（推送消息）

import io.netty.channel.Channel;
import io.netty.channel.group.ChannelGroup;
import io.netty.channel.group.DefaultChannelGroup;
import io.netty.util.concurrent.GlobalEventExecutor;import java.util.concurrent.ConcurrentHashMap;public class NettyConfig {/*** 定义全局单利channel组 管理所有channel*/private static volatile ChannelGroup channelGroup = null;/*** 存放请求ID与channel的对应关系*/private static volatile ConcurrentHashMap channelMap = null;/*** 定义两把锁*/private static final Object lock1 = new Object();private static final Object lock2 = new Object();public static ChannelGroup getChannelGroup() {if (null == channelGroup) {synchronized (lock1) {if (null == channelGroup) {channelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);}}}return channelGroup;}public static ConcurrentHashMap getChannelMap() {if (null == channelMap) {synchronized (lock2) {if (null == channelMap) {channelMap = new ConcurrentHashMap<>();}}}return channelMap;}public static Channel getChannel(String userId) {if (null == channelMap) {return getChannelMap().get(userId);}return channelMap.get(userId);}
}

7.socket.html

ID 
TEXT 

 
服务端返回的应答消息

8.Controller

写好了html当然还需要一个controller来引导页面。

import cn.hutool.core.util.RandomUtil;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.ModelAndView;@RestController
public class TestController {@GetMapping("/index")public ModelAndView index() {ModelAndView mav = new ModelAndView("socket");mav.addObject("uid", RandomUtil.randomNumbers(6));return mav;}
}

下面我们打开页面测试一下

9.改造netty支持url参数

我们重新写一个WebSocketHandler:MyWebSocketHandler，然后调整加载handler的顺序,优先MyWebSocketHandler在WebSocketServerProtocolHandler之上。

改造MyWebSocketHandler的channelRead方法，首次连接会是一个FullHttpRequest类型，可以通过FullHttpRequest.uri()获取完整ws的URL地址，之后接受信息的话，会是一个TextWebSocketFrame类型。

MyWebSocketHandler:

import com.alibaba.fastjson.JSON;
import com.example.messagesend.netty.MyChannelHandlerPool;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.handler.codec.http.FullHttpRequest;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;import java.util.HashMap;
import java.util.Map;public class MyWebSocketHandler extends SimpleChannelInboundHandler {@Overridepublic void channelActive(ChannelHandlerContext ctx) throws Exception {System.out.println("与客户端建立连接，通道开启！");//添加到channelGroup通道组MyChannelHandlerPool.channelGroup.add(ctx.channel());}@Overridepublic void channelInactive(ChannelHandlerContext ctx) throws Exception {System.out.println("与客户端断开连接，通道关闭！");//添加到channelGroup 通道组MyChannelHandlerPool.channelGroup.remove(ctx.channel());}@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {//首次连接是FullHttpRequest，处理参数 by zhengkai.blog.csdn.netif (null != msg && msg instanceof FullHttpRequest) {FullHttpRequest request = (FullHttpRequest) msg;String uri = request.uri();Map paramMap=getUrlParams(uri);System.out.println("接收到的参数是："+ JSON.toJSONString(paramMap));//如果url包含参数，需要处理if(uri.contains("?")){String newUri=uri.substring(0,uri.indexOf("?"));System.out.println(newUri);request.setUri(newUri);}}else if(msg instanceof TextWebSocketFrame){//正常的TEXT消息类型TextWebSocketFrame frame=(TextWebSocketFrame)msg;System.out.println("客户端收到服务器数据：" +frame.text());sendAllMessage(frame.text());}super.channelRead(ctx, msg);}@Overrideprotected void channelRead0(ChannelHandlerContext channelHandlerContext, TextWebSocketFrame textWebSocketFrame) throws Exception {}private void sendAllMessage(String message){//收到信息后，群发给所有channelMyChannelHandlerPool.channelGroup.writeAndFlush( new TextWebSocketFrame(message));}private static Map getUrlParams(String url){Map map = new HashMap<>();url = url.replace("?",";");if (!url.contains(";")){return map;}if (url.split(";").length > 0){String[] arr = url.split(";")[1].split("&");for (String s : arr){String key = s.split("=")[0];String value = s.split("=")[1];map.put(key,value);}return  map;}else{return map;}}
}

然后在 NettyServer中调整顺序：

我们html中的socket连接地址也需要改一下：

socket = new WebSocket("ws://127.0.0.1:12345/ws?uid=666&gid=777");

接着重新运行一下，看看我们控制台的效果：