Netty 是由 JBOSS 提供的一个 Java 开源框架。Netty 是一个基于 Java NIO 的开发框架，主要针对在 TCP 协议下，面向 Client 端的高并发应用，或者 Peer-to-Peer 场景下的大量数据持续传输的应用。
Netty 的特点：非阻塞、基于事件驱动、高性能、高可靠性和高可定制性。
Java 支持 3 种网络编程模型 I/O 模式：
(1) BIO (Blocking Input/Output): 同步并阻塞（传统阻塞型），服务器实现模式为一个连接一个线程，即客户端有连接请求时服务器端就需要启动一个线程进行处理，如果这个连接不做任何事情会造成不必要的线程开销；
(2) NIO (Non-blocking Input/Output): 同步非阻塞，服务器实现模式为一个线程处理多个请求（连接），即客户端发送的连接请求都会注册到多路复用器上，多路复用器轮询到连接有 I/O 请求就进行处理；
(3) AIO (Asynchronous Input/Output): 异步非阻塞，AIO 引入异步通道的概念，采用了 Proactor 模式，简化了程序编写，有效的请求才启动线程，它的特点是先由操作系统完成后才通知服务端程序启动线程去处理，一般适用于连接数较多且连接时间较长的应用。
各 I/O 模式的适用场景：
(1) BIO 方式适用于连接数目比较小且固定的架构，这种方式对服务器资源要求比较高，并发局限于应用中，JDK1.4 以前的唯一选择，但程序简单易理解；
(2) NIO 方式适用于连接数目多且连接比较短（轻操作）的架构，比如聊天服务器，弹幕系统，服务器间通讯等。编程比较复杂，JDK1.4 开始支持；
(3) AIO 方式使用于连接数目多且连接比较长（重操作）的架构，比如相册服务器，充分调用 OS 参与并发操作，编程比较复杂，JDK7 开始支持。
Netty: http://netty.io/
Netty GitHub: https://github.com/netty/netty
1. 开发环境
Windows版本：Windows 10 Home (20H2)
IntelliJ IDEA (https://www.jetbrains.com/idea/download/)：Community Edition for Windows 2020.1.4
Apache Maven (https://maven.apache.org/)：3.8.1
Redis for Windows：5.0.14
注：Spring 开发环境的搭建，可以参考 “ Spring基础知识（1）- Spring简介、Spring体系结构和开发环境配置 ”。
2. 创建 Spring Boot 基础项目
项目实例名称：SpringbootExample20
Spring Boot 版本：2.6.6
创建步骤：
(1) 创建 Maven 项目实例 SpringbootExample20；
(2) Spring Boot Web 配置；
(3) 导入 Thymeleaf 依赖包；
(4) 配置 jQuery；
具体操作请参考 “Spring 系列 (2) - 在 Spring Boot 项目里使用 Thymeleaf、JQuery+Bootstrap 和国际化” 里的项目实例 SpringbootExample02，文末包含如何使用 spring-boot-maven-plugin 插件运行打包的内容。
SpringbootExample20 和 SpringbootExample02 相比，SpringbootExample20 不配置 Bootstrap、模版文件（templates/*.html）和国际化。
3. 配置 Netty
1) 导入 Netty 依赖包
访问 http://www.mvnrepository.com/，查询 netty，修改 pom.xml
<project ... >
...
<dependencies>
...
<!-- Netty -->
<dependency>
<groupId>io.netty</groupId>
<artifactId>netty-all</artifactId>
<version>4.1.89.Final</version>
</dependency>
...
</dependencies>
...
</project>
在IDE中项目列表 -> SpringbootExample20 -> 点击鼠标右键 -> Maven -> Reload Project
2) 修改 src/main/resources/application.properties 文件，内容如下
spring.main.banner-mode=off
# Web server
server.display-name=SpringbootExample20-Test
server.address=localhost
server.port=9090
# Netty server
netty.websocket.ip=localhost
netty.websocket.port=9999
netty.websocket.max-frame-size=10240
netty.websocket.path=/ws
3) 创建 src/main/java/com/example/netty/NettyBootsrapRunner.java 文件
package com.example.netty;
import java.net.InetSocketAddress;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.ApplicationArguments;
import org.springframework.boot.ApplicationRunner;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.ApplicationListener;
import org.springframework.context.event.ContextClosedEvent;
import org.springframework.stereotype.Component;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelPipeline;
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.DefaultFullHttpResponse;
import io.netty.handler.codec.http.FullHttpRequest;
import io.netty.handler.codec.http.HttpObjectAggregator;
import io.netty.handler.codec.http.HttpResponseStatus;
import io.netty.handler.codec.http.HttpServerCodec;
import io.netty.handler.codec.http.HttpVersion;
import io.netty.handler.codec.http.websocketx.WebSocketServerProtocolHandler;
import io.netty.handler.codec.http.websocketx.extensions.compression.WebSocketServerCompressionHandler;
import io.netty.handler.stream.ChunkedWriteHandler;
@Component
public class NettyBootsrapRunner implements ApplicationRunner, ApplicationListener<ContextClosedEvent>, ApplicationContextAware {
@Value("${netty.websocket.port}")
private int port;
@Value("${netty.websocket.ip}")
private String ip;
@Value("${netty.websocket.path}")
private String path;
@Value("${netty.websocket.max-frame-size}")
private long maxFrameSize;
private ApplicationContext applicationContext;
private Channel serverChannel;
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
public void run(ApplicationArguments args) throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.group(bossGroup, workerGroup);
serverBootstrap.channel(NioServerSocketChannel.class);
serverBootstrap.localAddress(new InetSocketAddress(this.ip, this.port));
serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
ChannelPipeline pipeline = socketChannel.pipeline();
pipeline.addLast(new HttpServerCodec());
pipeline.addLast(new ChunkedWriteHandler());
pipeline.addLast(new HttpObjectAggregator(65536));
pipeline.addLast(new ChannelInboundHandlerAdapter() {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
if(msg instanceof FullHttpRequest) {
FullHttpRequest fullHttpRequest = (FullHttpRequest) msg;
String uri = fullHttpRequest.uri();
if (!uri.equals(path)) {
// Not websocket uri, return 404
ctx.channel().writeAndFlush(new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.NOT_FOUND))
.addListener(ChannelFutureListener.CLOSE);
return ;
}
}
super.channelRead(ctx, msg);
}
});
pipeline.addLast(new WebSocketServerCompressionHandler());
pipeline.addLast(new WebSocketServerProtocolHandler(path, null, true, maxFrameSize));
// Get handler from IOC
pipeline.addLast(applicationContext.getBean(WebsocketMessageHandler.class));
}
});
System.out.println("NettyBootsrapRunner -> run(): (" + this.ip + ":" + this.port + ")");
Channel channel = serverBootstrap.bind().sync().channel();
this.serverChannel = channel;
channel.closeFuture().sync();
} finally {
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
public void onApplicationEvent(ContextClosedEvent event) {
if (this.serverChannel != null) {
this.serverChannel.close();
}
System.out.println("NettyBootsrapRunner -> onApplicationEvent(): stop websocket");
}
}
4) 创建 src/main/java/com/example/netty/WebsocketMessageHandler.java 文件
package com.example.netty;
import org.springframework.stereotype.Component;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.handler.codec.http.websocketx.TextWebSocketFrame;
import io.netty.handler.codec.http.websocketx.WebSocketCloseStatus;
import io.netty.handler.codec.http.websocketx.WebSocketFrame;
@Sharable
@Component
public class WebsocketMessageHandler extends SimpleChannelInboundHandler<WebSocketFrame> {
@Override
protected void channelRead0(ChannelHandlerContext ctx, WebSocketFrame msg) throws Exception {
if (msg instanceof TextWebSocketFrame) {
TextWebSocketFrame textWebSocketFrame = (TextWebSocketFrame) msg;
// Reply to client
ctx.channel().writeAndFlush(new TextWebSocketFrame("Received your message -> " + textWebSocketFrame.text()));
} else {
// Invalid message type
ctx.channel().writeAndFlush(WebSocketCloseStatus.INVALID_MESSAGE_TYPE).addListener(ChannelFutureListener.CLOSE);
}
}
@Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
super.channelInactive(ctx);
System.out.println("WebsocketMessageHandler -> channelInactive(): " + ctx.channel().remoteAddress());
}
@Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
super.channelActive(ctx);
System.out.println("WebsocketMessageHandler -> channelActive(): " + ctx.channel().remoteAddress());
}
}
5) 运行
Edit Configurations
Click "+" add new configuration -> Select "Maven"
Command line: clean spring-boot:run
Name: SpringbootExample20 [clean,spring-boot:run]
-> Apply / OK
Click Run "SpringbootExample02 [clean,spring-boot:run]"
...
Spring boot example project
访问 http://localhost:9090/test
Test Page
注：打包可以将 Command line 改成 clean package spring-boot:repackage
4. 测试实例 (Web 模式)
1) 创建 src/main/resources/templates/client.html 文件
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta charset="UTF-8">
<title th:text="${var}">Client</title>
<script language="javascript" th:src="@{/lib/jquery/jquery-3.6.0.min.js}"></script>
</head>
<body>
<h4>Netty WebSocket - Client</h4>
<p> </p>
<p>
<label><strong>WebSocket url:</strong></label><br>
<input type="text" name="ws_url" id="ws_url" value="ws://localhost:9999/websocket" style="width: 50%; height: 32px;" /><br><br>
<button type="button" id="btn_connect" class="btn btn-default btn-sm">Connect</button>
<button type="button" id="btn_close" class="btn btn-default btn-sm" style="display: none;">Close</button>
</p>
<p id="message_area" style="display: none;">
<label><strong>Message:</strong></label><br>
<input type="text" name="message" id="message" style="width: 50%; height: 32px;" /><br><br>
<button type="button" id="btn_send" class="btn btn-default btn-sm">Send</button>
</p>
<p> </p>
<div id="result_area" style="padding: 15px; width: 50%; font-size: 12px; min-height: 120px;">
</div>
<script type="text/javascript">
var globalSocket = null;
$(document).ready(function() {
$("#btn_connect").click(function(e) {
connectWebSocket();
});
$("#btn_close").click(function(e) {
closeWebSocket();
});
$("#btn_send").click(function(e) {
if (globalSocket != null) {
var msg = $("#message").val();
if (msg == '') {
alert("Please enter message");
$("#message").focus();
return;
}
globalSocket.send(msg);
}
});
});
function connectWebSocket() {
var wsUrl = $("#ws_url").val();
if (wsUrl == '') {
alert("Please enter url");
$("#ws_url").focus();
return;
}
if (globalSocket == null) {
$("#result_area").html('');
$("#btn_execute").attr("disabled", "disabled");
createWebSocket(wsUrl);
}
}
function createWebSocket(url) {
if (globalSocket != null || url == '')
return;
console.log("createWebSocket(): url = ", url);
globalSocket = new WebSocket(url);
globalSocket.onopen = funcWSOpen;
globalSocket.onclose = funcWSClose;
globalSocket.onerror = funcWSError;
globalSocket.onmessage = funcWSMessage;
}
function closeWebSocket() {
if (globalSocket != null) {
console.log("closeWebSocket(): close");
globalSocket.close();
$("#btn_close").attr("disabled", "disabled");
$("#message_area").css("display", "none");
}
}
function funcWSOpen(e) {
console.log("funcWSOpen(): ", e);
$("#message_area").css("display", "");
$("#btn_close").removeAttr("disabled");
$("#btn_close").css("display", "");
$("#result_area").append("<br>WSOpen: Connected<br>");
}
function funcWSClose(e) {
console.log("funcWSClose(): ", e);
$("#result_area").append("<br>WSClose: Close<br>");
$("#btn_execute").removeAttr("disabled");
$("#btn_close").css("display", "none");
globalSocket = null;
}
function funcWSError(e) {
console.error("funcWSError(): ", e);
$("#result_area").append("<br>WSError: Error<br>");
$("#btn_execute").removeAttr("disabled");
$("#btn_close").css("display", "none");
globalSocket = null;
}
function funcWSMessage(e) {
console.log("funcWSMessage(): e.data = ", e.data);
$("#result_area").append("<br>WSMessage: " + e.data + "<br>");
}
</script>
</body>
</html>
2) 修改 src/main/java/com/example/controller/IndexController.java 文件
package com.example.controller;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
@Controller
public class IndexController {
@ResponseBody
@RequestMapping("/test")
public String test() {
return "Test Page";
}
@RequestMapping("/client")
public String client() {
return "client";
}
}
访问 http://localhost:9090/client，JAR 方式运行时，页面上 WebSocket url 是 ws://localhost:9999/websocket，点击 Connect 按钮测试。