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一、前言

本系列内容为阅读《Netty4 核心原理》一书内容总结，内容存在个人删改，仅做个人笔记使用。

本篇涉及内容 ：第四章 基于 Netty 手写 Tomcat、第五章 基于 Netty 重构 RPC 框架

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本系列内容基于 Netty 4.1.73.Final 版本，如下：

 <dependency><groupId>io.netty</groupId><artifactId>netty-all</artifactId><version>4.1.73.Final</version></dependency>

系列文章目录：
TODO

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二、 基于 Netty 实现 Tomcat

Netty 作为底层通信框架，也可以用于实现 Web 容器。

Tomcat 时基于 J2EE规范的 Web 容器，主要入口是 web.xml 文件。web.xml 文件中主要配置 Servlet、Filter、Listener 等，而 Servlet、Filter、Listener 在 J2EE 中只是抽象的实现，具体业务逻辑由开发者实现。

下面用传统 IO 和 Netty 的方式分别简单实现 Tomcat 的功能

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至此为止准备工作就已经就绪，下面我们按照传统 IO 和 Netty 的方式分别实现 Tomcat 的功能。

1. 基于传统 IO 重构 Tomcat

1.1 创建 MyRequest 和 MyReponse 对象

@Slf4j
@Getter
public class MyRequest {private String uri;private String method;public MyRequest(InputStream inputStream) throws IOException {BufferedReader bufferedReader =new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));String line = bufferedReader.readLine();if (StringUtils.isNotBlank(line)) {String[] split = line.split("\\s");this.method = split[0];this.uri = split[1].split("\\?")[0];}}
}public class MyResponse {private OutputStream outputStream;public MyResponse(OutputStream outputStream) {this.outputStream = outputStream;}public void write(String content) throws IOException {//按照HTTP响应报文的格式写入String httpResponse = "HTTP/1.1 200 OK\n" +"Content-Type:text/html\n" +"\r\n" +content;outputStream.write(httpResponse.getBytes());}
}

1.2 构建一个基础的 Servlet

public abstract class MyServlet {public void service(MyRequest request, MyResponse response) throws Exception {if(request.getMethod().equals("GET")){doGet(request, response);}else if(request.getMethod().equals("POST")){doPost(request, response);}}public abstract void doGet(MyRequest request, MyResponse response) throws Exception;public abstract void doPost(MyRequest request, MyResponse response) throws Exception;
}

1.3 创建用户业务代码

public class FirstServlet extends MyServlet {@Overridepublic void doGet(MyRequest request, MyResponse response) throws Exception {this.doPost(request, response);}@Overridepublic void doPost(MyRequest request, MyResponse response) throws Exception {response.write("FirstServlet");}
}public class SecondServlet extends MyServlet {@Overridepublic void doGet(MyRequest request, MyResponse response) throws Exception {this.doPost(request, response);}@Overridepublic void doPost(MyRequest request, MyResponse response) throws Exception {response.write("SecondServlet");}
}

1.4 完成web.properties 配置

这里为了简化操作，使用 web.properties 来替代 web.xml 文件，如下：

servlet.one.url=/firstServlet.do
servlet.one.className=com.kingfish.netty.unit4.tomcat.FirstServletservlet.two.url=/secondServlet.do
servlet.two.className=com.kingfish.netty.unit4.tomcat.SecondServlet

1.5 创建 Tomcat 启动类

@Slf4j
public class MyTomcat {private int port = 8080;private ServerSocket server;private Map<String, MyServlet> servletMap = Maps.newHashMap();private Properties webxml = new Properties();@SneakyThrowsprivate void init() {String webInf = Objects.requireNonNull(this.getClass().getResource("/")).getPath();webxml.load(this.getClass().getResourceAsStream("/web.properties"));for (Object k : webxml.keySet()) {final String key = k.toString();if (key.endsWith(".url")) {String serverName = key.replaceAll("\\.url", "");String url = webxml.getProperty(key);String className = webxml.getProperty(serverName + ".className");MyServlet servlet = (MyServlet) Class.forName(className).newInstance();servletMap.put(url, servlet);}}}@SneakyThrowspublic void start() {// 1. 初始化。加载配置，初始化 servletMapinit();// 初始化服务server = new ServerSocket(port);System.out.println("服务启动成功, 端口 : " + port);// 等待客户端连接while (!Thread.interrupted()) {// TODO : 实际要改为多线程process(server.accept());}}/*** 请求处理** @param client* @throws Exception*/private void process(Socket client) throws Exception {try (InputStream inputStream = client.getInputStream();OutputStream outputStream = client.getOutputStream();) {MyRequest request = new MyRequest(inputStream);MyResponse response = new MyResponse(outputStream);String uri = request.getUri();if (servletMap.containsKey(uri)) {servletMap.get(uri).service(request, response);} else {response.write("404 - Not Found");}outputStream.flush();} catch (Exception e) {log.error("[请求异常]", e);} finally {client.close();}}public static void main(String[] args) {new MyTomcat().start();}
}

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通过请求 http://localhost:8080/firstServlet.do 和 http://localhost:8080/sencondServlet.do 可以得到相应结果。如下：

2. 基于 Netty 重构 Tomcat

2.1 创建 NettyRequest和 NettyResponse 对象

public class NettyRequest {private ChannelHandlerContext ctx;private HttpRequest request;public NettyRequest(ChannelHandlerContext ctx, HttpRequest request) {this.ctx = ctx;this.request = request;}public String getUri() {return request.uri();}public String getMethod() {return request.method().name();}public Map<String, List<String>> getParameters() {QueryStringDecoder decoder = new QueryStringDecoder(getUri());return decoder.parameters();}public String getParameter(String name) {final List<String> params = getParameters().get(name);return params == null ? null : params.get(0);}
}public class NettyResponse {private ChannelHandlerContext ctx;private HttpRequest request;public NettyResponse(ChannelHandlerContext ctx, HttpRequest request) {this.ctx = ctx;this.request = request;}public void write(String out) {try {if (out == null || out.length() == 0){return;}// 设置 HTTP 以及请求头信息DefaultFullHttpResponse response = new DefaultFullHttpResponse(// 设置版本为 HTTP 1.1HttpVersion.HTTP_1_1,// 设置响应状态码 200HttpResponseStatus.OK,// 设置输出内容编码格式 UTF-8Unpooled.wrappedBuffer(out.getBytes(StandardCharsets.UTF_8)));response.headers().set("Content-Type", "text/html;");ctx.write(response);} finally {ctx.flush();ctx.close();}}
}

2.2 构建一个基础的 Servlet

public abstract class NettyServlet {public void service(NettyRequest request, NettyResponse response) throws Exception {if(request.getMethod().equals("GET")){doGet(request, response);}else if(request.getMethod().equals("POST")){doPost(request, response);}}public abstract void doGet(NettyRequest request, NettyResponse response) throws Exception;public abstract void doPost(NettyRequest request, NettyResponse response) throws Exception;}

2.3 创建业务底代码

public class FirstServlet extends NettyServlet {@Overridepublic void doGet(NettyRequest request, NettyResponse response) throws Exception {doPost(request, response);}@Overridepublic void doPost(NettyRequest request, NettyResponse response) throws Exception {response.write("FirstServlet");}
}

2.4 完成web.properties 配置

这里为了简化操作，使用 web.properties 来替代 web.xml 文件，如下：

servlet.one.url=/firstServlet.do
servlet.one.className=com.kingfish.netty.unit4.netty.FirstServlet

2.5 创建业务逻辑处理类

public class TomcatHandler extends ChannelInboundHandlerAdapter {private Map<String, NettyServlet> servletMap;public TomcatHandler(Map<String, NettyServlet> servletMap) {this.servletMap = servletMap;}@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {if (msg instanceof HttpRequest) {HttpRequest httpRequest = (HttpRequest) msg;NettyRequest request = new NettyRequest(ctx, httpRequest);NettyResponse response = new NettyResponse(ctx, httpRequest);String uri = request.getUri();if (servletMap.containsKey(uri)) {servletMap.get(uri).service(request, response);} else {response.write("404 - Not Found");}}}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();}
}

2.6 创建 Tomcat 启动类

@Slf4j
public class NettyTomcat {private int port = 8080;private Map<String, NettyServlet> servletMap = Maps.newHashMap();private Properties webxml = new Properties();@SneakyThrowsprivate void init() {webxml.load(this.getClass().getResourceAsStream("/web.properties"));for (Object k : webxml.keySet()) {final String key = k.toString();if (key.endsWith(".url")) {String serverName = key.replaceAll("\\.url", "");String url = webxml.getProperty(key);String className = webxml.getProperty(serverName + ".className");NettyServlet servlet = (NettyServlet) Class.forName(className).newInstance();servletMap.put(url, servlet);}}}@SneakyThrowspublic void start() {// 1. 初始化。加载配置，初始化 servletMapinit();// 2. 创建 boss 和 worker 线程NioEventLoopGroup bossGroup = new NioEventLoopGroup();NioEventLoopGroup workerGroup = new NioEventLoopGroup();try {ServerBootstrap bootstrap = new ServerBootstrap();bootstrap.group(bossGroup, workerGroup)// 主线程处理类.channel(NioServerSocketChannel.class)// 子线程处理类.childHandler(new ChannelInitializer<SocketChannel>() {// 客户端初始化@Overrideprotected void initChannel(SocketChannel client) throws Exception {// Netty 对 Http 的封装，对顺序有要求// HttpResponseEncoder 解码器client.pipeline().addLast(new HttpResponseEncoder());// HttpRequestDecoder 编码器client.pipeline().addLast(new HttpRequestDecoder());// 业务逻辑处理client.pipeline().addLast(new TomcatHandler(servletMap));}})// 针对主线程配置 : 分配线程数量最大 128.option(ChannelOption.SO_BACKLOG, 128)// 针对子线程配置 保持长连接.childOption(ChannelOption.SO_KEEPALIVE, true);// 启动服务ChannelFuture channelFuture = bootstrap.bind(port).sync();System.out.println("服务启动成功, 端口 : " + port);// 阻塞主线程，防止直接执行 finally 中语句导致服务关闭，当有关闭事件到来时才会放行channelFuture.channel().closeFuture().sync();} finally {// 关闭线程池bossGroup.shutdownGracefully();workerGroup.shutdownGracefully();}}public static void main(String[] args) {new NettyTomcat().start();}

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通过请求 http://localhost:8080/firstServlet.do 可以得到相应结果。如下：

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三、基于 Netty 重构 RPC 框架

Netty 基本上是作为架构的底层存在，主要是完成高性能的网络通信。下面通过 Netty 简单实现 RPC框架的通信功能，整个项目结构如下图：

1. API 模块

1.1 定义 RPC API 接口

public interface HelloService {String sayHello(String name);
}

1.2 自定义传输协议

@Data
public class InvokerProtocol implements Serializable {/*** 类名*/private String className;/*** 方法名*/private String methodName;/*** 参数列表*/private Class<?>[] params;/*** 参数列表*/private Object[] values;
}

2. Provider 模块

2.1 实现 HelloService

public class HelloServiceImpl implements HelloService {@Overridepublic String sayHello(String name) {return name + ", Hello!";}
}

2.2 自定义 Netty 消息处理器

public class RegistryHandler extends ChannelInboundHandlerAdapter {private static Map<String, Object> registerMap = Maps.newConcurrentMap();private List<String> classNames = Lists.newArrayList();public RegistryHandler() {// 扫描指定目录下的提供者实例scannerClass("provider.provider");// 将提供者注册doRegister();}@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {InvokerProtocol invokerProtocol = (InvokerProtocol) msg;Object result = new Object();// 通过协议参数获取到具体提提供者，并通过反射调用if (registerMap.containsKey(invokerProtocol.getClassName())) {Object clazz = registerMap.get(invokerProtocol.getClassName());Method method = clazz.getClass().getMethod(invokerProtocol.getMethodName(), invokerProtocol.getParams());result = method.invoke(clazz, invokerProtocol.getValues());}ctx.write(result);ctx.flush();ctx.close();}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();ctx.close();}/*** 递归扫描** @param packageName*/private void scannerClass(String packageName) {URL url = this.getClass().getClassLoader().getResource(packageName.replaceAll("\\.", "/"));List<File> files = FileUtil.loopFiles(url.getFile(), pathname -> pathname.getName().endsWith(".class"));for (File file : files) {classNames.add(packageName + "." + file.getName().replace(".class", ""));}}@SneakyThrowsprivate void doRegister() {for (String className : classNames) {Class<?> clazz = Class.forName(className);Class<?> i = clazz.getInterfaces()[0];registerMap.put(i.getName(), clazz.getDeclaredConstructor().newInstance());}}
}

2.3 服务端启动

public class RpcRegister {private int port = 8090;@SneakyThrowspublic void start() {// 2. 创建 boss 和 worker 线程NioEventLoopGroup bossGroup = new NioEventLoopGroup();NioEventLoopGroup workerGroup = new NioEventLoopGroup();try {ServerBootstrap bootstrap = new ServerBootstrap();bootstrap.group(bossGroup, workerGroup)// 主线程处理类.channel(NioServerSocketChannel.class)// 子线程处理类.childHandler(new ChannelInitializer<SocketChannel>() {// 客户端初始化@Overrideprotected void initChannel(SocketChannel client) throws Exception {// 自定义协议解码器// LengthFieldBasedFrameDecoder 五个入参分别如下：// maxFrameLength : 框架的最大长度。如果帧长度大于此值，将抛出 TooLongFrameException// lengthFieldOffset : 长度属性的偏移量。即对应的长度属性在整个消息数据中的位置// lengthFieldLength : 长度属性的长度。如果长度属性是 int，那么这个值就是 4 (long 类型就是 8)// lengthAdjustment : 要添加到长度属性值的补偿值// initialBytesToStrip : 从解码帧中取出的第一个字节数。client.pipeline().addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));// 自定义协议编码器client.pipeline().addLast(new LengthFieldPrepender(4));// 对象参数类型编码器client.pipeline().addLast("encoder", new ObjectEncoder());// 对象参数类型解码器client.pipeline().addLast("decoder", new ObjectDecoder(Integer.MAX_VALUE, ClassResolvers.cacheDisabled(null)));client.pipeline().addLast(new RegistryHandler());}})// 针对主线程配置 : 分配线程数量最大 128.option(ChannelOption.SO_BACKLOG, 128)// 针对子线程配置 保持长连接.childOption(ChannelOption.SO_KEEPALIVE, true);// 启动服务ChannelFuture channelFuture = bootstrap.bind(port).sync();System.out.println("服务启动成功, 端口 : " + port);// 阻塞主线程，防止直接执行 finally 中语句导致服务关闭，当有关闭事件到来时才会放行channelFuture.channel().closeFuture().sync();} finally {// 关闭线程池bossGroup.shutdownGracefully();workerGroup.shutdownGracefully();}}public static void main(String[] args) {new RpcRegister().start();}
}

3. Consumer 模块

3.1 自定义 Netty 消息处理器

public class RpcProxyHandler extends ChannelInboundHandlerAdapter {@Getterprivate Object response;@Overridepublic void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {response = msg;}@Overridepublic void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {cause.printStackTrace();}
}

3.2 实现消费者端的代理调用

public class RpcProxy {/*** 创建代理对象** @param clazz* @param <T>* @return*/public static <T> T create(Class<?> clazz) {Class<?>[] interfaces = clazz.isInterface() ? new Class<?>[]{clazz} : clazz.getInterfaces();return (T) Proxy.newProxyInstance(clazz.getClassLoader(), interfaces, new MethodProxy(clazz));}/*** 方法代理*/public static class MethodProxy implements InvocationHandler {private Class<?> clazz;public MethodProxy(Class<?> clazz) {this.clazz = clazz;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {// 传进来的一个已实现的具体类，本次实现暂不处理该逻辑if (Object.class.equals(method.getDeclaringClass())) {return method.invoke(this, args);} else {// 如果传进来的是一个接口，则说明要进行 RPC 调用return rpcInvoke(proxy, method, args);}}/*** rpc 调用** @param proxy* @param method* @param args* @return* @throws InterruptedException*/private Object rpcInvoke(Object proxy, Method method, Object[] args) throws InterruptedException {NioEventLoopGroup group = new NioEventLoopGroup();RpcProxyHandler rpcProxyHandler = new RpcProxyHandler();try {// 传输协议封装InvokerProtocol invokerProtocol = new InvokerProtocol();invokerProtocol.setClassName(this.clazz.getName());invokerProtocol.setMethodName(method.getName());invokerProtocol.setValues(args);invokerProtocol.setParams(method.getParameterTypes());// 通过 netty 连接 服务提供者Bootstrap bootstrap = new Bootstrap();bootstrap.group(group).channel(NioSocketChannel.class).option(ChannelOption.TCP_NODELAY, true).handler(new ChannelInitializer<>() {@Overrideprotected void initChannel(Channel channel) throws Exception {// 自定义协议解码器// LengthFieldBasedFrameDecoder 五个入参分别如下：// maxFrameLength : 框架的最大长度。如果帧长度大于此值，将抛出 TooLongFrameException// lengthFieldOffset : 长度属性的偏移量。即对应的长度属性在整个消息数据中的位置// lengthFieldLength : 长度属性的长度。如果长度属性是 int，那么这个值就是 4 (long 类型就是 8)// lengthAdjustment : 要添加到长度属性值的补偿值// initialBytesToStrip : 从解码帧中取出的第一个字节数。channel.pipeline().addLast("frameDecoder", new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));// 自定义协议编码器channel.pipeline().addLast("frameEncoder", new LengthFieldPrepender(4));// 对象参数类型编码器channel.pipeline().addLast("encoder", new ObjectEncoder());// 对象参数类型解码器channel.pipeline().addLast("decoder", new ObjectDecoder(Integer.MAX_VALUE, ClassResolvers.cacheDisabled(null)));// 业务处理器channel.pipeline().addLast("handler", rpcProxyHandler);}});// 连接提供者服务并发送消息ChannelFuture future = bootstrap.connect(new InetSocketAddress("127.0.0.1", 8090)).sync();future.channel().writeAndFlush(invokerProtocol);// 阻塞主线程，防止直接执行 finally 中语句导致服务关闭，当有关闭事件到来时才会放行future.channel().closeFuture().sync();} finally {group.shutdownGracefully();}return rpcProxyHandler.getResponse();}}
}

3.3 消费者调用

public class RpcMain {public static void main(String[] args) {HelloService helloService = RpcProxy.create(HelloService.class);String hello = helloService.sayHello("张三");// 输出 hello = 张三, Hello!System.out.println("hello = " + hello);}
}

四、参考内容

1. https://www.cnblogs.com/kendoziyu/articles/why-selector-always-invoke-new-event.html
2. https://blog.csdn.net/wyaoyao93/article/details/114938670
3. https://blog.csdn.net/woaiwojialanxi/article/details/123602000