V2AS问路
【Netty】一个RPC实例
阅读原文时间：2023年08月27日阅读：1

Netty实现简易RPC调用

总体流程：

  • 客户端发起rpc调用请求，封装好调用的接口名，函数名，返回类型，函数参数类型，函数参数值等属性，将消息发送给服务器。
  • 服务器的handler解析rpc请求，调用对应方法，并将方法结果写回客户端。
  • 客户端在主线程发送消息后，准备一个空 Promise 对象，用来接收结果。在客户端的RpcHandler解析完服务器发回的Rpc响应后，该Promise将被填充，客户端主线程根据Promise内的结果执行下一步操作。

在服务器的RpcRequestMessageHandler实现中，调用的接口类型写死为HelloService，后续可以改进。

1）准备工作

为了简化起见，在原来聊天项目的基础上新增 Rpc 请求和响应消息

@Data
public abstract class Message implements Serializable {

    // 省略旧的代码

    public static final int RPC_MESSAGE_TYPE_REQUEST = 101;
    public static final int  RPC_MESSAGE_TYPE_RESPONSE = 102;

    static {
        // ...
        messageClasses.put(RPC_MESSAGE_TYPE_REQUEST, RpcRequestMessage.class);
        messageClasses.put(RPC_MESSAGE_TYPE_RESPONSE, RpcResponseMessage.class);
    }

}

请求消息

@Getter
@ToString(callSuper = true)
public class RpcRequestMessage extends Message {

    /**
     * 调用的接口全限定名，服务端根据它找到实现
     */
    private String interfaceName;
    /**
     * 调用接口中的方法名
     */
    private String methodName;
    /**
     * 方法返回类型
     */
    private Class<?> returnType;
    /**
     * 方法参数类型数组
     */
    private Class[] parameterTypes;
    /**
     * 方法参数值数组
     */
    private Object[] parameterValue;

    public RpcRequestMessage(int sequenceId, String interfaceName, String methodName, Class<?> returnType, Class[] parameterTypes, Object[] parameterValue) {
        super.setSequenceId(sequenceId);
        this.interfaceName = interfaceName;
        this.methodName = methodName;
        this.returnType = returnType;
        this.parameterTypes = parameterTypes;
        this.parameterValue = parameterValue;
    }

    @Override
    public int getMessageType() {
        return RPC_MESSAGE_TYPE_REQUEST;
    }
}

响应消息

@Data
@ToString(callSuper = true)
public class RpcResponseMessage extends Message {
    /**
     * 返回值
     */
    private Object returnValue;
    /**
     * 异常值
     */
    private Exception exceptionValue;

    @Override
    public int getMessageType() {
        return RPC_MESSAGE_TYPE_RESPONSE;
    }
}

服务器架子

@Slf4j
public class RpcServer {
    public static void main(String[] args) {
        NioEventLoopGroup boss = new NioEventLoopGroup();
        NioEventLoopGroup worker = new NioEventLoopGroup();
        LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG);
        MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable();

        // rpc 请求消息处理器，待实现
        RpcRequestMessageHandler RPC_HANDLER = new RpcRequestMessageHandler();
        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.channel(NioServerSocketChannel.class);
            serverBootstrap.group(boss, worker);
            serverBootstrap.childHandler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new ProcotolFrameDecoder());
                    ch.pipeline().addLast(LOGGING_HANDLER);
                    ch.pipeline().addLast(MESSAGE_CODEC);
                    ch.pipeline().addLast(RPC_HANDLER);
                }
            });
            Channel channel = serverBootstrap.bind(8080).sync().channel();
            channel.closeFuture().sync();
        } catch (InterruptedException e) {
            log.error("server error", e);
        } finally {
            boss.shutdownGracefully();
            worker.shutdownGracefully();
        }
    }
}

客户端架子

public class RpcClient {
    public static void main(String[] args) {
        NioEventLoopGroup group = new NioEventLoopGroup();
        LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG);
        MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable();

        // rpc 响应消息处理器，待实现
        RpcResponseMessageHandler RPC_HANDLER = new RpcResponseMessageHandler();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.channel(NioSocketChannel.class);
            bootstrap.group(group);
            bootstrap.handler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new ProcotolFrameDecoder());
                    ch.pipeline().addLast(LOGGING_HANDLER);
                    ch.pipeline().addLast(MESSAGE_CODEC);
                    ch.pipeline().addLast(RPC_HANDLER);
                }
            });
            Channel channel = bootstrap.connect("localhost", 8080).sync().channel();
            channel.closeFuture().sync();
        } catch (Exception e) {
            log.error("client error", e);
        } finally {
            group.shutdownGracefully();
        }
    }
}

服务器端的 service 获取

public class ServicesFactory {

    static Properties properties;
    static Map<Class<?>, Object> map = new ConcurrentHashMap<>();

    static {
        try (InputStream in = Config.class.getResourceAsStream("/application.properties")) {
            properties = new Properties();
            properties.load(in);
            Set<String> names = properties.stringPropertyNames();
            for (String name : names) {
                if (name.endsWith("Service")) {
                    Class<?> interfaceClass = Class.forName(name);
                    Class<?> instanceClass = Class.forName(properties.getProperty(name));
                    map.put(interfaceClass, instanceClass.newInstance());
                }
            }
        } catch (IOException | ClassNotFoundException | InstantiationException | IllegalAccessException e) {
            throw new ExceptionInInitializerError(e);
        }
    }

    public static <T> T getService(Class<T> interfaceClass) {
        return (T) map.get(interfaceClass);
    }
}

相关配置 application.properties

serializer.algorithm=Json
cn.itcast.server.service.HelloService=cn.itcast.server.service.HelloServiceImpl

2）服务器 handler

@Slf4j
@ChannelHandler.Sharable
public class RpcRequestMessageHandler extends SimpleChannelInboundHandler<RpcRequestMessage> {

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, RpcRequestMessage message) {
        RpcResponseMessage response = new RpcResponseMessage();
        response.setSequenceId(message.getSequenceId());
        try {
            // 获取真正的实现对象
            HelloService service = (HelloService)
                    ServicesFactory.getService(Class.forName(message.getInterfaceName()));

            // 获取要调用的方法
            Method method = service.getClass().getMethod(message.getMethodName(), message.getParameterTypes());

            // 调用方法
            Object invoke = method.invoke(service, message.getParameterValue());
            // 调用成功
            response.setReturnValue(invoke);
        } catch (Exception e) {
            e.printStackTrace();
            // 调用异常
            response.setExceptionValue(e);
        }
        // 返回结果
        ctx.writeAndFlush(response);
    }
}

3）客户端代码第一版

只发消息

@Slf4j
public class RpcClient {
    public static void main(String[] args) {
        NioEventLoopGroup group = new NioEventLoopGroup();
        LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG);
        MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable();
        RpcResponseMessageHandler RPC_HANDLER = new RpcResponseMessageHandler();
        try {
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.channel(NioSocketChannel.class);
            bootstrap.group(group);
            bootstrap.handler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new ProcotolFrameDecoder());
                    ch.pipeline().addLast(LOGGING_HANDLER);
                    ch.pipeline().addLast(MESSAGE_CODEC);
                    ch.pipeline().addLast(RPC_HANDLER);
                }
            });
            Channel channel = bootstrap.connect("localhost", 8080).sync().channel();

            ChannelFuture future = channel.writeAndFlush(new RpcRequestMessage(
                    1,
                    "cn.itcast.server.service.HelloService",
                    "sayHello",
                    String.class,
                    new Class[]{String.class},
                    new Object[]{"张三"}
            )).addListener(promise -> {
                if (!promise.isSuccess()) {
                    Throwable cause = promise.cause();
                    log.error("error", cause);
                }
            });

            channel.closeFuture().sync();
        } catch (Exception e) {
            log.error("client error", e);
        } finally {
            group.shutdownGracefully();
        }
    }
}

4）客户端 handler 第一版

@Slf4j
@ChannelHandler.Sharable
public class RpcResponseMessageHandler extends SimpleChannelInboundHandler<RpcResponseMessage> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, RpcResponseMessage msg) throws Exception {
        log.debug("{}", msg);
    }
}

5）客户端代码 第二版

包括 channel 管理，代理，接收结果

@Slf4j
public class RpcClientManager {

    public static void main(String[] args) {
        HelloService service = getProxyService(HelloService.class);
        System.out.println(service.sayHello("zhangsan"));
//        System.out.println(service.sayHello("lisi"));
//        System.out.println(service.sayHello("wangwu"));
    }

    // 创建代理类
    public static <T> T getProxyService(Class<T> serviceClass) {
        ClassLoader loader = serviceClass.getClassLoader();
        Class<?>[] interfaces = new Class[]{serviceClass};
        //                                                            sayHello  "张三"
        Object o = Proxy.newProxyInstance(loader, interfaces, (proxy, method, args) -> {
            // 1. 将方法调用转换为 消息对象
            int sequenceId = SequenceIdGenerator.nextId();
            RpcRequestMessage msg = new RpcRequestMessage(
                    sequenceId,
                    serviceClass.getName(),
                    method.getName(),
                    method.getReturnType(),
                    method.getParameterTypes(),
                    args
            );
            // 2. 将消息对象发送出去
            getChannel().writeAndFlush(msg);

            // 3. 准备一个空 Promise 对象，来接收结果             指定 promise 对象异步接收结果线程
            DefaultPromise<Object> promise = new DefaultPromise<>(getChannel().eventLoop());
            RpcResponseMessageHandler.PROMISES.put(sequenceId, promise);

//            promise.addListener(future -> {
//                // 线程
//            });

            // 4. 等待 promise 结果
            promise.await();
            if(promise.isSuccess()) {
                // 调用正常
                return promise.getNow();
            } else {
                // 调用失败
                throw new RuntimeException(promise.cause());
            }
        });
        return (T) o;
    }

    private static Channel channel = null;
    private static final Object LOCK = new Object();

    // 获取唯一的 channel 对象
    public static Channel getChannel() {
        if (channel != null) {
            return channel;
        }
        synchronized (LOCK) { //  t2
            if (channel != null) { // t1
                return channel;
            }
            initChannel();
            return channel;
        }
    }

    // 初始化 channel 方法
    private static void initChannel() {
        NioEventLoopGroup group = new NioEventLoopGroup();
        LoggingHandler LOGGING_HANDLER = new LoggingHandler(LogLevel.DEBUG);
        MessageCodecSharable MESSAGE_CODEC = new MessageCodecSharable();
        RpcResponseMessageHandler RPC_HANDLER = new RpcResponseMessageHandler();
        Bootstrap bootstrap = new Bootstrap();
        bootstrap.channel(NioSocketChannel.class);
        bootstrap.group(group);
        bootstrap.handler(new ChannelInitializer<SocketChannel>() {
            @Override
            protected void initChannel(SocketChannel ch) throws Exception {
                ch.pipeline().addLast(new ProcotolFrameDecoder());
                ch.pipeline().addLast(LOGGING_HANDLER);
                ch.pipeline().addLast(MESSAGE_CODEC);
                ch.pipeline().addLast(RPC_HANDLER);
            }
        });
        try {
            channel = bootstrap.connect("localhost", 8080).sync().channel();
            channel.closeFuture().addListener(future -> {
                group.shutdownGracefully();
            });
        } catch (Exception e) {
            log.error("client error", e);
        }
    }
}

6）客户端 handler 第二版

@Slf4j
@ChannelHandler.Sharable
public class RpcResponseMessageHandler extends SimpleChannelInboundHandler<RpcResponseMessage> {

    //                       序号      用来接收结果的 promise 对象
    public static final Map<Integer, Promise<Object>> PROMISES = new ConcurrentHashMap<>();

    @Override

    protected void channelRead0(ChannelHandlerContext ctx, RpcResponseMessage msg) throws Exception {
        log.debug("{}", msg);
        // 拿到空的 promise
        Promise<Object> promise = PROMISES.remove(msg.getSequenceId());
        if (promise != null) {
            Object returnValue = msg.getReturnValue();
            Exception exceptionValue = msg.getExceptionValue();
            if(exceptionValue != null) {
                promise.setFailure(exceptionValue);
            } else {
                promise.setSuccess(returnValue);
            }
        }
    }
}

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