Netty 实现类似Dubbo的RPC

　　之前了解到dubbo 的底层是基于Netty，在学习了Netty 之后简单的模拟一个RPC。

　　模仿dubbo，消费者和提供者约定接口和协议，消费者远程调用提供者的服务，提供者返回一个字符串，消费者打印提供者返回的字符串

 1. HelloService 公共接口

package netty.rpc.publicinterface;

/**
 * 公共接口
 */
public interface HelloService {

    String hello(String name);
}

2. HelloServiceImpl 服务实现类

package netty.rpc.provider;

import netty.rpc.publicinterface.HelloService;

/**
 * 服务提供者实现类
 */
public class HelloServiceImpl implements HelloService {

    /**
     * 记录调用次数
     */
    private int count;

    @Override
    public String hello(String name) {
        count++;
        System.out.println("netty.rpc.server.HelloServiceImpl.hello, name: " + name + "; count: " + count);
        return " this is " + name + "; count: " + count;
    }
}

3.Netty 相关类

NettyServerHandler：

package netty.rpc.netty;


import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import netty.rpc.provider.HelloServiceImpl;
import netty.rpc.publicinterface.HelloService;
import org.apache.commons.lang.StringUtils;

public class NettyServerHandler extends ChannelInboundHandlerAdapter {

    private static final String PROTO = "helloservice://";
    private HelloService service = new HelloServiceImpl();

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        // 接收客户端的消息，并调用服务
        System.out.println("msg: " + msg);

        // 以约定的协议开头，就去掉协议之后调用serviceImpl 进行服务调用
        if (msg.toString().startsWith(PROTO)) {
            String param = StringUtils.substring(msg.toString(), PROTO.length());
            String result = service.hello(param);
            // 回显给客户端
            ctx.writeAndFlush(result);
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
}

NettyServer

package netty.rpc.netty;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

public class NettyServer {

    public static void start(String hostName, int port) {
        startService(hostName, port);
    }

    public static void startService(String hostname, int port) {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup(8);

        try {
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(new ChannelInitializer<SocketChannel>() {
                @Override
                protected void initChannel(SocketChannel ch) throws Exception {
                    ChannelPipeline pipeline = ch.pipeline();
                    pipeline.addLast(new StringDecoder());
                    pipeline.addLast(new StringEncoder());
                    // 自己的处理器
                    pipeline.addLast(new NettyServerHandler());
                }
            });
            ChannelFuture sync = serverBootstrap.bind(hostname, port).sync();
            sync.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                    if (future.isSuccess()) {
                        System.out.println("服务器启动成功, hostname: " + hostname + ", port: " + port);
                    }
                }
            });
            sync.channel().closeFuture().sync();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}

NettyClientHandler

package netty.rpc.netty;

import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

import java.util.concurrent.Callable;

public class NettyClientHandler extends ChannelInboundHandlerAdapter implements Callable {

    private ChannelHandlerContext channelHandlerContext;

    private String result;

    private String param;

    // 该方法第一次被调用(1)
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        channelHandlerContext = ctx;
    }

    // 4
    @Override
    public synchronized void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        result = msg.toString();
        notify();
    }

    // 3 - wait - 5
    @Override
    public synchronized Object call() throws Exception {
        channelHandlerContext.writeAndFlush(param);
        wait();
        return result;
    }

    // 2
    public void setParam(String param) {
        this.param = param;
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
        cause.printStackTrace();
    }
}

NettyClient

package netty.rpc.netty;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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.NioSocketChannel;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;

import java.lang.reflect.Proxy;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class NettyClient {

    // 执行器
    private static final ExecutorService executorService = Executors.newFixedThreadPool(Runtime.getRuntime().availableProcessors());

    private NettyClientHandler nettyClientHandler;

    // 使用代理模式获取对象(JDK 动态代理)= 执行过程实际是走Netty 调用服务
    public Object getBean(final Class serviceClazz, String proto) {
        return Proxy.newProxyInstance(Thread.currentThread().getContextClassLoader(), new Class[]{serviceClazz}, (proxy, method, param) -> {
            if (nettyClientHandler == null) {
                init();
            }

            // 设置参数为协议 + 参数 (服务器端会根据协议来解析到对应的参数然后来进行服务调用)
            nettyClientHandler.setParam(proto + param[0]);
            return executorService.submit(nettyClientHandler).get();
        });
    }

    private void init() {
        nettyClientHandler = new NettyClientHandler();
        EventLoopGroup workerGrop = new NioEventLoopGroup();
        Bootstrap bootstrap = new Bootstrap();
        bootstrap.group(workerGrop).channel(NioSocketChannel.class)
                .option(ChannelOption.TCP_NODELAY, true)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel ch) throws Exception {
                        ChannelPipeline pipeline = ch.pipeline();
                        pipeline.addLast(new StringDecoder());
                        pipeline.addLast(new StringEncoder());
                        pipeline.addLast(nettyClientHandler);
                    }
                });

        try {
            bootstrap.connect("127.0.0.1", 6666).sync();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

4. CustomerBootstrap 服务消费者

package netty.rpc.customer;

import netty.rpc.netty.NettyClient;
import netty.rpc.publicinterface.HelloService;

public class CustomerBootstrap {

    private static final String PROTO = "helloservice://";

    public static void main(String[] args) {
        // 创建一个消费者
        NettyClient nettyClient = new NettyClient();
        // 创建代理对象
        HelloService bean = (HelloService) nettyClient.getBean(HelloService.class, PROTO);
        for (int i = 0; i < 20; i++) {
            String hello = bean.hello("123456");
            System.out.println(hello);
        }
    }
}

 5. ServerBootstrap

package netty.rpc.provider;

import netty.rpc.netty.NettyServer;

/**
 * 启动一个服务的提供者，NettyServer
 */
public class ServerBootstrap {

    public static void main(String[] args) {
        NettyServer.start("127.0.0.1", 6666);
    }
}

　　可以看到上面的核心逻辑是，启动一个NettyServer、一个NettyClient。 NettyServer 用于启动Server服务器接收客户端发送的数据，NettyClient 实际也是一个任务，通过JDK的动态代理，在调用方法的时候，实际是用NettyClient 去向服务器端发送数据。 服务器端会根据接收到的数据进行判断，是否满足约定的协议，如果满足调用ServiceImpl 获取结果，然后输出给客户端。