1小時寫一個分佈式系統基礎框架

以前聽說在這個行業工作沒有2年經驗的，都不知道什麼是分佈式，我也快2年了，抱着好奇和時間之餘便看到了這篇文字，看了一下，講得很清楚，於是轉載了過來。以便於以後的閱讀，感悟分佈式架構的魅力、核心思想之所在。

互聯網時代，各種分佈式框架盛行，應用層面有各種變化，但是萬變不離其宗，RPC(remote procedure call)是最核心的部分，在其之上再開發服務註冊和發現，負載均衡，數據HA，調用鏈路記錄，等等功能。

分佈式系統非常複雜，今天只是管中窺豹，利用1小時搭建一個基礎系統。基礎系統組件可以歸納爲如下三個：

服務註冊中心，管理元數據（Registry）
服務提供方（Provider）
服務調用方（Consumer）

0. 流行系統分析

0.1 HBase

HBase是Apache Hadoop的數據庫，能夠對大型數據提供隨機、實時的讀寫訪問。極其複雜，我們不去深究，只看看它的基礎框架。

ZooKeeper管理元數據（Registry）
Data Node（Provider）
Client（Consumer）

0.2 Kafka

Kafka是由LinkedIn開發的一個分佈式的消息系統，使用Scala編寫，它以可水平擴展和高吞吐率而被廣泛使用。

ZooKeeper管理元數據（Registry）
Producer，Consumer（Consumer）
Broker（Provider）

0.3 Dubbo

Dubbo是阿里巴巴開發的一個分佈式服務框架，致力於提供高性能和透明化的RPC遠程服務調用方案，以及SOA服務治理方案。

1. 基礎框架開發

我們先不深究架構緣由，接下來我們按照如下框架開發。Netty應用在衆多分佈式系統中，我們也基於Netty開發，大家可以稍微修改即可應用在生產環境中。

1.0 整體框架

如下，分成4個模塊。接下來分別講解

common（提供基礎類定義）
registry（註冊中心）
client（服務調用方，Consumer）
server（服務提供方，Provider）

1.1 common

<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-all</artifactId>
    <version>4.0.36.Final</version>
</dependency>

1.1.1 Command.java

每一個調用都是一個命令

package com.parsecode.common;

import java.util.concurrent.atomic.AtomicLong;

public class Command {
    // 註冊服務端
    public final static int REGISTER_SERVER = 1;
    // 取消註冊
    public final static int UNREGISTER_SERVER = 2;
    // 調用方法
    public final static int INVOKE_REQUEST = 3;
    // 方法返回
    public final static int INVOKE_RESPONSE = 4;
    // 獲取服務列表
    public final static int GET_SERVER_LIST = 5;
    public final static int GET_SERVER_LIST_RESPONSE = 6;

    private static AtomicLong IDS = new AtomicLong(0);

    private int type;
    private long requestId;

    // 存放具體的方法調用信息、調用結果等
    private byte[] body;

    public Command(int type, byte[] body) {
        this.type = type;
        this.body = body;
        this.requestId = IDS.incrementAndGet();
    }

    // command 長度 = type(4) + requestId(8) + body.length
    public int length() {
        return 12 + (body == null ? 0 : body.length);
    }

    public int getType() {
        return type;
    }
    public void setType(int type) {
        this.type = type;
    }
    public byte[] getBody() { return body; }
    public void setBody(byte[] body) { this.body = body; }

    public long getRequestId() {
        return requestId;
    }

    public void setRequestId(long requestId) {
        this.requestId = requestId;
    }
}

1.1.2 Invocation.java

用來表示一個方法調用，包括了，調用是哪個接口，哪個方法，參數類型，參數值。會用JSON序列化成byte[]。

package com.parsecode.common;

import java.io.Serializable;

public class Invocation implements Serializable {
    private String interfaceName;
    private String methodName;
    private String[] parameterTypes;
    private Object[] arguments;

    public String getInterfaceName() {
        return interfaceName;
    }

    public void setInterfaceName(String interfaceName) {
        this.interfaceName = interfaceName;
    }

    public String getMethodName() {
        return methodName;
    }

    public void setMethodName(String methodName) {
        this.methodName = methodName;
    }

    public String[] getParameterTypes() {
        return parameterTypes;
    }

    public void setParameterTypes(String[] parameterTypes) {
        this.parameterTypes = parameterTypes;
    }

    public Object[] getArguments() {
        return arguments;
    }

    public void setArguments(Object[] arguments) {
        this.arguments = arguments;
    }
}

1.1.3 消息編解碼

也就是大家說的通信協議，簡單設計協議如下

消息解碼

package com.parsecode.common;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import java.nio.ByteBuffer;
public class NettyDecoder extends LengthFieldBasedFrameDecoder {

    public NettyDecoder() {
        super(65536, 0, 4, 0, 4);
    }

    @Override
    public Object decode(ChannelHandlerContext ctx, ByteBuf in) throws Exception {
        ByteBuf frame = null;
        try {
            frame = (ByteBuf) super.decode(ctx, in);
            if (null == frame) {
                return null;
            }

            ByteBuffer byteBuffer = frame.nioBuffer();
            int length = byteBuffer.limit();
            int type = byteBuffer.getInt();
            long requestId = byteBuffer.getLong();
            byte[] bodyData = null;
            if ((length - 12) > 0) {
                bodyData = new byte[length - 12];
                byteBuffer.get(bodyData);
            }
            Command cmd = new Command(type, bodyData);
            cmd.setRequestId(requestId);
            return cmd;
        } catch (Exception e) {
            ctx.channel().close().addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                    System.out.println("closeChannel");
                }
            });
        } finally {
            if (null != frame) {
                frame.release();
            }
        }
        return null;
    }
}

消息編碼

package com.parsecode.common;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;

public class NettyEncoder extends MessageToByteEncoder<Command> {
    @Override
    public void encode(ChannelHandlerContext ctx, Command cmd, ByteBuf out) {
        try {
            int length = cmd.length();
            out.writeInt(length);
            out.writeInt(cmd.getType());
            out.writeLong(cmd.getRequestId());
            out.writeBytes(cmd.getBody());
        } catch (Exception e) {
            ctx.channel().close();
        }
    }
}

1.2 registry

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <groupId>com.parsecode.framework</groupId>
        <artifactId>distributed-communication-all</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>

    <modelVersion>4.0.0</modelVersion>
    <packaging>jar</packaging>
    <artifactId>distributed-communication-registry</artifactId>
    <name>distributed-communication-registry ${project.version}</name>


    <dependencies>
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.0.36.Final</version>
        </dependency>
        <dependency>
            <groupId>com.parsecode.framework</groupId>
            <artifactId>distributed-communication-common</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-lang3</artifactId>
            <version>3.4</version>
        </dependency>
    </dependencies>
</project>

Registry.java

package com.parsecode.registry;

import com.parsecode.common.NettyDecoder;
import com.parsecode.common.NettyEncoder;
import com.parsecode.common.Command;
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.timeout.IdleStateHandler;
import org.apache.commons.lang3.StringUtils;

import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

public class Registry {
    private final ServerBootstrap serverBootstrap;
    private final EventLoopGroup eventLoopGroupWorker;
    private final EventLoopGroup eventLoopGroupBoss;

    // 存放對外提供的服務對象 <interface, servers>
    private final ConcurrentHashMap<String, List<String>> servers = new ConcurrentHashMap<String, List<String>>();

    public Registry() {
        this.serverBootstrap = new ServerBootstrap();

        this.eventLoopGroupBoss = new NioEventLoopGroup(1, new ThreadFactory() {
            private AtomicInteger threadIndex = new AtomicInteger(0);
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, String.format("NettyBoss_%d", this.threadIndex.incrementAndGet()));
            }
        });

        final int threadCount = Runtime.getRuntime().availableProcessors() * 2;
        this.eventLoopGroupWorker = new NioEventLoopGroup(threadCount, new ThreadFactory() {
            private AtomicInteger threadIndex = new AtomicInteger(0);
            private int threadTotal = threadCount;
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, String.format("NettyServerWorker_%d_%d", threadTotal, this.threadIndex.incrementAndGet()));
            }
        });
    }

    public void start() {
        serverBootstrap.group(eventLoopGroupBoss, eventLoopGroupWorker)
                .channel(NioServerSocketChannel.class)
                .option(ChannelOption.SO_BACKLOG, 1024) // 鏈接隊列個數
                .childOption(ChannelOption.TCP_NODELAY, true)
                .localAddress("127.0.0.1", 8200)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    public void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(
                                new NettyEncoder(),
                                new NettyDecoder(),
                                new IdleStateHandler(0, 0, 60), //空閒鏈路狀態處理
                                new NettyServerHandler());
                    }
                });

        try {
            serverBootstrap.bind().sync().addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture channelFuture) throws Exception {
                    System.out.println("registry 創建成功");
                }
            });
        } catch (InterruptedException e1) {
            throw new RuntimeException("serverBootstrap.bind().sync() InterruptedException", e1);
        }
    }

    class NettyServerHandler extends SimpleChannelInboundHandler<Command> {
        @Override
        protected void channelRead0(ChannelHandlerContext ctx, Command msg) throws Exception {
            processMessageReceived(ctx, msg);
        }
    }

    // 根據不同的命令，相應處理
    public void processMessageReceived(ChannelHandlerContext ctx, Command msg) {
        final Command cmd = msg;
        if (cmd != null) {
            switch (cmd.getType()) {
                case Command.GET_SERVER_LIST:
                    try {
                        String interfaceName = new String(msg.getBody(), "UTF-8");
                        List<String> ips = servers.get(interfaceName);
                        if (ips == null) {
                            ips = new ArrayList<String>();
                            servers.put(interfaceName, ips);
                        }
                        // 格式： ip:port,ip:port
                        String str = StringUtils.join(ips, ",");
                        byte[] body = String.valueOf(str).getBytes("UTF-8");
                        Command response = new Command(Command.GET_SERVER_LIST_RESPONSE, body);
                        response.setRequestId(msg.getRequestId());
                        ctx.channel().writeAndFlush(response);
                    } catch (Exception e) {}
                    break;
                case Command.REGISTER_SERVER:
                case Command.UNREGISTER_SERVER:
                    // 格式：interface,ip:port
                    try {
                        String str = new String(msg.getBody(), "UTF-8");
                        System.out.println("服務註冊：" + str);
                        String[] aStr = str.split(",");
                        List<String> ips = servers.get(aStr[0]);
                        if (ips == null) {
                            ips = new ArrayList<String>();
                            servers.put(aStr[0], ips);
                        }
                        if (msg.getType() == Command.REGISTER_SERVER && !ips.contains(aStr[1])) {
                            ips.add(aStr[1]);
                        } else {
                            ips.remove(aStr[1]);
                        }
                    } catch (Exception e){
                        System.out.println("error" + e.getMessage());
                    };
                    break;
                default:
                    break;
            }
        }
    }

    public static void main(String[] args) {
        Registry registry = new Registry();
        registry.start();
    }
}

1.3 server

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <groupId>com.parsecode.framework</groupId>
        <artifactId>distributed-communication-all</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>

    <modelVersion>4.0.0</modelVersion>
    <packaging>jar</packaging>
    <artifactId>distributed-communication-server</artifactId>
    <name>distributed-communication-server ${project.version}</name>


    <dependencies>
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.0.36.Final</version>
        </dependency>
        <dependency>
            <groupId>com.parsecode.framework</groupId>
            <artifactId>distributed-communication-common</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.12</version>
        </dependency>
    </dependencies>
</project>

ServiceProvder.java

package com.parsecode.server;

import com.alibaba.fastjson.JSON;
import com.parsecode.common.*;
import io.netty.bootstrap.Bootstrap;
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.channel.socket.nio.NioSocketChannel;
import io.netty.handler.timeout.IdleState;
import io.netty.handler.timeout.IdleStateEvent;
import io.netty.handler.timeout.IdleStateHandler;

import java.lang.reflect.Method;
import java.net.InetSocketAddress;
import java.util.*;
import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

public class ServiceProvider {
    // 提供服務
    private final ServerBootstrap serverBootstrap;
    // 鏈接註冊中心
    private final Bootstrap registry = new Bootstrap();

    private final EventLoopGroup eventLoopGroupWorker;
    private final EventLoopGroup eventLoopGroupBoss;
    private final EventLoopGroup eventLoopGroupRegistry;

    // 存放對外提供的服務對象 <interface, implement>
    private final Map<String, Object> services = new HashMap<String, Object>();

    // 向註冊中心，實時發送心跳
    private final Timer timer = new Timer("registry-heartbeat", true);

    public ServiceProvider() {
        this.serverBootstrap = new ServerBootstrap();

        this.eventLoopGroupBoss = new NioEventLoopGroup(1, new ThreadFactory() {
            private AtomicInteger threadIndex = new AtomicInteger(0);
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, String.format("NettyBoss_%d", this.threadIndex.incrementAndGet()));
            }
        });

        final int threadCount = Runtime.getRuntime().availableProcessors() * 2;
        this.eventLoopGroupWorker = new NioEventLoopGroup(threadCount, new ThreadFactory() {
            private AtomicInteger threadIndex = new AtomicInteger(0);
            private int threadTotal = threadCount;
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, String.format("NettyServerWorker_%d_%d", threadTotal, this.threadIndex.incrementAndGet()));
            }
        });

        eventLoopGroupRegistry = new NioEventLoopGroup(1, new ThreadFactory() {
            private AtomicInteger threadIndex = new AtomicInteger(0);
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, String.format("NettyClientRegistry_%d", this.threadIndex.incrementAndGet()));
            }
        });
    }

    public void addService(String interfaceName, Object service) {
        services.put(interfaceName, service);
    }

    public void start() {
        serverBootstrap.group(eventLoopGroupBoss, eventLoopGroupWorker)
                .channel(NioServerSocketChannel.class)
                .option(ChannelOption.SO_BACKLOG, 1024) // 鏈接隊列個數
                .option(ChannelOption.SO_REUSEADDR, true)
                .option(ChannelOption.SO_KEEPALIVE, false) //設置心跳參數 FALSE爲不啓用參數
                .childOption(ChannelOption.TCP_NODELAY, true)
                .localAddress(new InetSocketAddress(8080))
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    public void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(
                                new NettyEncoder(),
                                new NettyDecoder(),
                                new IdleStateHandler(0, 0, 60), //空閒鏈路狀態處理
                                new NettyServerHandler());
                    }
                });
        registry.group(this.eventLoopGroupRegistry)
                .channel(NioSocketChannel.class)
                .option(ChannelOption.TCP_NODELAY, true)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    public void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(
                                new NettyEncoder(),
                                new NettyDecoder(),
                                new IdleStateHandler(0, 0, 60),
                                new NettyServerHandler());
                    }
                });

        try {
            serverBootstrap.bind().sync();
        } catch (InterruptedException e1) {
            throw new RuntimeException("this.serverBootstrap.bind().sync() InterruptedException", e1);
        }

        // 向註冊中心，註冊自己
        timer.scheduleAtFixedRate(new TimerTask() {
            private volatile boolean registryOK = false;
            private volatile Channel channel;
            @Override
            public void run() {
                try {
                    while (!registryOK) {
                        // 註冊中心 port 8200
                        InetSocketAddress registryAddress = new InetSocketAddress("127.0.0.1", 8200);
                        ChannelFuture channelFuture = registry.connect(registryAddress);

                        channelFuture.syncUninterruptibly().addListener(new ChannelFutureListener() {
                            @Override
                            public void operationComplete(ChannelFuture channelFuture) throws Exception {
                                registryOK = true;
                                channel = channelFuture.channel();
                            }
                        });
                    }

                    if (registryOK && channel.isActive()) {
                        for (String key : services.keySet()) {
                            // 服務port和ip
                            byte[] body = (key + ",127.0.0.1:8080").getBytes("UTF-8");
                            Command cmd = new Command(Command.REGISTER_SERVER, body);
                            channel.writeAndFlush(cmd);
                            System.out.println("註冊服務 > " + channel.toString());
                        }
                    } else {
                        registryOK = false;
                        channel.close();
                    }
                } catch (Exception e) {
                    registryOK = false;
                    if (null != channel) {
                        channel.close();
                    }
                }
            }
        }, 10, 1000);
    }

    public void shutdown() {
        eventLoopGroupBoss.shutdownGracefully();
        eventLoopGroupWorker.shutdownGracefully();
    }

    class NettyServerHandler extends SimpleChannelInboundHandler<Command> {
        @Override
        protected void channelRead0(ChannelHandlerContext ctx, Command msg) throws Exception {
            final Command cmd = msg;
            switch (cmd.getType()) {
                case Command.INVOKE_REQUEST:
                    try {
                        Invocation invoke = JSON.parseObject(cmd.getBody(), Invocation.class);
                        // 找到服務
                        Object service = services.get(invoke.getInterfaceName());
                        Class cls = Class.forName(invoke.getInterfaceName());
                        List<Class> argsTypeList = new ArrayList<Class>(invoke.getParameterTypes().length);
                        for (String s : invoke.getParameterTypes()) {
                            argsTypeList.add(Class.forName(s));
                        }
                        Method method = cls.getMethod(invoke.getMethodName(), argsTypeList.toArray(new Class[argsTypeList.size()]));
                        Object result = method.invoke(service, invoke.getArguments());

                        Command response = new Command(Command.INVOKE_RESPONSE, JSON.toJSONBytes(result));
                        response.setRequestId(cmd.getRequestId());
                        ctx.channel().writeAndFlush(response);
                    } catch (Exception e) {}
                    break;
                default:
                    break;
            }
        }

        @Override
        public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
            if (evt instanceof IdleStateEvent) {
                IdleStateEvent evnet = (IdleStateEvent) evt;
                if (evnet.state().equals(IdleState.ALL_IDLE)) {
                    System.out.println("NETTY SERVER PIPELINE: IDLE exception");
                    ctx.channel().close();
                }
            }
            ctx.fireUserEventTriggered(evt);
        }
    }

    public static void main(String[] args) {
        ServiceProvider sp = new ServiceProvider();
        sp.addService(IService.class.getCanonicalName(), new ServiceImpl());
        sp.start();
    }
}

1.4 client

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <parent>
        <groupId>com.parsecode.framework</groupId>
        <artifactId>distributed-communication-all</artifactId>
        <version>0.0.1-SNAPSHOT</version>
    </parent>

    <modelVersion>4.0.0</modelVersion>
    <packaging>jar</packaging>
    <artifactId>distributed-communication-client</artifactId>
    <name>distributed-communication-client ${project.version}</name>


    <dependencies>
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.0.36.Final</version>
        </dependency>
        <dependency>
            <groupId>com.parsecode.framework</groupId>
            <artifactId>distributed-communication-common</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.12</version>
        </dependency>
    </dependencies>
</project>

ServiceConsumer.java

package com.parsecode.client;

import com.alibaba.fastjson.JSON;
import com.parsecode.common.*;
import io.netty.bootstrap.Bootstrap;
import io.netty.channel.*;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.timeout.IdleStateHandler;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.net.InetSocketAddress;
import java.util.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;

public class ServiceConsumer implements InvocationHandler {
    private final Bootstrap bootstrap = new Bootstrap();
    private final Bootstrap registry = new Bootstrap();

    // <ip:port, channel>，本例子只支持一個接口。生產環境需要支持多服務（interface）
    private final ConcurrentHashMap<String, Channel> channelTables = new ConcurrentHashMap<String, Channel>();
    // 存放調用響應
    private final ConcurrentHashMap<Long, Command> responses = new ConcurrentHashMap<Long, Command>();
    private final Timer timer = new Timer("registry-heartbeat", true);

    private final EventLoopGroup eventLoopGroupWorker;
    private final EventLoopGroup eventLoopGroupRegistry;

    // 遠端服務接口
    private Class interfaceClass;

    public ServiceConsumer(Class interfaceClass) {
        this.interfaceClass = interfaceClass;
        // 服務連接線程組
        eventLoopGroupWorker = new NioEventLoopGroup(1, new ThreadFactory() {
            private AtomicInteger threadIndex = new AtomicInteger(0);
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, String.format("NettyClientWorker_%d", this.threadIndex.incrementAndGet()));
            }
        });
        // 註冊中心連接線程組
        eventLoopGroupRegistry = new NioEventLoopGroup(1, new ThreadFactory() {
            private AtomicInteger threadIndex = new AtomicInteger(0);
            @Override
            public Thread newThread(Runnable r) {
                return new Thread(r, String.format("NettyClientRegistry_%d", this.threadIndex.incrementAndGet()));
            }
        });
    }

    /**
     * 這裏簡單的用代理就可以了。
     * 生產環境：需要用javassist，jdk等字節碼技術動態生產class
     */
    public <T> T getTarget() {
        final Class<?>[] interfaces = new Class[]{interfaceClass};
        return (T) Proxy.newProxyInstance(ServiceConsumer.class.getClassLoader(), interfaces, this);
    }

    public void start() {
        // 定義遠端服務連接參數
        bootstrap.group(this.eventLoopGroupWorker).channel(NioSocketChannel.class)//
                .option(ChannelOption.TCP_NODELAY, true)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    public void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(
                                new NettyEncoder(),
                                new NettyDecoder(),
                                new IdleStateHandler(0, 0, 6), //
                                new NettyClientHandler());
                    }
                });
        // 定義註冊中心連接參數
        registry.group(this.eventLoopGroupRegistry)
                .channel(NioSocketChannel.class)
                .option(ChannelOption.TCP_NODELAY, true)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    public void initChannel(SocketChannel ch) throws Exception {
                        ch.pipeline().addLast(
                                new NettyEncoder(),
                                new NettyDecoder(),
                                new IdleStateHandler(0, 0, 60),
                                new NettyClientHandler());
                    }
                });

        // 定期從註冊中心拉取服務端ip，port
        timer.scheduleAtFixedRate(new TimerTask() {
            volatile boolean registryOK = false;
            volatile Channel channel;

            @Override
            public void run() {
                try {
                    while (!registryOK) {
                        // 註冊中心 port 8200
                        ChannelFuture channelFuture = registry.connect(new InetSocketAddress("127.0.0.1", 8200));
                        channelFuture.syncUninterruptibly().addListener(new ChannelFutureListener() {
                            @Override
                            public void operationComplete(ChannelFuture channelFuture) throws Exception {
                                registryOK = true;
                                channel = channelFuture.channel();
                            }
                        });
                    }

                    if (registryOK && channel.isActive()) {
                        byte[] body = interfaceClass.getCanonicalName().getBytes("UTF-8");
                        Command cmd = new Command(Command.GET_SERVER_LIST, body);
                        channel.writeAndFlush(cmd);
                    } else {
                        channel.close();
                        registryOK = false;
                    }
                } catch (Exception e) {
                    registryOK = false;
                }
            }
        }, 10, 1000);
    }

    class NettyClientHandler extends SimpleChannelInboundHandler<Command> {
        @Override
        protected void channelRead0(ChannelHandlerContext ctx, Command msg) throws Exception {
            final Command cmd = msg;
            if (cmd != null) {
                switch (cmd.getType()) {
                    case Command.INVOKE_RESPONSE:
                        responses.put(msg.getRequestId(), msg);
                        break;
                    case Command.GET_SERVER_LIST_RESPONSE:
                        try {
                            String str = new String(msg.getBody(), "UTF-8");
                            String[] servers = str.split(",");
                            for (String ip : servers) {
                                System.out.println("服務提供者：" + ip);
                                String[] ipAndPort = ip.split(":");
                                // 已經連接到了服務端，跳過
                                if (channelTables.containsKey(ip)) {
                                    continue;
                                }
                                if (ipAndPort.length == 2) {
                                    Channel channel = bootstrap.connect(new InetSocketAddress(ipAndPort[0], Integer.parseInt(ipAndPort[1])))
                                            .sync().channel();
                                    channelTables.put(ip, channel);
                                }
                            }
                        }catch (Exception e){}
                        break;
                    default:
                        break;
                }
            }
        }// channelRead0
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        Invocation inv = new Invocation();
        inv.setInterfaceName(interfaceClass.getCanonicalName());
        inv.setMethodName(method.getName());
        inv.setArguments(args);

        String[] types = new String[method.getParameterTypes().length];
        int index = 0;
        for (Class type : method.getParameterTypes()) {
            types[index] = type.getCanonicalName();
            index++;
        }
        inv.setParameterTypes(types);

        Command cmd = new Command(Command.INVOKE_REQUEST, JSON.toJSONBytes(inv));
        // 如果服務端沒有就位，等待。這裏只是例子，生產環境需要用超時和線程池。
        while(channelTables.isEmpty()) {
            Thread.sleep(2);
        }
        for (String key : channelTables.keySet()) {
            channelTables.get(key).writeAndFlush(cmd);
            System.out.println("目標調用服務器：" + channelTables.get(key).toString());
        }

        // 等待服務端返回。生產環境需要用Future來控制，這裏爲了簡單。
        try {
            Thread.sleep(5);
        } catch (Exception e){}

        Command response = responses.get(cmd.getRequestId());
        if (response != null) {
            return JSON.parse(response.getBody());
        }
        return null;
    }

    public static void main(String[] args) throws Exception{
        ServiceConsumer sc = new ServiceConsumer(IService.class);
        sc.start();
        IService service = sc.getTarget();
        System.out.println("IService.hello(\"world\"): " + service.hello("world"));
    }
}

1.5 應用

1.5.1 定義服務

1.5.2 服務實現

調用效果

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