Netty 学习2. 心跳与重连机制

心跳测试与重连的思路基本是如下6个步骤：

 1）客户端连接服务端；

 2）在客户端的的ChannelPipeline中加入一个比较特殊的IdleStateHandler，设置一下客户端的写空闲时间，例如5s；

 3）当客户端的所有ChannelHandler中5s内没有write事件，则会触发userEventTriggered方法（查看gitHub）；

 4）我们在客户端的userEventTriggered中对应的触发事件下发送一个心跳包给服务端，检测服务端是否还存活，防止服务端已经宕机，客户端还不知道；

 5）同样，服务端要对心跳包做出响应，其实给客户端最好的回复就是“不回复”，这样可以服务端的压力，假如有10w个空闲Idle的连接，那么服务端光发送心跳回复，则也是费事的事情，那么怎么才能告诉客户端它还活着呢，其实很简单，因为5s服务端都会收到来自客户端的心跳信息，那么如果10秒内收不到，服务端可以认为客户端挂了，可以close链路；

 6）假如服务端因为什么因素导致宕机的话，就会关闭所有的链路链接，所以作为客户端要做的事情就是断线重连。

1. 客户端

1.1 ChannelHandlerHolder

package com.ly.netty.idle;

import io.netty.channel.ChannelHandler;

/**
 * 
 * 客户端的ChannelHandler集合，由子类实现，这样做的好处：
 * 继承这个接口的所有子类可以很方便地获取ChannelPipeline中的Handlers
 * 获取到handlers之后方便ChannelPipeline中的handler的初始化和在重连的时候也能很方便
 * 地获取所有的handlers
 */
public interface ChannelHandlerHolder {

    ChannelHandler[] handlers();
}

1.2 ConnectionWatchdog

package com.ly.netty.idle;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.channel.ChannelInitializer;
import io.netty.util.Timeout;
import io.netty.util.Timer;
import io.netty.util.TimerTask;

import java.util.concurrent.TimeUnit;

/**
 * 
 * 重连检测狗，当发现当前的链路不稳定关闭之后，进行12次重连
 */
@Sharable
public abstract class ConnectionWatchdog extends ChannelInboundHandlerAdapter implements TimerTask ,ChannelHandlerHolder{
    
    
    
    private final Bootstrap bootstrap;
    private final Timer timer;
    private final int port;
    
    private final String host;

    private volatile boolean reconnect = true;
    private int attempts;
    
    
    public ConnectionWatchdog(Bootstrap bootstrap, Timer timer, int port,String host, boolean reconnect) {
        this.bootstrap = bootstrap;
        this.timer = timer;
        this.port = port;
        this.host = host;
        this.reconnect = reconnect;
    }
    
    /**
     * channel链路每次active的时候，将其连接的次数重新☞ 0
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        
        System.out.println("当前链路已经激活了，重连尝试次数重新置为0");
        
        attempts = 0;
        ctx.fireChannelActive();
    }
    
    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("链接关闭");
        if(reconnect){
            System.out.println("链接关闭，将进行重连");
            if (attempts < 12) {
                attempts++;
                //重连的间隔时间会越来越长
                int timeout = 2 << attempts;
                timer.newTimeout(this, timeout, TimeUnit.MILLISECONDS);
            }
        }
        ctx.fireChannelInactive();
    }
    

    public void run(Timeout timeout) throws Exception {
        
        ChannelFuture future;
        //bootstrap已经初始化好了，只需要将handler填入就可以了
        synchronized (bootstrap) {
            bootstrap.handler(new ChannelInitializer() {

                @Override
                protected void initChannel(Channel ch) throws Exception {
                    
                    ch.pipeline().addLast(handlers());
                }
            });
            future = bootstrap.connect(host,port);
        }
        //future对象
        future.addListener(new ChannelFutureListener() {

            public void operationComplete(ChannelFuture f) throws Exception {
                boolean succeed = f.isSuccess();

                //如果重连失败，则调用ChannelInactive方法，再次出发重连事件，一直尝试12次，如果失败则不再重连
                if (!succeed) {
                    System.out.println("重连失败");
                    f.channel().pipeline().fireChannelInactive();
                }else{
                    System.out.println("重连成功");
                }
            }
        });
        
    }

}

1.3 ConnectorIdleStateTrigger

package com.ly.netty.idle;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.handler.timeout.IdleState;
import io.netty.handler.timeout.IdleStateEvent;
import io.netty.util.CharsetUtil;

@Sharable
public class ConnectorIdleStateTrigger extends ChannelInboundHandlerAdapter {
    
    private static final ByteBuf HEARTBEAT_SEQUENCE = Unpooled.unreleasableBuffer(Unpooled.copiedBuffer("Heartbeat",
            CharsetUtil.UTF_8));

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        if (evt instanceof IdleStateEvent) {
            IdleState state = ((IdleStateEvent) evt).state();
            if (state == IdleState.WRITER_IDLE) {
                // write heartbeat to server
                ctx.writeAndFlush(HEARTBEAT_SEQUENCE.duplicate());
            }
        } else {
            super.userEventTriggered(ctx, evt);
        }
    }
}

1.4 HeartBeatClientHandler

package com.ly.netty.idle;

import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.ReferenceCountUtil;

import java.util.Date;

@Sharable
public class HeartBeatClientHandler extends ChannelInboundHandlerAdapter {

    
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("激活时间是："+new Date());
        System.out.println("HeartBeatClientHandler channelActive");
        ctx.fireChannelActive();
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("停止时间是："+new Date());
        System.out.println("HeartBeatClientHandler channelInactive");
    }


    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        String message = (String) msg;
        System.out.println(message);
        if (message.equals("Heartbeat")) {
            ctx.write("has read message from server");
            ctx.flush();
        }
        ReferenceCountUtil.release(msg);
    }
}

从InBound里读取的ByteBuf要手动释放，还有自己创建的ByteBuf要自己负责释放。这两处要调用这个release方法。

1.5 HeartBeatsClient

package com.ly.netty.idle;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.timeout.IdleStateHandler;
import io.netty.util.HashedWheelTimer;

import java.util.concurrent.TimeUnit;

public class HeartBeatsClient {
    
    protected final HashedWheelTimer timer = new HashedWheelTimer();
    
    private Bootstrap boot;
    
    private final ConnectorIdleStateTrigger idleStateTrigger = new ConnectorIdleStateTrigger();

    public void connect(int port, String host) throws Exception {
        
        EventLoopGroup group = new NioEventLoopGroup();  
        
        boot = new Bootstrap();
        boot.group(group).channel(NioSocketChannel.class).handler(new LoggingHandler(LogLevel.INFO));
            
        final ConnectionWatchdog watchdog = new ConnectionWatchdog(boot, timer, port,host, true) {

                public ChannelHandler[] handlers() {
                    return new ChannelHandler[] {
                            this,
                            new IdleStateHandler(0, 4, 0, TimeUnit.SECONDS),
                            idleStateTrigger,
                            new StringDecoder(),
                            new StringEncoder(),
                            new HeartBeatClientHandler()
                    };
                }
            };
            
            ChannelFuture future;
            //进行连接
            try {
                synchronized (boot) {
                    boot.handler(new ChannelInitializer() {

                        //初始化channel
                        @Override
                        protected void initChannel(Channel ch) throws Exception {
                            ch.pipeline().addLast(watchdog.handlers());
                        }
                    });

                    future = boot.connect(host,port);
                }

                // 以下代码在synchronized同步块外面是安全的
                future.sync();
            } catch (Throwable t) {
                throw new Exception("connects to  fails", t);
            }
    }

    /**
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {
        int port = 8080;
        if (args != null && args.length > 0) {
            try {
                port = Integer.valueOf(args[0]);
            } catch (NumberFormatException e) {
                // 采用默认值
            }
        }
        new HeartBeatsClient().connect(port, "127.0.0.1");
    }

}

2. 服务端

2.1 AcceptorIdleStateTrigger

package com.ly.netty.idle;

import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.handler.timeout.IdleState;
import io.netty.handler.timeout.IdleStateEvent;


@ChannelHandler.Sharable
public class AcceptorIdleStateTrigger extends ChannelInboundHandlerAdapter {

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
        if (evt instanceof IdleStateEvent) {
            IdleState state = ((IdleStateEvent) evt).state();
            if (state == IdleState.READER_IDLE) {
                throw new Exception("idle exception");
            }
        } else {
            super.userEventTriggered(ctx, evt);
        }
    }
}

2.2 HeartBeatServer

package com.ly.netty.idle;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
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.string.StringDecoder;
import io.netty.handler.codec.string.StringEncoder;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.timeout.IdleStateHandler;

import java.net.InetSocketAddress;
import java.util.concurrent.TimeUnit;

public class HeartBeatServer {
    
    private final AcceptorIdleStateTrigger idleStateTrigger = new AcceptorIdleStateTrigger();
    
    private int port;

    public HeartBeatServer(int port) {
        this.port = port;
    }

    public void start() {
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap sbs = new ServerBootstrap().group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class).handler(new LoggingHandler(LogLevel.INFO))
                    .localAddress(new InetSocketAddress(port)).childHandler(new ChannelInitializer() {
                        protected void initChannel(SocketChannel ch) throws Exception {
                            ch.pipeline().addLast(new IdleStateHandler(5, 0, 0, TimeUnit.SECONDS));
                            ch.pipeline().addLast(idleStateTrigger);
                            ch.pipeline().addLast("decoder", new StringDecoder());
                            ch.pipeline().addLast("encoder", new StringEncoder());
                            ch.pipeline().addLast(new HeartBeatServerHandler());
                        };

                    }).option(ChannelOption.SO_BACKLOG, 128).childOption(ChannelOption.SO_KEEPALIVE, true);
            // 绑定端口，开始接收进来的连接
            ChannelFuture future = sbs.bind(port).sync();

            System.out.println("Server start listen at " + port);
            future.channel().closeFuture().sync();
        } catch (Exception e) {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }

    public static void main(String[] args) throws Exception {
        int port;
        if (args.length > 0) {
            port = Integer.parseInt(args[0]);
        } else {
            port = 8080;
        }
        new HeartBeatServer(port).start();
    }

}

2.3HeartBeatServerHandler

package com.ly.netty.idle;

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

public class HeartBeatServerHandler extends ChannelInboundHandlerAdapter {


    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        System.out.println("server channelRead..");
        System.out.println(ctx.channel().remoteAddress() + "->Server :" + msg.toString());
    }

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

 //当读取不到消息后，Netty触发ChannelReadCompleted().
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        ctx.flush();
    }

}

启动测试---

1、先启动服务端、再启动客户端

2、关闭服务端，重启

3、会自动重连

我的Github项目，欢迎大家指导！Watch！Star！Fork! Thanks！
GitHub-Netty-demo-server
GitHub-Netty-demo-client