最近工作比较忙，但闲暇之余还是看了阿里的冯家春（fengjiachun）的github上的开源代码Jupiter，写的RPC框架让我感叹人外有人，废话不多说，下面的代码全部截取自Jupiter，写了一个比较完整的例子，供大家一起学习分享，再次对@Luca抱拳，Jupiter的Github地址：
https://github.com/fengjiachun/Jupiter
今天研究的是，心跳和重连，虽然这次是大神写的代码，但是万变不离其宗，我们先回顾一下Netty应用心跳和重连的整个过程：
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4s内没有write事件，则会触发userEventTriggered方法（上文介绍过）
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）加入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短线重连
以上描述的就是整个心跳和重连的整个过程，虽然很简单，上一篇blog也写了一个Demo,简单地做了一下上述功能
要写工业级的Netty心跳重连的代码，需要解决一下几个问题：
1）ChannelPipeline中的ChannelHandlers的维护，首次连接和重连都需要对ChannelHandlers进行管理
2）重连对象的管理，也就是bootstrap对象的管理
3）重连机制编写
完整的代码：https://github.com/BazingaLyn/netty-study/tree/master/src/main/java/com/lyncc/netty/idle
下面我们就看大神是如何解决这些问题的，首先先定义一个接口ChannelHandlerHolder，用来保管ChannelPipeline中的Handlers的
package com.lyncc.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();
}
我们再来编写我们熟悉的服务端的ServerBootstrap的编写：
HeartBeatServer.java
package com.lyncc.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<SocketChannel>() {
???????????????????????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();
???}
}
单独写一个AcceptorIdleStateTrigger，其实也是继承ChannelInboundHandlerAdapter，重写userEventTriggered方法，因为客户端是write，那么服务端自然是read，设置的状态就是IdleState.READER_IDLE，源码如下：
package com.lyncc.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);
???????}
???}
}
HeartBeatServerHandler就是一个很简单的自定义的Handler，不是重点：
package com.lyncc.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();
???}
}
接下来就是重点，我们需要写一个类，这个类可以去观察链路是否断了，如果断了，进行循环的断线重连操作，ConnectionWatchdog，顾名思义，链路检测狗，我们先看完整代码：
package com.lyncc.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<Channel>() {
???????????????@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");
???????????????}
???????????}
???????});
???????
???}
}
稍微分析一下：
1）继承了ChannelInboundHandlerAdapter，说明它也是Handler，也对，作为一个检测对象，肯定会放在链路中，否则怎么检测
2）实现了2个接口，TimeTask，ChannelHandlerHolder
①TimeTask，我们就要写run方法，这应该是一个定时任务，这个定时任务做的事情应该是重连的工作
②ChannelHandlerHolder的接口，这个接口我们刚才说过是维护的所有的Handlers，因为在重连的时候需要获取Handlers
3）bootstrap对象，重连的时候依旧需要这个对象
4）当链路断开的时候会触发channelInactive这个方法，也就说触发重连的导火索是从这边开始的
好了，我们这边再写次核心的HeartBeatsClient的代码：
package com.lyncc.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<Channel>() {
???????????????????????//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");
???}
}
也稍微说明一下：
1）创建了ConnectionWatchdog对象，自然要实现handlers方法
2）初始化好bootstrap对象
3）4秒内没有写操作，进行心跳触发，也就是IdleStateHandler这个方法
最后ConnectorIdleStateTrigger这个类
package com.lyncc.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);
???????}
???}
}
HeartBeatClientHandler.java(不是重点)
package com.lyncc.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);
???}
}
好了，到此为止，所有的代码都贴完了，我们做一个简单的测试，按照常理，如果不出任何状况的话，客户端4秒发送心跳，服务端5秒才验证是不会断连的，所以我们在启动之后，关闭服务端，然后再次重启服务端
首先启动服务端，控制台如下：
启动客户端，控制台如下：
客户端启动之后，服务端的控制台：
关闭服务端后，客户端控制台：
重启启动服务端：
---------------------
作者：BazingaLyncc
来源：CSDN
原文：https://blog.csdn.net/linuu/article/details/51509847
版权声明：本文为博主原创文章，转载请附上博文链接！
NETTY 心跳机制
原文地址：https://www.cnblogs.com/cfas/p/10113312.html