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:
重连成功~