來源：www.jianshu.com/p/1a28e48edd92

心跳機(jī)制

何為心跳

所謂心跳, 即在 TCP 長(zhǎng)連接中, 客戶端和服務(wù)器之間定期發(fā)送的一種特殊的數(shù)據(jù)包, 通知對(duì)方自己還在線, 以確保 TCP 連接的有效性.

注：心跳包還有另一個(gè)作用，經(jīng)常被忽略，即：一個(gè)連接如果長(zhǎng)時(shí)間不用，防火墻或者路由器就會(huì)斷開該連接。

如何實(shí)現(xiàn)

核心Handler —— IdleStateHandler

在 Netty 中, 實(shí)現(xiàn)心跳機(jī)制的關(guān)鍵是 IdleStateHandler, 那么這個(gè) Handler 如何使用呢? 先看下它的構(gòu)造器：

public?IdleStateHandler(int?readerIdleTimeSeconds,?int?writerIdleTimeSeconds,?int?allIdleTimeSeconds)?{this((long)readerIdleTimeSeconds,?(long)writerIdleTimeSeconds,?(long)allIdleTimeSeconds,?TimeUnit.SECONDS); }

這里解釋下三個(gè)參數(shù)的含義：

• readerIdleTimeSeconds: 讀超時(shí). 即當(dāng)在指定的時(shí)間間隔內(nèi)沒有從 Channel 讀取到數(shù)據(jù)時(shí), 會(huì)觸發(fā)一個(gè) READER_IDLE 的 IdleStateEvent 事件.

• writerIdleTimeSeconds: 寫超時(shí). 即當(dāng)在指定的時(shí)間間隔內(nèi)沒有數(shù)據(jù)寫入到 Channel 時(shí), 會(huì)觸發(fā)一個(gè) WRITER_IDLE 的 IdleStateEvent 事件.

• allIdleTimeSeconds: 讀/寫超時(shí). 即當(dāng)在指定的時(shí)間間隔內(nèi)沒有讀或?qū)懖僮鲿r(shí), 會(huì)觸發(fā)一個(gè) ALL_IDLE 的 IdleStateEvent 事件.

注：這三個(gè)參數(shù)默認(rèn)的時(shí)間單位是秒。若需要指定其他時(shí)間單位，可以使用另一個(gè)構(gòu)造方法：IdleStateHandler(boolean observeOutput, long readerIdleTime, long writerIdleTime, long allIdleTime, TimeUnit unit)

在看下面的實(shí)現(xiàn)之前，建議先了解一下IdleStateHandler的實(shí)現(xiàn)原理。

下面直接上代碼，需要注意的地方，會(huì)在代碼中通過注釋進(jìn)行說明。

使用IdleStateHandler實(shí)現(xiàn)心跳

下面將使用IdleStateHandler來實(shí)現(xiàn)心跳，Client端連接到Server端后，會(huì)循環(huán)執(zhí)行一個(gè)任務(wù)：隨機(jī)等待幾秒，然后ping一下Server端，即發(fā)送一個(gè)心跳包。當(dāng)?shù)却臅r(shí)間超過規(guī)定時(shí)間，將會(huì)發(fā)送失敗，以為Server端在此之前已經(jīng)主動(dòng)斷開連接了。代碼如下：

Client端

ClientIdleStateTrigger —— 心跳觸發(fā)器

類ClientIdleStateTrigger也是一個(gè)Handler，只是重寫了userEventTriggered方法，用于捕獲IdleState.WRITER_IDLE事件（未在指定時(shí)間內(nèi)向服務(wù)器發(fā)送數(shù)據(jù)），然后向Server端發(fā)送一個(gè)心跳包。

/***?<p>*??用于捕獲{@link?IdleState#WRITER_IDLE}事件（未在指定時(shí)間內(nèi)向服務(wù)器發(fā)送數(shù)據(jù)），然后向<code>Server</code>端發(fā)送一個(gè)心跳包。*?</p>*/ public?class?ClientIdleStateTrigger?extends?ChannelInboundHandlerAdapter?{public?static?final?String?HEART_BEAT?=?"heart?beat!";@Overridepublic?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?serverctx.writeAndFlush(HEART_BEAT);}}?else?{super.userEventTriggered(ctx,?evt);}}}

Pinger —— 心跳發(fā)射器

/***?<p>客戶端連接到服務(wù)器端后，會(huì)循環(huán)執(zhí)行一個(gè)任務(wù)：隨機(jī)等待幾秒，然后ping一下Server端，即發(fā)送一個(gè)心跳包。</p>*/ public?class?Pinger?extends?ChannelInboundHandlerAdapter?{private?Random?random?=?new?Random();private?int?baseRandom?=?8;private?Channel?channel;@Overridepublic?void?channelActive(ChannelHandlerContext?ctx)?throws?Exception?{super.channelActive(ctx);this.channel?=?ctx.channel();ping(ctx.channel());}private?void?ping(Channel?channel)?{int?second?=?Math.max(1,?random.nextInt(baseRandom));System.out.println("next?heart?beat?will?send?after?"?+?second?+?"s.");ScheduledFuture<?>?future?=?channel.eventLoop().schedule(new?Runnable()?{@Overridepublic?void?run()?{if?(channel.isActive())?{System.out.println("sending?heart?beat?to?the?server...");channel.writeAndFlush(ClientIdleStateTrigger.HEART_BEAT);}?else?{System.err.println("The?connection?had?broken,?cancel?the?task?that?will?send?a?heart?beat.");channel.closeFuture();throw?new?RuntimeException();}}},?second,?TimeUnit.SECONDS);future.addListener(new?GenericFutureListener()?{@Overridepublic?void?operationComplete(Future?future)?throws?Exception?{if?(future.isSuccess())?{ping(channel);}}});}@Overridepublic?void?exceptionCaught(ChannelHandlerContext?ctx,?Throwable?cause)?throws?Exception?{//?當(dāng)Channel已經(jīng)斷開的情況下,?仍然發(fā)送數(shù)據(jù),?會(huì)拋異常,?該方法會(huì)被調(diào)用.cause.printStackTrace();ctx.close();} }

ClientHandlersInitializer —— 客戶端處理器集合的初始化類

public?class?ClientHandlersInitializer?extends?ChannelInitializer<SocketChannel>?{private?ReconnectHandler?reconnectHandler;private?EchoHandler?echoHandler;public?ClientHandlersInitializer(TcpClient?tcpClient)?{Assert.notNull(tcpClient,?"TcpClient?can?not?be?null.");this.reconnectHandler?=?new?ReconnectHandler(tcpClient);this.echoHandler?=?new?EchoHandler();}@Overrideprotected?void?initChannel(SocketChannel?ch)?throws?Exception?{ChannelPipeline?pipeline?=?ch.pipeline();pipeline.addLast(new?LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,?0,?4,?0,?4));pipeline.addLast(new?LengthFieldPrepender(4));pipeline.addLast(new?StringDecoder(CharsetUtil.UTF_8));pipeline.addLast(new?StringEncoder(CharsetUtil.UTF_8));pipeline.addLast(new?Pinger());} }

注：上面的Handler集合，除了Pinger，其他都是編解碼器和解決粘包，可以忽略。

TcpClient —— TCP連接的客戶端

public?class?TcpClient?{private?String?host;private?int?port;private?Bootstrap?bootstrap;/**?將<code>Channel</code>保存起來,?可用于在其他非handler的地方發(fā)送數(shù)據(jù)?*/private?Channel?channel;public?TcpClient(String?host,?int?port)?{this(host,?port,?new?ExponentialBackOffRetry(1000,?Integer.MAX_VALUE,?60?*?1000));}public?TcpClient(String?host,?int?port,?RetryPolicy?retryPolicy)?{this.host?=?host;this.port?=?port;init();}/***?向遠(yuǎn)程TCP服務(wù)器請(qǐng)求連接*/public?void?connect()?{synchronized?(bootstrap)?{ChannelFuture?future?=?bootstrap.connect(host,?port);this.channel?=?future.channel();}}private?void?init()?{EventLoopGroup?group?=?new?NioEventLoopGroup();//?bootstrap?可重用,?只需在TcpClient實(shí)例化的時(shí)候初始化即可.bootstrap?=?new?Bootstrap();bootstrap.group(group).channel(NioSocketChannel.class).handler(new?ClientHandlersInitializer(TcpClient.this));}public?static?void?main(String[]?args)?{TcpClient?tcpClient?=?new?TcpClient("localhost",?2222);tcpClient.connect();}}

Server端

ServerIdleStateTrigger —— 斷連觸發(fā)器

/***?<p>在規(guī)定時(shí)間內(nèi)未收到客戶端的任何數(shù)據(jù)包,?將主動(dòng)斷開該連接</p>*/ public?class?ServerIdleStateTrigger?extends?ChannelInboundHandlerAdapter?{@Overridepublic?void?userEventTriggered(ChannelHandlerContext?ctx,?Object?evt)?throws?Exception?{if?(evt?instanceof?IdleStateEvent)?{IdleState?state?=?((IdleStateEvent)?evt).state();if?(state?==?IdleState.READER_IDLE)?{//?在規(guī)定時(shí)間內(nèi)沒有收到客戶端的上行數(shù)據(jù),?主動(dòng)斷開連接ctx.disconnect();}}?else?{super.userEventTriggered(ctx,?evt);}} }

ServerBizHandler —— 服務(wù)器端的業(yè)務(wù)處理器

/***?<p>收到來自客戶端的數(shù)據(jù)包后,?直接在控制臺(tái)打印出來.</p>*/ @ChannelHandler.Sharable public?class?ServerBizHandler?extends?SimpleChannelInboundHandler<String>?{private?final?String?REC_HEART_BEAT?=?"I?had?received?the?heart?beat!";@Overrideprotected?void?channelRead0(ChannelHandlerContext?ctx,?String?data)?throws?Exception?{try?{System.out.println("receive?data:?"?+?data); //????????????ctx.writeAndFlush(REC_HEART_BEAT);}?catch?(Exception?e)?{e.printStackTrace();}}@Overridepublic?void?channelActive(ChannelHandlerContext?ctx)?throws?Exception?{System.out.println("Established?connection?with?the?remote?client.");//?do?somethingctx.fireChannelActive();}@Overridepublic?void?channelInactive(ChannelHandlerContext?ctx)?throws?Exception?{System.out.println("Disconnected?with?the?remote?client.");//?do?somethingctx.fireChannelInactive();}@Overridepublic?void?exceptionCaught(ChannelHandlerContext?ctx,?Throwable?cause)?throws?Exception?{cause.printStackTrace();ctx.close();} }

ServerHandlerInitializer —— 服務(wù)器端處理器集合的初始化類

/***?<p>用于初始化服務(wù)器端涉及到的所有<code>Handler</code></p>*/ public?class?ServerHandlerInitializer?extends?ChannelInitializer<SocketChannel>?{protected?void?initChannel(SocketChannel?ch)?throws?Exception?{ch.pipeline().addLast("idleStateHandler",?new?IdleStateHandler(5,?0,?0));ch.pipeline().addLast("idleStateTrigger",?new?ServerIdleStateTrigger());ch.pipeline().addLast("frameDecoder",?new?LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,?0,?4,?0,?4));ch.pipeline().addLast("frameEncoder",?new?LengthFieldPrepender(4));ch.pipeline().addLast("decoder",?new?StringDecoder());ch.pipeline().addLast("encoder",?new?StringEncoder());ch.pipeline().addLast("bizHandler",?new?ServerBizHandler());}}

注：new IdleStateHandler(5, 0, 0)該handler代表如果在5秒內(nèi)沒有收到來自客戶端的任何數(shù)據(jù)包（包括但不限于心跳包），將會(huì)主動(dòng)斷開與該客戶端的連接。

TcpServer —— 服務(wù)器端

public?class?TcpServer?{private?int?port;private?ServerHandlerInitializer?serverHandlerInitializer;public?TcpServer(int?port)?{this.port?=?port;this.serverHandlerInitializer?=?new?ServerHandlerInitializer();}public?void?start()?{EventLoopGroup?bossGroup?=?new?NioEventLoopGroup(1);EventLoopGroup?workerGroup?=?new?NioEventLoopGroup();try?{ServerBootstrap?bootstrap?=?new?ServerBootstrap();bootstrap.group(bossGroup,?workerGroup).channel(NioServerSocketChannel.class).childHandler(this.serverHandlerInitializer);//?綁定端口，開始接收進(jìn)來的連接ChannelFuture?future?=?bootstrap.bind(port).sync();System.out.println("Server?start?listen?at?"?+?port);future.channel().closeFuture().sync();}?catch?(Exception?e)?{bossGroup.shutdownGracefully();workerGroup.shutdownGracefully();e.printStackTrace();}}public?static?void?main(String[]?args)?throws?Exception?{int?port?=?2222;new?TcpServer(port).start();} }

至此，所有代碼已經(jīng)編寫完畢。

測(cè)試

首先啟動(dòng)客戶端，再啟動(dòng)服務(wù)器端。啟動(dòng)完成后，在客戶端的控制臺(tái)上，可以看到打印如下類似日志：

客戶端控制臺(tái)輸出的日志

在服務(wù)器端可以看到控制臺(tái)輸出了類似如下的日志：

服務(wù)器端控制臺(tái)輸出的日志

可以看到，客戶端在發(fā)送4個(gè)心跳包后，第5個(gè)包因?yàn)榈却龝r(shí)間較長(zhǎng)，等到真正發(fā)送的時(shí)候，發(fā)現(xiàn)連接已斷開了；而服務(wù)器端收到客戶端的4個(gè)心跳數(shù)據(jù)包后，遲遲等不到下一個(gè)數(shù)據(jù)包，所以果斷斷開該連接。

在測(cè)試過程中，有可能會(huì)出現(xiàn)如下情況：

異常情況

出現(xiàn)這種情況的原因是：在連接已斷開的情況下，仍然向服務(wù)器端發(fā)送心跳包。雖然在發(fā)送心跳包之前會(huì)使用判斷連接是否可用，但也有可能上一刻判斷結(jié)果為可用，但下一刻發(fā)送數(shù)據(jù)包之前，連接就斷了。

目前尚未找到優(yōu)雅處理這種情況的方案，各位看官如果有好的解決方案，還望不吝賜教。拜謝！！！

斷線重連

斷線重連這里就不過多介紹，相信各位都知道是怎么回事。這里只說大致思路，然后直接上代碼。

實(shí)現(xiàn)思路

客戶端在監(jiān)測(cè)到與服務(wù)器端的連接斷開后，或者一開始就無法連接的情況下，使用指定的重連策略進(jìn)行重連操作，直到重新建立連接或重試次數(shù)耗盡。

對(duì)于如何監(jiān)測(cè)連接是否斷開，則是通過重寫ChannelInboundHandler#channelInactive來實(shí)現(xiàn)，但連接不可用，該方法會(huì)被觸發(fā)，所以只需要在該方法做好重連工作即可。

代碼實(shí)現(xiàn)

注：以下代碼都是在上面心跳機(jī)制的基礎(chǔ)上修改/添加的。

因?yàn)閿嗑€重連是客戶端的工作，所以只需對(duì)客戶端代碼進(jìn)行修改。

重試策略

RetryPolicy —— 重試策略接口

public?interface?RetryPolicy?{/***?Called?when?an?operation?has?failed?for?some?reason.?This?method?should?return*?true?to?make?another?attempt.**?@param?retryCount?the?number?of?times?retried?so?far?(0?the?first?time)*?@return?true/false*/boolean?allowRetry(int?retryCount);/***?get?sleep?time?in?ms?of?current?retry?count.**?@param?retryCount?current?retry?count*?@return?the?time?to?sleep*/long?getSleepTimeMs(int?retryCount); }

ExponentialBackOffRetry —— 重連策略的默認(rèn)實(shí)現(xiàn)

/***?<p>Retry?policy?that?retries?a?set?number?of?times?with?increasing?sleep?time?between?retries</p>*/ public?class?ExponentialBackOffRetry?implements?RetryPolicy?{private?static?final?int?MAX_RETRIES_LIMIT?=?29;private?static?final?int?DEFAULT_MAX_SLEEP_MS?=?Integer.MAX_VALUE;private?final?Random?random?=?new?Random();private?final?long?baseSleepTimeMs;private?final?int?maxRetries;private?final?int?maxSleepMs;public?ExponentialBackOffRetry(int?baseSleepTimeMs,?int?maxRetries)?{this(baseSleepTimeMs,?maxRetries,?DEFAULT_MAX_SLEEP_MS);}public?ExponentialBackOffRetry(int?baseSleepTimeMs,?int?maxRetries,?int?maxSleepMs)?{this.maxRetries?=?maxRetries;this.baseSleepTimeMs?=?baseSleepTimeMs;this.maxSleepMs?=?maxSleepMs;}@Overridepublic?boolean?allowRetry(int?retryCount)?{if?(retryCount?<?maxRetries)?{return?true;}return?false;}@Overridepublic?long?getSleepTimeMs(int?retryCount)?{if?(retryCount?<?0)?{throw?new?IllegalArgumentException("retries?count?must?greater?than?0.");}if?(retryCount?>?MAX_RETRIES_LIMIT)?{System.out.println(String.format("maxRetries?too?large?(%d).?Pinning?to?%d",?maxRetries,?MAX_RETRIES_LIMIT));retryCount?=?MAX_RETRIES_LIMIT;}long?sleepMs?=?baseSleepTimeMs?*?Math.max(1,?random.nextInt(1?<<?retryCount));if?(sleepMs?>?maxSleepMs)?{System.out.println(String.format("Sleep?extension?too?large?(%d).?Pinning?to?%d",?sleepMs,?maxSleepMs));sleepMs?=?maxSleepMs;}return?sleepMs;} }

ReconnectHandler—— 重連處理器

@ChannelHandler.Sharable public?class?ReconnectHandler?extends?ChannelInboundHandlerAdapter?{private?int?retries?=?0;private?RetryPolicy?retryPolicy;private?TcpClient?tcpClient;public?ReconnectHandler(TcpClient?tcpClient)?{this.tcpClient?=?tcpClient;}@Overridepublic?void?channelActive(ChannelHandlerContext?ctx)?throws?Exception?{System.out.println("Successfully?established?a?connection?to?the?server.");retries?=?0;ctx.fireChannelActive();}@Overridepublic?void?channelInactive(ChannelHandlerContext?ctx)?throws?Exception?{if?(retries?==?0)?{System.err.println("Lost?the?TCP?connection?with?the?server.");ctx.close();}boolean?allowRetry?=?getRetryPolicy().allowRetry(retries);if?(allowRetry)?{long?sleepTimeMs?=?getRetryPolicy().getSleepTimeMs(retries);System.out.println(String.format("Try?to?reconnect?to?the?server?after?%dms.?Retry?count:?%d.",?sleepTimeMs,?++retries));final?EventLoop?eventLoop?=?ctx.channel().eventLoop();eventLoop.schedule(()?->?{System.out.println("Reconnecting?...");tcpClient.connect();},?sleepTimeMs,?TimeUnit.MILLISECONDS);}ctx.fireChannelInactive();}private?RetryPolicy?getRetryPolicy()?{if?(this.retryPolicy?==?null)?{this.retryPolicy?=?tcpClient.getRetryPolicy();}return?this.retryPolicy;} }

ClientHandlersInitializer

在之前的基礎(chǔ)上，添加了重連處理器ReconnectHandler。

public?class?ClientHandlersInitializer?extends?ChannelInitializer<SocketChannel>?{private?ReconnectHandler?reconnectHandler;private?EchoHandler?echoHandler;public?ClientHandlersInitializer(TcpClient?tcpClient)?{Assert.notNull(tcpClient,?"TcpClient?can?not?be?null.");this.reconnectHandler?=?new?ReconnectHandler(tcpClient);this.echoHandler?=?new?EchoHandler();}@Overrideprotected?void?initChannel(SocketChannel?ch)?throws?Exception?{ChannelPipeline?pipeline?=?ch.pipeline();pipeline.addLast(this.reconnectHandler);pipeline.addLast(new?LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,?0,?4,?0,?4));pipeline.addLast(new?LengthFieldPrepender(4));pipeline.addLast(new?StringDecoder(CharsetUtil.UTF_8));pipeline.addLast(new?StringEncoder(CharsetUtil.UTF_8));pipeline.addLast(new?Pinger());} }

TcpClient

在之前的基礎(chǔ)上添加重連、重連策略的支持。

public?class?TcpClient?{private?String?host;private?int?port;private?Bootstrap?bootstrap;/**?重連策略?*/private?RetryPolicy?retryPolicy;/**?將<code>Channel</code>保存起來,?可用于在其他非handler的地方發(fā)送數(shù)據(jù)?*/private?Channel?channel;public?TcpClient(String?host,?int?port)?{this(host,?port,?new?ExponentialBackOffRetry(1000,?Integer.MAX_VALUE,?60?*?1000));}public?TcpClient(String?host,?int?port,?RetryPolicy?retryPolicy)?{this.host?=?host;this.port?=?port;this.retryPolicy?=?retryPolicy;init();}/***?向遠(yuǎn)程TCP服務(wù)器請(qǐng)求連接*/public?void?connect()?{synchronized?(bootstrap)?{ChannelFuture?future?=?bootstrap.connect(host,?port);future.addListener(getConnectionListener());this.channel?=?future.channel();}}public?RetryPolicy?getRetryPolicy()?{return?retryPolicy;}private?void?init()?{EventLoopGroup?group?=?new?NioEventLoopGroup();//?bootstrap?可重用,?只需在TcpClient實(shí)例化的時(shí)候初始化即可.bootstrap?=?new?Bootstrap();bootstrap.group(group).channel(NioSocketChannel.class).handler(new?ClientHandlersInitializer(TcpClient.this));}private?ChannelFutureListener?getConnectionListener()?{return?new?ChannelFutureListener()?{@Overridepublic?void?operationComplete(ChannelFuture?future)?throws?Exception?{if?(!future.isSuccess())?{future.channel().pipeline().fireChannelInactive();}}};}public?static?void?main(String[]?args)?{TcpClient?tcpClient?=?new?TcpClient("localhost",?2222);tcpClient.connect();}}

測(cè)試

在測(cè)試之前，為了避開 Connection reset by peer 異常，可以稍微修改Pinger的ping()方法，添加if (second == 5)的條件判斷。如下：

private?void?ping(Channel?channel)?{int?second?=?Math.max(1,?random.nextInt(baseRandom));if?(second?==?5)?{second?=?6;}System.out.println("next?heart?beat?will?send?after?"?+?second?+?"s.");ScheduledFuture<?>?future?=?channel.eventLoop().schedule(new?Runnable()?{@Overridepublic?void?run()?{if?(channel.isActive())?{System.out.println("sending?heart?beat?to?the?server...");channel.writeAndFlush(ClientIdleStateTrigger.HEART_BEAT);}?else?{System.err.println("The?connection?had?broken,?cancel?the?task?that?will?send?a?heart?beat.");channel.closeFuture();throw?new?RuntimeException();}}},?second,?TimeUnit.SECONDS);future.addListener(new?GenericFutureListener()?{@Overridepublic?void?operationComplete(Future?future)?throws?Exception?{if?(future.isSuccess())?{ping(channel);}}});}

啟動(dòng)客戶端

先只啟動(dòng)客戶端，觀察控制臺(tái)輸出，可以看到類似如下日志：

斷線重連測(cè)試——客戶端控制臺(tái)輸出

可以看到，當(dāng)客戶端發(fā)現(xiàn)無法連接到服務(wù)器端，所以一直嘗試重連。隨著重試次數(shù)增加，重試時(shí)間間隔越大，但又不想無限增大下去，所以需要定一個(gè)閾值，比如60s。如上圖所示，當(dāng)下一次重試時(shí)間超過60s時(shí)，會(huì)打印Sleep extension too large(*). Pinning to 60000，單位為ms。出現(xiàn)這句話的意思是，計(jì)算出來的時(shí)間超過閾值（60s），所以把真正睡眠的時(shí)間重置為閾值（60s）。

啟動(dòng)服務(wù)器端

接著啟動(dòng)服務(wù)器端，然后繼續(xù)觀察客戶端控制臺(tái)輸出。

圖片

斷線重連測(cè)試——服務(wù)器端啟動(dòng)后客戶端控制臺(tái)輸出

可以看到，在第9次重試失敗后，第10次重試之前，啟動(dòng)的服務(wù)器，所以第10次重連的結(jié)果為，即成功連接到服務(wù)器。接下來因?yàn)檫€是不定時(shí)服務(wù)器，所以出現(xiàn)斷線重連、斷線重連的循環(huán)。

擴(kuò)展

在不同環(huán)境，可能會(huì)有不同的重連需求。有不同的重連需求的，只需自己實(shí)現(xiàn)RetryPolicy接口，然后在創(chuàng)建TcpClient的時(shí)候覆蓋默認(rèn)的重連策略即可。

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