1、什么是消息确认ACK。

  答:如果在处理消息的过程中,消费者的服务器在处理消息的时候出现异常,那么可能这条正在处理的消息就没有完成消息消费,数据就会丢失。为了确保数据不会丢失,RabbitMQ支持消息确定-ACK。

2、ACK的消息确认机制。

  答:ACK机制是消费者从RabbitMQ收到消息并处理完成后,反馈给RabbitMQ,RabbitMQ收到反馈后才将此消息从队列中删除。

    如果一个消费者在处理消息出现了网络不稳定、服务器异常等现象,那么就不会有ACK反馈,RabbitMQ会认为这个消息没有正常消费,会将消息重新放入队列中。
    如果在集群的情况下,RabbitMQ会立即将这个消息推送给这个在线的其他消费者。这种机制保证了在消费者服务端故障的时候,不丢失任何消息和任务。
    消息永远不会从RabbitMQ中删除,只有当消费者正确发送ACK反馈,RabbitMQ确认收到后,消息才会从RabbitMQ服务器的数据中删除。
    消息的ACK确认机制默认是打开的。

3、ACK机制的开发注意事项。

  答:如果忘记了ACK,那么后果很严重。当Consumer退出时候,Message会一直重新分发。然后RabbitMQ会占用越来越多的内容,由于RabbitMQ会长时间运行,因此这个"内存泄漏"是致命的。

4、结合项目实例进行,理解一下ACK机制。之前写过RabbitMQ的交换器Exchange之direct(发布与订阅 完全匹配),这里借助这个进行消息持久化测试。生产者的代码不发生改变。控制层的触发生产者生产消息,这里只生产一条消息。方便观察现象。

 package com.example.bie.controller;

 import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody; import com.example.bie.provider.RabbitMqLogErrorProduce;
import com.example.bie.provider.RabbitMqLogInfoProduce; /**
*
* @author biehl
*
*/
@Controller
public class RabbitmqController { @Autowired
private RabbitMqLogInfoProduce rabbitMqLogInfoProduce; @Autowired
private RabbitMqLogErrorProduce rabbitMqLogErrorProduce; @RequestMapping(value = "/logInfo")
@ResponseBody
public String rabbitmqSendLogInfoMessage() {
String msg = "生产者===>生者的LogInfo消息message: ";
for (int i = ; i < ; i++) {
rabbitMqLogInfoProduce.producer(msg + i);
}
return "生产===> LogInfo消息message ===> success!!!";
} @RequestMapping(value = "/logError")
@ResponseBody
public String rabbitmqSendLogErrorMessage() {
String msg = "生产者===>生者的LogError消息message: ";
for (int i = ; i < ; i++) {
rabbitMqLogErrorProduce.producer(msg + i);
}
return "生产===> LogError消息message ===> success!!!";
} }

消费者消费消息,打印输出后面手动抛出运行时异常,观察现象。

 package com.example.bie.consumer;

 import org.springframework.amqp.core.ExchangeTypes;
import org.springframework.amqp.rabbit.annotation.Exchange;
import org.springframework.amqp.rabbit.annotation.Queue;
import org.springframework.amqp.rabbit.annotation.QueueBinding;
import org.springframework.amqp.rabbit.annotation.RabbitHandler;
import org.springframework.amqp.rabbit.annotation.RabbitListener;
import org.springframework.stereotype.Component; /**
*
* @author biehl
*
* 消息接收者
*
* 1、@RabbitListener bindings:绑定队列
*
* 2、@QueueBinding
* value:绑定队列的名称、exchange:配置交换器、key:路由键routing-key绑定队列和交换器
*
* 3、@Queue value:配置队列名称、autoDelete:是否是一个可删除的临时队列
*
* 4、@Exchange value:为交换器起个名称、type:指定具体的交换器类型
*
*
*/
@Component
@RabbitListener(bindings = @QueueBinding( value = @Queue(value = "${rabbitmq.config.queue.error}", autoDelete = "true"), exchange = @Exchange(value = "${rabbitmq.config.exchange}", type = ExchangeTypes.DIRECT), key = "${rabbitmq.config.queue.error.routing.key}"))
public class LogErrorConsumer { /**
* 接收消息的方法,采用消息队列监听机制.
*
* @RabbitHandler意思是将注解@RabbitListener配置到类上面
*
* @RabbitHandler是指定这个方法可以进行消息的接收并且消费.
*
* @param msg
*/
@RabbitHandler
public void consumer(String msg) {
// 打印消息
System.out.println("ERROR消费者===>消费<===消息message: " + msg);
throw new RuntimeException();
} }

观察现象,如下所示:

在RabbitMQ的浏览器界面,可以看到一条消息未被进行ACK的消息确认机制,这条消息被锁定Unacked,所以一直在控制台进行报错。

控制台效果如下所示,一直进行消息的发送,因为消费方一直没有返回ACK确认,RabbitMQ认为消息未进行正常的消费,会将消息再次放入到队列中,再次让你消费,但是还是没有返回ACK确认,依次循环,形成了死循环。

如何解决问题呢,如果消息发送的时候,程序出现异常,后果很严重的,会导致内存泄漏的,所以在程序处理中可以进行异常捕获,保证消费者的程序正常执行,这里不进行介绍了。第二种方式可以使用RabbitMQ的ack确认机制。开启重试,然后重试次数,默认为3次。这里设置为5次。

 # 给当前项目起名称.
spring.application.name=rabbitmq-ack-direct-consumer # 配置端口号
server.port= # 配置rabbitmq的参数.
# rabbitmq服务器的ip地址.
spring.rabbitmq.host=192.168.110.133
# rabbitmq的端口号5672,区别于浏览器访问界面的15672端口号.
spring.rabbitmq.port=
# rabbitmq的账号.
spring.rabbitmq.username=guest
# rabbitmq的密码.
spring.rabbitmq.password=guest # 设置交换器的名称,方便修改.
# 路由键是将交换器和队列进行绑定的,队列通过路由键绑定到交换器.
rabbitmq.config.exchange=log.exchange.direct # info级别的队列名称.
rabbitmq.config.queue.info=log.info.queue
# info的路由键.
rabbitmq.config.queue.info.routing.key=log.info.routing.key # error级别的队列名称.
rabbitmq.config.queue.error=log.error.queue
# error的路由键.
rabbitmq.config.queue.error.routing.key=log.error.routing.key # 开启重试
spring.rabbitmq.listener.simple.retry.enabled=true
# 重试次数,默认为3次
spring.rabbitmq.listener.simple.retry.max-attempts=

效果如下所示:

可以看到控制台尝试了5次以后就不再进行重试了。

RabbitMQ的界面可以看到,开始的效果和上面的一致,但是5次尝试以后,就变成了0条。RabbitMQ将这条消息丢弃了。

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9D0oATBJpCMGnA8V/VIOB1/OgD8bf8Agibx8fPHWf8AoWT/AOlUFfsHoH/IPP8A13m/9GvVof6/8Dn9Kq6B/wAg8/8AXeb/ANGvQBo18U/t2aRPZfHj9nXxNptg97qdtrVxAIYHVJLgAQyJEGPHO2QDJx8x9a+1q+QP24vF9p4M+Lf7Ot/eRzTwReI7mRobaJpZW/dxp8iKCWOZBwBnmgZ0P7MX/C7L7xZ4l1P4g+EdE8K2ep3IvJLgTNNezjbtigVVfaqxrtG4+h+Ukkjw/wD4KG/tFeEk8a6b8PNZSXU9K0SH+2b/AEu3YhdSveBbWcjr/q4wC0jnkn5QMHmvWfix8Xfi9qfjjwLo/hSGw8GaV4n1UWlsmp25m1WW2jXzLm6aMnbCirhQpBbLDJXOK8j8df8ABNLXPjR+0V438V+JfEceieFb+++02wtFE91cqyjIwSFjAIIyd3070BszA/Zc+EXjf4s/sw6/4k8M/EvU/hy95q99fwaTo8CRWCMpBKgriRVyCOGwABwcc/RH/BOj40+JPjT8B5LzxVPJf6ppWoyWH9oS/fuUCK6sx7sN+Cfavk39mP4FfGr4j/CbxLpfw9+Jkfh/wLJq17pEumakjF/K4DOjKrY3BiCFI5z65r9E/gD8FdL+APwv0jwZpMhuYrJS8926bGuZmOZJCBnGT0GTgYGTQD3PR6zte/5B3/baH/0ataNZ2vf8g7/ttD/6NWgQ+T/kJr/uf1NfyykYNf1Nyf8AISXjjZ/U1bHAxmgD+VkDJoxg0o4PT86/qk70AOHav5WK/qmziv5WSCKACgda/qnoOaADOK/lYIwa/qlxmlHAAzQB/KzQOtGKUAigD+qbOK/lYIxTvamnrQB/VRRRRQAUUUUAFFFFADS2DSgkgHFBGa/lYJyaAFHJ607ryTTAcV/VPjFAH8rfbtX9UY5HT86/layQaQnJoA/qnPT1poPOMU4jNfys5oA/qmHNGKB0paAP5WAOetf1SA9v1NOIyKMACgBp69K/lbPB6/lSZwaCcmgD9FP+CKHHx98cD/qWT/6VQV+wegf8g8/9d5v/AEa9W8fv/wDgJ/pVTQP+Qef+u83/AKNegDRr5j/bP+AHiL4v6h8MPEfhPbLrfg/X47z7PJMI1eB5IWkbJ4yphQ/TdxX05ScE0Afnz4g+E/xY/ab/AGzbnVNYXWPBHgTwbcyWdjqNo72ss8WcsIH4LGXALMOAvHav0BijEKBQSQOBk5qUKBnA61Fdyrb20srcKilj9AKA3PlD/gmnGy/ArXGOQG8T6gR/30tfWnSvkv8A4Jl3H2v9na7uArKk3iC/kUN6Fx09a+taBhWdr3/IO/7bQ/8Ao1a0azte/wCQd/22h/8ARq0CPx8/4LZY/wCF++Bv+xZGf/Aqevzsx71/U0/Opr/uf1NXaAExX8rWc1/VNX8q/TFAH9UwGRzzSgY7V/KxRQB/VOTgU3JPH604jNfysk0AB4pM0daKAP6pyOOlfytds8c1/VKRkYNGMCgBhP15r+VwjnrR61/VN0oAWiiigAooooAKKKKACiiigD+VcDJr+qfI69qCCQRmk24oAXIoByMiv5Ws9vfrX9UoPHWgD+VgDNf1Tg5r+VgdaceBjFAH9U1FfysDntRn2oAQDJr+qcHNBBIIzSBcGgBSQOtAORSMuT17V/K1kelAH9UPW4/4Cap6Af8AiXkf9N5v/Rr1+DH/AATQ+Pmk/AT9puwu9fuorDQdfs5NFu7ybASDzHR43ZiQEUSRpuY9AT25r917e4fwzNcQTW88tjJK00U8EZk2FjllZRyPmJIOCMHtigDoqKzR4gsz/wA/H/gLL/8AE0f8JBZ/9PP/AICS/wDxNAGlWL4y1B9L8K6tcxWlxfyx20hS2tI98srbThVXIySferH/AAkFn/08/wDgJL/8TSHXrM/8/P8A4Cy//E0AeY/slfCe9+CvwE8M+F9TCLqsUb3F4iHISaVi7LnvjdjPtXsNZi69ZqMYuP8AwEl/+Jpf+Egs/wDp5/8AASX/AOJoA0qzteP/ABLv+20P/o1KQ+ILP0uf/ASX/wCJrPnuZPEk8FvBBNDYxyrLLNOhjLlDuCqp56gEnGMCgDVf/kJr/uf1NfyyV/UnZ3aX188sZ3xKNqsOh9xX8tpHNACAZr+qcEV/KwOtO6cUAf1S7h60A5FN25Oc/hX8reR6UAJ1r+qfvQQSOtfytE5HSgD+qaiv5WfwFJn2oA/qmJwK/lYIxSg4PSgncKAEAzX9U4ORX8rIO0UFgT0oA/qnooooAKKKKACiiigAooooAQkgE4pA2c1/KyDg1/VPjGaAP5WhnnHrSEcnmjOM1/VMBgUAfysgc9a/qkU5NO61/KwaAP6pW64/lX8rR6/4UA4oJyaAP6qKKKKAGs2D07V/K1getf1TEA9aAMCgD+VocHrX9PV1Jq+k5Fm0c0Y+7HOpIHp0Oa6sjI5pCi4+6PyoA/G8f8FsfiiAf+KG8H/983X/AMepD/wWz+KQOP8AhBfCH/fN1/8AHq/OvPWv6o/s8X/PNP8AvkUAcB/wmPin/oH2P/fL/wDxVflef+C2fxTGf+KF8Ifldf8Ax6vzqzX9UYt4h/yyT/vkUAfjkP8Agtn8UiM/8IL4Q/75uv8A49X6nnxh4pBx9gsf++X/APiq7/yIh/yzUfQUfZ4h/wAs0/75FAH44f8AD7P4pHj/AIQXwh/3zdf/AB6v1Yjk13XQEvJI4LduGjt1IDD3JJOOfWu38iL/AJ5p/wB8iv5WzQB/UzplitnAqADFXsY7V/KxRQAoHPWv6pAee/1pxGRRgAUAN3EHpX8rZA9aPWv6pulAC1/KwK/qnr+VfpigD+qXnOOee9fytHr/AIUZoJyaAP6p8ewpD/nFfys0DrQA7HfNNIwa/qmxnFfysk5oA/qoooooAKKKKACiiigBCQOtAORTWHOfbpX8rZ69KAEoHWv6p8+4oP1FAAOlLSDijNAATgZNGcihulfytZ7YoAT1r+qbrTSK/lbJ56UAIBmv6ps5zX8rI604nAx6UANxk0EYNf1S4561/K0Tk0AFHWjFKBg80AJigjBr+qXBODntX8rROTQAUDrRilHWgD+qYdKWv5WcZ6DNJ+FACda/qnz1obp1r+VokGgBuMmgjBr+qXHPWv5WicmgD+qcnAyaMignjrX8rWe3v1oA/ql64r+Viv6punvX8rJBFAH9U/Sv5WDSg89K/qkUYNAH8rQr+qfrTW5PWv5WyeelACUDrX9U9BzQADtX8rFf1TgYr+VigD+qiiiigAooooAKKKKAGseeaF6Dj86UjNfysE5NABmjNFFACgZHWgjB60gOK/qnAwKAA80hGBX8rNA60AO79aTHvX9Uw6UtAH8rAHPWv6pFyTTutfysGgD+qYkg4r+VkjBoBxQTk0Af1TkcdK/laxxnjrX9UpGRg0YwKAG7uQMV/K0Rg0ZwaCcmgD+qY8AnFJnNfytA4Nf1T4HTtQB/K2ADX9UY6dKXFfysdaAP6pz09aaOTinEZr+VgmgD+qYkg4r+VkjBoBxQTk0AL+NL1PJzX9U1FADCfUUq9Bx+dLgdO1fysE5NABQSTRRQA5ema/qkHI6fnX8rIJFBOTQB/VPRX8rFFAH9UxYg9K/laIHrSCv6p+lAC0UUUAFFFFABRRRQAhIHWgHIpGXJ69q/layPSgD+qeiv5WPwo/CgD+qeiv5WPwo/CgD+qeiv5WPwpeh5GKAP6pcjr2r+VgjBr+qbbmlAIAGaAAnFfys4r+qY9PSmgc5zQA7OK/lYIwa/qlK570o4AGaAP5Wa/qnPev5WME1/VN1oA/lZxk0EYNf1TbTnOa/lZJyaAP6pycCv5WcUA4PSlLZ7UAf1S5wKAcjIr+VrPGMfjX9Uq9KAP5WKB1r+qfPuKD9RQAZxX8rBGDX9UpFOXoOc0ABOK/lZIr+qY9PSmgdT+lAH8rXSilIyaSgD+qcnAyaMihulfytZGPp3oA/ql64r+Viv6plr+VmgD+qcnAyaM5FBGRX8rQIxigBp60Up60mKAP6qKKKKACiiigAooooATvX8rFf1T96/lYoA/qnPA6UgOTjFKRmv5WCaAP6p8ewox7Cv5WKKAP6p8A1/Kzmv6p6/lX9KAP6px0paQdKWgBrdDxn6V/K2RgZpoODQSTQAoGR1oIwetIDiv6pwMCgBG6Hj8qFPPFfysg4Nf1TgYoAO9fysV/VP3r+VigD+qfFB4paQ9KAExmlHFfysHrRQAv40D61/VPSHpQB/K0Bx/Q1/VIvQcY+tfytZINITk0Af1Tt06V/K2QBimdK/qnxQAgGa/lZJzX9U/TFfysUAf1Tnmk21/KzRQB/VMSQcV/KyRg0A4oJyaAP6pySB0r+VoqB3/Om9K/qnx1oAbnnp19acOR0r+VnNf1TAYoAWiiigAooooAKKKKAE71/KxX9U/ev5WKAP6qK/lX7V/VOTiv5WSKAEooxRigD+qiv5V/Sv6qK/lX9KAP6p84xX8rBGDX9UxXOKUAgAZoAWv5V/Sv6p8gV/KzigD+qbOMV/KwRg1/VMRn8KBwAM0AfysgZNf1Tg5pDyCM0AbTQApIHWgHIpCMmv5Wsj0oAQDJr+qfI69qQ8gjNJtx3oAdmv5WOlPBAzX9Ui9OtAH8rFf1TnvX8rFf1TkZoA/lZ9a/qm601gc1/K2evSgBK/qnPev5WK/qnPegD+Vg9aKD1ooAAMmv6pwc0EEgjNIBtNACkgdaAcimtye9fytnr0oA/qnr+Vfriv6p81/K1jFADcUEYNf1SnPX9K/lbI56flQB/VPRRRQAUUUUAFFFFACd6/lYr+qfvX8rFAH9U55oAxX8rFFAH9U+PYUY9hX8rFFAH9U5JAzjNfyskYwfekBwaMkmgD+qcdKWkHSloA/lXzS7iaSigAzRmiigAzSjmko6UAf1S5I96/lbIHrSZr+qfpQB/KwOT1p2Mc579KaDiv6pwBQA0mnL0HGKMDp2r+VgnJo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作者:别先生

博客园:https://www.cnblogs.com/biehongli/

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