RabbitMQ消息监听异常问题探究

亦凉 2022-06-08 00:30 325阅读 0赞

### **问题场景** ###

在使用Spring RabbitMQ做消息监听时，如果监听程序处理异常了，且未对异常进行捕获，会一直重复接收消息，然后一直抛异常。为了更好的描述问题，下面写个简单的例子。

通过访问null对象来引发空指针异常，消息监听处理程序代码清单:

package amqp;
    
    import org.springframework.amqp.core.Message;
    import org.springframework.amqp.core.MessageListener;
    import org.springframework.stereotype.Component;
    
    
    @Component
    public class FooMessageListener implements MessageListener { 
    
        @Override
        public void onMessage(Message message) { 
            String messageBody = new String(message.getBody());
            System.out.println(" [x] Received '" + messageBody + "'");
            String nullStr = null;
            nullStr.toString();
        }
    }

往消息监听队列发送一条消息，控制台不停打印异常日志：

18:55:32.816 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Retrieving delivery for Consumer: tags=[{amq.ctag-s5myKVHHeP4FbTGIH0hyeA=directQueue}], channel=Cached Rabbit Channel: AMQChannel(amqp://it@192.168.48.59:5672/,1), conn: Proxy@fd85a26 Shared Rabbit Connection: SimpleConnection@68887242 [delegate=amqp://it@192.168.48.59:5672/, localPort= 49412], acknowledgeMode=AUTO local queue size=0
    18:55:32.979 [pool-1-thread-10] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Storing delivery for Consumer: tags=[{amq.ctag-s5myKVHHeP4FbTGIH0hyeA=directQueue}], channel=Cached Rabbit Channel: AMQChannel(amqp://it@192.168.48.59:5672/,1), conn: Proxy@fd85a26 Shared Rabbit Connection: SimpleConnection@68887242 [delegate=amqp://it@192.168.48.59:5672/, localPort= 49412], acknowledgeMode=AUTO local queue size=0
    18:55:32.979 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Received message: (Body:'Hello, world!' MessageProperties [headers={}, timestamp=null, messageId=null, userId=null, receivedUserId=null, appId=null, clusterId=null, type=null, correlationId=null, correlationIdString=null, replyTo=null, contentType=text/plain, contentEncoding=UTF-8, contentLength=0, deliveryMode=null, receivedDeliveryMode=PERSISTENT, expiration=null, priority=0, redelivered=false, receivedExchange=, receivedRoutingKey=directQueue, receivedDelay=null, deliveryTag=1, messageCount=0, consumerTag=amq.ctag-s5myKVHHeP4FbTGIH0hyeA, consumerQueue=directQueue])
     [x] Received 'Hello, world!'
    18:55:38.191 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] WARN org.springframework.amqp.rabbit.listener.ConditionalRejectingErrorHandler - Execution of Rabbit message listener failed.
    org.springframework.amqp.rabbit.listener.exception.ListenerExecutionFailedException: Listener threw exception
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.wrapToListenerExecutionFailedExceptionIfNeeded(AbstractMessageListenerContainer.java:870)
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:780)
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.invokeListener(AbstractMessageListenerContainer.java:700)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.access$001(SimpleMessageListenerContainer.java:95)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$1.invokeListener(SimpleMessageListenerContainer.java:187)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.invokeListener(SimpleMessageListenerContainer.java:1187)
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.executeListener(AbstractMessageListenerContainer.java:681)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.doReceiveAndExecute(SimpleMessageListenerContainer.java:1165)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.receiveAndExecute(SimpleMessageListenerContainer.java:1149)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.access$1100(SimpleMessageListenerContainer.java:95)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$AsyncMessageProcessingConsumer.run(SimpleMessageListenerContainer.java:1312)
    	at java.lang.Thread.run(Thread.java:745)
    Caused by: java.lang.NullPointerException: null
    	at amqp.FooMessageListener.onMessage(FooMessageListener.java:16)
    	at org.springframework.amqp.rabbit.listener.adapter.MessageListenerAdapter.onMessage(MessageListenerAdapter.java:282)
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:777)
    	... 10 common frames omitted
    18:55:38.192 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Rejecting messages (requeue=true)
    18:55:38.193 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Retrieving delivery for Consumer: tags=[{amq.ctag-s5myKVHHeP4FbTGIH0hyeA=directQueue}], channel=Cached Rabbit Channel: AMQChannel(amqp://it@192.168.48.59:5672/,1), conn: Proxy@fd85a26 Shared Rabbit Connection: SimpleConnection@68887242 [delegate=amqp://it@192.168.48.59:5672/, localPort= 49412], acknowledgeMode=AUTO local queue size=0
    18:55:38.194 [pool-1-thread-3] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Storing delivery for Consumer: tags=[{amq.ctag-s5myKVHHeP4FbTGIH0hyeA=directQueue}], channel=Cached Rabbit Channel: AMQChannel(amqp://it@192.168.48.59:5672/,1), conn: Proxy@fd85a26 Shared Rabbit Connection: SimpleConnection@68887242 [delegate=amqp://it@192.168.48.59:5672/, localPort= 49412], acknowledgeMode=AUTO local queue size=0
    18:55:38.195 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Received message: (Body:'Hello, world!' MessageProperties [headers={}, timestamp=null, messageId=null, userId=null, receivedUserId=null, appId=null, clusterId=null, type=null, correlationId=null, correlationIdString=null, replyTo=null, contentType=text/plain, contentEncoding=UTF-8, contentLength=0, deliveryMode=null, receivedDeliveryMode=PERSISTENT, expiration=null, priority=0, redelivered=true, receivedExchange=, receivedRoutingKey=directQueue, receivedDelay=null, deliveryTag=2, messageCount=0, consumerTag=amq.ctag-s5myKVHHeP4FbTGIH0hyeA, consumerQueue=directQueue])
     [x] Received 'Hello, world!'
    18:55:55.226 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] WARN org.springframework.amqp.rabbit.listener.ConditionalRejectingErrorHandler - Execution of Rabbit message listener failed.
    org.springframework.amqp.rabbit.listener.exception.ListenerExecutionFailedException: Listener threw exception
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.wrapToListenerExecutionFailedExceptionIfNeeded(AbstractMessageListenerContainer.java:870)
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:780)
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.invokeListener(AbstractMessageListenerContainer.java:700)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.access$001(SimpleMessageListenerContainer.java:95)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$1.invokeListener(SimpleMessageListenerContainer.java:187)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.invokeListener(SimpleMessageListenerContainer.java:1187)
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.executeListener(AbstractMessageListenerContainer.java:681)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.doReceiveAndExecute(SimpleMessageListenerContainer.java:1165)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.receiveAndExecute(SimpleMessageListenerContainer.java:1149)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer.access$1100(SimpleMessageListenerContainer.java:95)
    	at org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer$AsyncMessageProcessingConsumer.run(SimpleMessageListenerContainer.java:1312)
    	at java.lang.Thread.run(Thread.java:745)
    Caused by: java.lang.NullPointerException: null
    	at amqp.FooMessageListener.onMessage(FooMessageListener.java:16)
    	at org.springframework.amqp.rabbit.listener.adapter.MessageListenerAdapter.onMessage(MessageListenerAdapter.java:282)
    	at org.springframework.amqp.rabbit.listener.AbstractMessageListenerContainer.doInvokeListener(AbstractMessageListenerContainer.java:777)
    	... 10 common frames omitted
    18:55:55.226 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Rejecting messages (requeue=true)
    18:55:55.227 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Retrieving delivery for Consumer: tags=[{amq.ctag-s5myKVHHeP4FbTGIH0hyeA=directQueue}], channel=Cached Rabbit Channel: AMQChannel(amqp://it@192.168.48.59:5672/,1), conn: Proxy@fd85a26 Shared Rabbit Connection: SimpleConnection@68887242 [delegate=amqp://it@192.168.48.59:5672/, localPort= 49412], acknowledgeMode=AUTO local queue size=0
    18:55:55.229 [pool-1-thread-4] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Storing delivery for Consumer: tags=[{amq.ctag-s5myKVHHeP4FbTGIH0hyeA=directQueue}], channel=Cached Rabbit Channel: AMQChannel(amqp://it@192.168.48.59:5672/,1), conn: Proxy@fd85a26 Shared Rabbit Connection: SimpleConnection@68887242 [delegate=amqp://it@192.168.48.59:5672/, localPort= 49412], acknowledgeMode=AUTO local queue size=0
    18:55:55.230 [org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer#0-2] DEBUG org.springframework.amqp.rabbit.listener.BlockingQueueConsumer - Received message: (Body:'Hello, world!' MessageProperties [headers={}, timestamp=null, messageId=null, userId=null, receivedUserId=null, appId=null, clusterId=null, type=null, correlationId=null, correlationIdString=null, replyTo=null, contentType=text/plain, contentEncoding=UTF-8, contentLength=0, deliveryMode=null, receivedDeliveryMode=PERSISTENT, expiration=null, priority=0, redelivered=true, receivedExchange=, receivedRoutingKey=directQueue, receivedDelay=null, deliveryTag=3, messageCount=0, consumerTag=amq.ctag-s5myKVHHeP4FbTGIH0hyeA, consumerQueue=directQueue])

**问题来了：为什么异常时会一直重复接收这条消息？**

### **抓包验证** ###

消息监听程序异常的过程到底发生了什么？为了一探究竟，笔者使用Wireshark抓包工具来查看消息处理过程。

首先，修改下监听程序，收到字符串exception时产生异常

@Override
     public void onMessage(Message message) { 
         String messageBody = new String(message.getBody());
         System.out.println(" [x] Received '" + messageBody + "'");
         if(messageBody.equals("exception")){ 
             String nullStr = null;
             nullStr.toString();
         }
     }

#### **1.监听程序正常处理情况** ####

启动监听程序，Wireshark抓包情况：

![启动监听程序][31cc633b815a60c9aba3891cafbfeaa9.png]

我们主要关注最后一列，这一列展示了请求的AMQP协议方法信息，AMQP协议方法包含类名+方法名+参数，这一列主要展示了类名和方法名，点击对应行可以查看参数信息。比如上图：

*  Connection.Start：请求服务端开始建立连接
 *  Channel.Open：请求服务端建立信道
 *  Queue.Declare：声明队列
 *  Basic.Consume：开始一个消费者，请求指定队列的消息

AMQP协议方法更详细介绍可以查看[官网][Link 1]

然后，通过客户端发送一条消息

RabbitTemplate template = ctx.getBean(RabbitTemplate.class);
    template.convertAndSend("ok");

抓包：

![ack][]

分析：

*  Basic.Publish： 客户端发送Basic.Publish方法请求，将消息发布到exchange，rabbitmq server会根据路由规则转发到队列中
 *  Basic.Deliver： 服务端发送Basic.Deliver方法请求，投递消息到监听队列的客户端消费者
 *  Basic.Ack： 客户端发送Basic.Ack方法请求，告知rabbimq server,消息已接收处理

#### **2.监听程序异常处理情况** ####

通过客户端发送exception字符串，制造异常

RabbitTemplate template = ctx.getBean(RabbitTemplate.class);
    template.convertAndSend("exception");

抓包：

![reject][]

分析：

*  Basic.Reject： 客户端发送Basic.Reject方法请求，表示无法处理消息，拒绝消息，此时的requeue参数为true，将消息返回原来的队列
 *  Basic.Deliver： 服务端调用Basic.Deliver方法，和第一次Basic.Deliver方法不同的是，此时的redeliver参数为true，表示重新投递消息到监听队列的消费者

然后这两步会一直重复下去。对于Basic.Reject方法，可以设置requeue参数为false，这样消息无法处理的时候就不会重新入队了，他会根据异常类型选择直接丢弃或加入[dead-letter-exchange][]中。Spring RabbitMQ配置：

<rabbit:listener-container connection-factory="connectionFactory" requeue-rejected="false">
        <rabbit:listener ref="fooMessageListener" queue-names="directQueue" />
    </rabbit:listener-container>

### **结论** ###

RabbitMQ消息监听程序异常时，消费者会向rabbitmq server发送Basic.Reject，表示消息拒绝接受，由于Spring默认requeue-rejected配置为true，消息会重新入队，然后rabbitmq server重新投递，造成了程序一直异常的情况。所以说了这么多，我们通过rabbitmq监听消息的时候，程序一定要添加try…catch语句!!!当然你也可以根据实际情况，选择设置requeue-rejected为false来丢弃消息。

### **参考** ###

\[1\] [AMQP协议方法][AMQP]  
\[2\] [Wireshark抓包教程][Wireshark]  
\[3\] http://blog.csdn.net/u013256816/article/details/55515234  
\[4\] http://fengchj.com/?p=2234  
\[5\] https://yemengying.com/2017/01/30/how-does-rabbitmq-handle-exception/

[31cc633b815a60c9aba3891cafbfeaa9.png]: /images/20220608/8c0fefafec03482987bb81da9bc13ee7.png
[Link 1]: https://www.rabbitmq.com/amqp-0-9-1-reference.html
[ack]: /images/20220608/cdb218335d0446eca935f51567db4147.png
[reject]: /images/20220608/45d02c09e72b4377b26aaf3fcca16459.png
[dead-letter-exchange]: https://www.rabbitmq.com/dlx.html
[AMQP]: https://www.rabbitmq.com/amqp-0-9-1-quickref.html
[Wireshark]: http://www.cnblogs.com/TankXiao/archive/2012/10/10/2711777.html