问题描述
我正在尝试使用Active MQ通过覆盖消息来实现延迟队列.
I am trying to implement delayed queue with overriding of messages using Active MQ.
每条消息计划以x的延迟发送(例如60秒)
Each message is scheduled to be delivered with delay of x (say 60 seconds)
在两次接收相同消息的过程中，它应该覆盖先前的消息.
In between if same message is received again it should override previous message.
因此，即使我在x秒内收到10条消息也要说.仅应处理一条消息.
So even if I receive 10 messages say in x seconds. Only one message should be processed.
有没有干净的方法来实现这一目标?
Is there clean way to accomplish this?
推荐答案
问题有两个部分需要分别解决:
The question has two parts that need to be addressed separately:
可以在ActiveMQ中延迟邮件吗?
是-请参见延迟和计划邮件传递.您需要在ActiveMQ配置中设置<broker ... schedulerSupport="true">，并设置JMS消息的AMQ_SCHEDULED_DELAY属性，该属性说明您希望消息延迟多长时间(在您的情况下为10000).
Yes - see Delay and Schedule Message Delivery. You need to set <broker ... schedulerSupport="true"> in your ActiveMQ config, as well as setting the AMQ_SCHEDULED_DELAY property of the JMS message saying how long you want the message to be delayed (10000 in your case).
有什么方法可以防止同一条消息被多次使用?
是的，但这是应用程序方面的问题，而不是ActiveMQ.它通常被称为重复数据删除或幂等消耗.如果只有一个使用者，最简单的方法是跟踪地图中收到的消息，并检查该地图是否收到消息.已经看到，丢弃.
Yes, but that's an application concern rather than an ActiveMQ one. It's often referred to as de-duplication or idempotent consumption. The simplest way if you only have one consumer is to keep track of messages received in a map, and check that map whether you receive a message. It it has been seen, discard.
对于更复杂的用例，如果您在不同的计算机上有多个使用者，或者希望该状态在应用程序重新启动后仍然存在，则需要保留一个在数据库中看到的消息表，并每次对其进行查询.
For more complex use cases where you have multiple consumers on different machines, or you want that state to survive application restart, you will need to keep a table of messages seen in a database, and query it each time.
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