在应用程序启动和关闭时管理JMS消息容器

Question

Currently, we have four JMS listener containers that are started during the application start. They all connect through Apache ZooKeeper and are manually started. This becomes problematic when a connection to ZooKeeper cannot be established. The (Wicket) application cannot start, even though it is not necessary for the JMS listeners be active to use the application. They simply need to listen to messages in the background, save them and a cron job will process them in batches.

Goals :

1. Allow the application to start and not be prevented by the message containers not being able to connect.
2. After the application starts, start the message listeners.
3. If the connection to one or any of the message listeners goes down, it should attempt to automatically reconnect.
4. On application shutdown (such as the Tomcat being shutdown), the application should stop the message listeners and the cron job that processes the saved messages.
5. Make all of this testable (as in, be able to write integration tests for this setup).

Current Setup :

1. Spring Boot 1.5.6
2. Apache ZooKeeper 3.4.6
3. Apache ActiveMQ 5.7
4. Wicket 7.7.0

Work done so far :

1. Define a class that implements ApplicationListener<ApplicationReadyEvent> .
2. Setting the autoStart property of the DefaultMessageListenerContainer to false and start each container in the onApplicationEvent in a separate thread.

Questions :

1. Is it necessary to start each message container in its own thread? This seems to be overkill, but the way the "start" process works is that the DefaultMessageListenerContainer is built for that listener and then it is started. There is a UI component that a user can use to start/stop the message listeners if need be, and if these are started sequentially in one thread, then the latter three message containers could be null if the first one has yet to connect on startup.
2. How do I accomplish goals 4 and 5?

Of course, any commments on whether I am on the right track would be helpful.

Answer 1

If you do not start them in a custom thread then the whole application cannot be fully started. It is not just Wicket, but the Servlet container won't change the application state from STARTING to STARTED due to the blocking request to ZooKeeper.

Another option is to use a non-blocking request to ZooKeeper but this is done by the JMS client (ActiveMQ), so you need to check whether this is supported in their docs (both ActiveMQ and ZooKeeper). I haven't used those in several years, so I cannot help you more.