Can I replace a Spring bean definition at runtime?

Question

Consider the following scenario. I have a Spring application context with a bean whose properties should be configurable, think DataSource or MailSender

Answer 1

Option 1 :

1. Inject the configurable bean into the DataSource or MailSender. Always get the configurable values from the configuration bean from within these beans.
2. Inside the configurable bean run a thread to read the externally configurable properties (file etc..) periodically. This way the configurable bean will refresh itself after the admin had changed the properties and so the DataSource will get the updated values automatically.
   • You need not actually implement the "thread" - read : http://commons.apache.org/configuration/userguide/howto_filebased.html#Automatic_Reloading

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Option 2 (bad, i think, but maybe not - depends on use case) :

1. Always create new beans for beans of type DataSource / MailSender - using prototype scope. In the init of the bean, read the properties afresh.

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Option 3 : I think, @mR_fr0g suggestion on using JMX might not be a bad idea. What you could do is :

1. expose your configuration bean as a MBean (read http://static.springsource.org/spring/docs/2.5.x/reference/jmx.html)
2. Ask your admin to change the configuration properties on the MBean (or provide an interface in the bean to trigger property updates from their source)
3. This MBean (a new piece of java code that you will need to write), MUST keep references of Beans (the ones that you want to change / inject the changed properties into). This should be simple (via setter injection or runtime fetch of bean names / classes)
   1. When the property on the MBean is changed (or triggered), it must call the appropriate setters on the respective beans. That way, your legacy code does not change, you can still manage runtime property changes.

HTH!