Question

I have a bunch of projects which declare some spring bean files. I would like to write a “library” which supplies a utility which takes some bean names and adds some behaviour “around” the objects (example: Call Counting, Monitoring, Logging etc)

One obvious way for doing this would be to add some AspectJ annotations in the spring xml files in the projects but I would like the “utility” to search for some beans and add behaviour to them (This way the projects themselves are not aware of the utility).

The utility will be declared in the spring xml file somewhere so it has access to the ApplicationContext as it could implement ApplicationContextAware interface however I am keen on exploring how one would go about modifying behaviour of another bean in the app context programmatically. ex, something like find a bean of id “OrderService”, create an aspected bean with some monitoring/call counting etc around all methods and replace that bean in the application context for “OrderService”

I know there are disadvantages with this approach but what I am after is “IS it possible to do this? And if yes how?”

Answer 1

If you don’t want to use AOP, you can achieve this using a BeanPostProcessor. The Spring documentation states:

The BeanPostProcessor interface defines callback methods that you can
implement to provide your own (or override the container’s default)
instantiation logic, dependency-resolution logic, and so forth. If you
want to implement some custom logic after the Spring container
finishes instantiating, configuring, and otherwise initializing a
bean, you can plug in one or more BeanPostProcessor implementations.

So you may create and register a BeanPostProcessor and implement the postProcessAfterInitialization(Object bean, String beanName) method to modify the methods you want to customize. Here is an example.

(But I would still recommend that you do this with AOP as this is the classical use case for it and it’s much easier and more declarative. With the bean() pointcut, you can even advise beans with names matching a certain pattern.)