Say I have a class with a few fields all marked with a custom annotation. In my case it is @inject, because this is being used for dependency injection. How can I run a method in a separate class each time that annotation is used in my a class? In other words, each time a class is loaded the annotation runs a method that will collect the field data and in turn set the field.
I already have the entire system set up for collecting the resources, but I need some direction on how to actually run that code when the class with @inject annotation is loaded. Is this something that can be done by defining some sort of method in the annotation interface that performs the data collection?
My initial thought is to use a custom class loader, but I don’t want to have to set the class loader when I use this jar in other projects. Is there a way to set a custom class loader programmatically for specific classes at runtime? I’m already doing a lot of pre-runtime reflection stuff and i’ll already know which classes need to be loaded with a custom loader. Its just a matter of not knowing or if its even possible to set a custom loader on a class from within the code.
Can a classloader even be used to perform tasks such as pre-populating fields, or am I running off on a wrong tangent here? I just need a little direction on the most common way this type of thing is done (pre-populating class fields at runtime).
I was overthinking this problem. You cannot actually run code automatically prior to loading a class (unless its a servlet filter etc). In my situation the answer was to create an instance based on a specific class that already held the resource data I needed. Similar to how Google’s Guice does it.
See this question for more insight: How does Guice Populate Annotated Fields