Question

Is it possible to do something like the following:

public void doStuff(@RequirePrivilege("foo") User user) {
    // ...
}

and have it effectively run as if it were the following?

public void doStuff(User user) {
    if(!user.hasPrivilege("foo"))
        throw new UserHasInsufficientPrivileges(); // this is a RuntimeException
    // ...
}

I know that Spring has various sorts of AOP support, but the best I could find was AOP code which was annotated so that it would execute before or after a specific method. I want to do the inverse and annotate the code that should be changed.

Ultimately I could just do the above check inside the method, but the annotation way of doing things provides additional documentation which makes it obvious that the user requires a particular privilege without having to keep the documentation in sync with the code.

Answer 1

You can look at using AspectJ for doing this, as it will match on annotations. You can then use an around aspect to decide if the user meets the requirements to use this method.

Spring allows you to use AspectJ, and I would suggest that if possible you not do this at run-time, but at compile-time, as there is no reason to pay the price for using this aspect whenever you start the application. But, if you must do it at run-time then that is doable, to me I try to use compile-time as much as possible.

You may want to look at AspectJ In Action (http://www.manning.com/laddad2/) but here is an example from there:
Signature pattern:

* *(@RequestParam
(@Sensitive *))

Description

*Any method with one parameter marked with the @RequestParam annotations and the parameter’s type is marked with the @Sensitive annotation.*

Example

void create(@RequestParam
MedicalRecord mr), assuming
MedicalRecord carries the
@Sensitive annotation.