Java and @annotations

Question

There's something I'm not sure to understand when it comes to using Java annotations. Here is an example :

I create a @Log annotation and add some functionality with it (every method annotated with @Log runs some log before executing the method).

Now I'm creating a new @SuperLog annotation like this one :

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Log
public @interface SuperLog {
     ............
}

This @SuperLog must provide all the stuff @Log does, plus some extra stuff specific to @SuperLog.

Unfortunately when I'm executing some methods annotated with @SuperLog, the log specific to @Log doesn't execute.

I don't understand why : the fact @SuperLog is annotated with @Log doesn't mean it "inherits" properties from @Log ? Shouldn't @SuperLog do every thing @Log is supposed to do?

score 6 · Accepted Answer · answered May 25 '18 at 17:56

6

As this question outlines, there is no inheritance of annotations.

And beyond that: keep in mind that annotations (mainly) get meaning at runtime because some framework reacts to their presence.

In other words: you could create a framework that somehow supports annotations coming with an inheritance tree. But assuming you are working with some existing framework, you have to accept what this framework is doing.

answered May 25 '18 at 17:56

GhostCat

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Thanks but with SpringBootApplication annotation, I noticed it is annotated with ComponentScan, EnableAutoConfiguration etc.. And this SpringBootApplication annotation does provide all services provided by these other annotations. So it does look like there's some "inheritance" – AntonBoarf May 25 '18 at 18:03
1

@AntonBoarf As said, this depends on what exactly the framework is doing. In other words: when the framework does `instanceof` , then "inheritance" isn't supported. But when the framework "scans" each annotation, it can very well determine such inherited aspects. – GhostCat May 25 '18 at 18:05
1

So does that mean that when (taking my first example) I annotated my SuperLog annotation with Log annotation, by default it does nothing. I must be in charge of noticing that SuperLog is annotated with Log and implement myself the logic I want, correct ? – AntonBoarf May 25 '18 at 18:09
That is the conclusion I would make here, too. – GhostCat May 28 '18 at 19:54

score 1 · Answer 2 · answered May 28 '18 at 00:15

I guess you 'execute some methods annotated @SuperLog' means use 'Spring AOP'.

As GhostCat said, the inheritance is depends on framework's implementation. And unfortunately Spring AOP pointcut doesn't support meta-annotation yet.

You can follow this spring improvement.

Java and @annotations

2 Answers2