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annotations not following inheritance

Pat Farrell
Rancher

Joined: Aug 11, 2007
Posts: 4646
    
    5

I'm using Bear's frontman, and have to classes, the top explicitly says "implements Command" and the subclass has the annotation.

public abstract class CommandBase implements Command {


@FrontmanCommand("confirm")
public class ConfirmEmail extends CommandBase{


This fails at runtime, as FrontMan can't find a class that has the annotation and does the implementation.

To my eyes, this version is exactly the same, expect it explicitly includes the "implements Command" rather than just inheriting
that it does the "implements Command"

@FrontmanCommand("confirm")
public class ConfirmEmail extends CommandBase implements Command {


Is this a bug in FrontMan? or my thinking? or something else?
thanks
pat
Bear Bibeault
Author and ninkuma
Marshal

Joined: Jan 10, 2002
Posts: 61092
    
  66

It's a "pseudo bug".

Java has no way of asking "please find all the classes that are annotated with such-and-such an annotation", so everyone kind of rolls their own, and I've yet to find a bullet-proof implementation. Apparently, it's not an easy problem as evidenced by the sounds of crickets when I asked how Hibernate does it.

The algorithm that FrontMan is currently using requires that the implements Command be on the class that posesses the annotation. If it's an extending class (something I also frequently do), you just need to remember to repeat the implements on the extended class.

I still search for a better way.


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David Newton
Author
Rancher

Joined: Sep 29, 2008
Posts: 12617

There are some implementation in Struts 2's convention plugin if you're interested; haven't looked at them myself. I assume you've seen the Bill Burke project (http://bill.burkecentral.com/2008/01/14/scanning-java-annotations-at-runtime/ for some info).
 
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