[JSR308] Modifying the annotations in the source

Mahmood Ali mahmood at MIT.EDU
Thu Jan 22 20:52:07 EST 2009

Greetings Niko,

> Is it possible for a Checker to affect the annotations which will be
> written into the .class file?
The compiler public API only provides a read-only view of the trees  
and the java symbols.

It's possible to manipulate the compiler structures by casting them to  
the javac internal structure and manipulating the annotations fields  
(e.g. Tree to JCTree and Element to Symbol). The approach is a bit of  
gotcha points though:
1. A tree clean up routine is invoked after annotation processing  
phase.  As far as I can tell/remember it only removes the Symbol  
information from the tree, so it would be recalculated later.  If you  
simply manipulate the Element information, those changes might be lost  
before reaching code generation stage.  Also, you would need to use  
the AnnotationMirror compiler implementation (Attribute.Compound)  
rather than you own.

2. You might be better off, manipulating the tree itself, by using  
TreeMaker.  This page (http://www.ahristov.com/tutorial/java-compiler/new-operator.html 
) explains some of the TreeMaker API points.  However, the code  
samples aren't applicable to your case directly.

3. The List structures in the compiler (to hold annotations of a  
symbol) is an immutable List.  .add() methods throw an Exception, so  
you should use append() which returns a new List.  Hence, the pattern  
in the compiler of:
     mods.annotations = mods.annotations.appendList(atype.annotations);

4. You should never reuse generated trees of annotation mirrors, i.e.  
create one Attribute.Compound and add to multiple methods.  You would  
need to create a new one for each use.

Another approach is to have the checker output an annotation file then  
have the insert-annotation utility tool (http://groups.csail.mit.edu/pag/jsr308/annotation-file-utilities/ 
) insert the annotations to the class files afterwards.

Hope this helps.


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