Re: JDK 8 (initial) RFR for JDK-8005294 : Consider default methods for additions to AnnotatedElement

[Joe Darcy]

Hi Peter,

The concerns you raise below are some of the trade-offs I was thinking 
of as I was working on the current implementation :-)

From a specification perspective, I'd like the @implSpec for this 
method to allow different combinations of calling 
getDeclaredAnnotation(Class) and getDeclaredAnnotations.

There are several concerns which influence the performance of different 
implementation options for getDeclaredAnnotationsByType:

* How often (and by how much) is getDeclaredAnnotation(Class) faster 
than iterating over getDeclaredAnnotations?
* Related question: how many annotations does getDeclaredAnnotations return?
* How often is an annotation both directly present and indirectly 
present on the same element?

Depending on the assumptions one makes, an implementation that is 
primarily based on getDeclaredAnnotation(Class) (one to two calls with 
getDeclaredAnnotations as a backstop) can have better expected 
performance than a method that always does a single call to 
getDeclaredAnnotations. On the other hand, the 
getDeclaredAnnotations-based approach will have a better worst-case 
behavior (one call to another AnnotedElement method vs three calls).

I don't think the performance of this default method should be that 
important since in my estimation most AnnotatedElement implementations 
are in JDK and will have more optimized implementations based on 
lower-level data structures. We often try to improve the expected case 
performance vs the worst case so I would lean toward a 
getDeclaredAnnotation(Class)-based implementation rather than a soley 
getDeclaredAnnotations-based one.

Thanks for the comments,

-Joe

On 10/25/2013 08:56 AM, Peter Levart wrote:
Hi Joe,

The code below is more optimal only in AnnotatedElement 
implementations that don't override getDeclaredAnnotation(Class) with 
more optimal implementation based on a HashMap lookup. Your 
implementation avoids calling getDeclaredAnnotations() in common cases 
(where only directly present or only in-directly present annotations 
exist), but as this is a default method, it must be assumed that it 
will be invoked on AnnotatedElement implementations that don't 
override it and those presumably also don't override  default 
getDeclaredAnnotation(Class) which is based on 
getDeclaredAnnotations() and interation over returned elements. In 
this situation, your code does 2 (or in uncommon case 3) calls to 
getDeclaredAnnotations() with iteration over elements, while the below 
code only does 1...

On 10/25/2013 05:03 PM, Peter Levart wrote:
Hi Joe,

I propose some "premature" optimization for 
AnnotatedElement.getDeclaredAnnotationsByType(). This implementation 
calls either getDeclaredAnnotatios() once or 
getDeclaredAnnotation(Class) once, depending on whether the 
annotation type is repeatable or not respectively (this check also 
requires a getDeclaredAnnotation() call, but I propose to extend 
AnnotationType in the future to provide with cached containerClass 
directly). Also, it is about 7x faster to use 
annotationClass.isInstance(ann) to check for the type of annotation 
instead of ann.annotationType() == annotationClass which goes through 
annotation Proxy, etc...

Here it is:

    default <T extends Annotation> T[] 
getDeclaredAnnotationsByType(Class<T> annotationClass) {
        Objects.requireNonNull(annotationClass);
        Repeatable repeatable = 
annotationClass.getDeclaredAnnotation(Repeatable.class);

        // non-repeatable: just delegate to getDeclaredAnnotation and 
return wrapped result
        if (repeatable == null) {
            T ann = getDeclaredAnnotation(annotationClass);
            @SuppressWarnings("unchecked")
            T[] result = (T[]) Array.newInstance(annotationClass, ann 
== null ? 0 : 1);
            if (ann != null) result[0] = ann;
            return result;
        }

        // repeatable: iterate all declared annotations, find 
directly and indirectly present
        // and also determine the order (directlyPresentFirst)...
        Class<? extends Annotation> containerClass = repeatable.value();
        T directlyPresent = null;
        T[] indirectlyPresent = null;
        boolean directlyPresentFirst = false;
        for (Annotation ann : getDeclaredAnnotations()) {
            if (directlyPresent == null && 
annotationClass.isInstance(ann)) {
                directlyPresent = annotationClass.cast(ann);
                if (indirectlyPresent != null) {
                    break;
                }
            } else if (indirectlyPresent == null && 
containerClass.isInstance(ann)) {
                indirectlyPresent = AnnotationSupport.getValueArray(ann);
                if (directlyPresent != null) {
                    directlyPresentFirst = true;
                    break;
                }
            }
        }

        // concatenate directlyPresent and indirectlyPresent annotations
        @SuppressWarnings("unchecked")
        T[] result = (directlyPresent == null && indirectlyPresent != 
null)
                     ? indirectlyPresent
                     : (T[]) Array.newInstance(annotationClass,
                         (directlyPresent == null ? 0 : 1) +
                         (indirectlyPresent == null ? 0 : 
indirectlyPresent.length));

        if (directlyPresent != null) {
            if (indirectlyPresent == null || indirectlyPresent.length 
== 0) {
                result[0] = directlyPresent;
            } else {
                result[directlyPresentFirst ? 0 : 
indirectlyPresent.length] = directlyPresent;
                System.arraycopy(indirectlyPresent, 0, result,
                    directlyPresentFirst ? 1 : 0, 
indirectlyPresent.length);
            }
        }

        return result;
    }



Regards, Peter

On 10/25/2013 10:40 AM, Joe Darcy wrote:
Hi Joel and Peter,

On 10/24/2013 07:10 AM, Peter Levart wrote:
Hi Joe,

I see two problems with the implementation in 
*AnnotatedElementSupport*. The first is the treatment of 
declared-only annotations where the code returns either directly 
present or in-directly present repeatable annotations, but not 
both. So in the following example:

@Ann(1)
@AnnCont({@Ann(2), @Ann(3)})

it will only return [@Ann(1)], but I think it should return all of 
them [@Ann(1), @Ann(2), @Ann(3)] - does the spec. define that?


[snip]

From your feedback (and a closer reading of the specifciation), I've 
reworked the specifications and implemenations of the default 
methods for get[Declared]AnnotationsByType:

http://cr.openjdk.java.net/~darcy/8005294.2/

Tests still need to be written, but this implementation should be 
much closed to what is needed.

Thanks,

-Joe