io.avaje.prism.package-info Maven / Gradle / Ivy
/*
Copyright (c) 2006,2007, Bruce Chapman
All rights reserved.
Redistribution and use in source and binary forms, with or without modification,
are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice,
this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation and/or
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* Neither the name of the Hickory project nor the names of its contributors
may be used to endorse or promote products derived from this software without
specific prior written permission.
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*/
/*
* package-info.java
*
* Created on 12 August 2006, 20:44
*
*/
/**
* Annotations and processors for creating Prisms which are partial reflections of known
* annotations.
*
* The problem: When writing annotation processors the two conventional mechanisms to access the
* annotations in the source code are both awkward. {@code Element.getAnnotation()} can throw
* Exceptions if the annotation being modelled is not semantically correct, and the member methods
* on the returned Annotation can also throw Exceptions if the annotation being modelled is not
* semantically correct. Moreover when calling a member with a {@code Class} return type, you need
* to catch an exception to extract the TypeMirror.
*
*
On the other hand, AnnotationMirror and AnnotationValue do a good job of modelling both
* correct and incorrect annotations, but provide no simple mechanism to determine whether it is
* correct or incorrect, and provide no convenient functionality to access the member values in a
* simple type specific way. While AnnotationMirror and AnnotationValue provide an ideal mechanism
* for dealing with unknown annotations, they are inconvenient for reading member values from known
* annotations.
*
*
A Prism provides a solution to this problem by combining the advantages of the pure reflective
* model of AnnotationMirror and the runtime (real) model provided by {@code
* Element.getAnnotation()}, hence the term Prism to capture this idea of partial reflection.
*
*
A Mirror is where you look for a reflection whereas a Prism is where you look for a partial
* reflection. A {@code Prism} provides a partially reflective and partially real view of an {@code
* Annotation}.
*
*
A Prism class is generated by using the {@code @GeneratePrism} annotation, or several can be
* grouped together using {@code @GeneratePrisms}. The generated prisms have a complete set of
* javadoc for reference.
*
*
An instance of a Prism is obtained by calling the generated prism's factory method {@code
* getInstance(AnnotationMirror)} to obtain a prism corresponding to an annotation mirror, or the
* factory method {@code getInstanceOn(Element)} to obtain an instance corresponding to an
* annotation on the specified Element.
*
*
A prism has the same member methods as the annotation except that the return types are
* translated from runtime types to compile time types as follows...
*
*
* - Primitive members return their equivalent wrapper class in the prism.
*
- Class members return a {@link javax.lang.model.type.TypeMirror TypeMirror} from the mirror
* API.
*
- Enum members return a String being the name of the enum constant (because the constant
* value in the mirror API might not match those available in the runtime it cannot
* consistently return the appropriate enum).
*
- String members return Strings.
*
- Annotation members return a Prism of the annotation. If a prism for that annotation is
* generated from the same @GeneratePrisms annotation as the prism that uses it, then an
* instance of that prism will be returned. Otherwise a Prism for that annotation is supplied
* as an inner class of the dependant Prism. the name of which is the simple name of the
* referenced annotation type.
*
- Array members return a {@code List
} where X is the appropriate prism mapping of the
* array component as above.
*
*
* If a prism instance represents a semantically incorrect annotation then its {@code isValid} field
* will be false, and the member(s) with the erroneous value will return null. If {@code isValid} is
* {@code true} then no members will return null. AnnotatonProcessors using a prism should ignore
* any prism instance that is invalid. It can be assumed that the processing tool itself will
* indicate an error to the user in this case.
*
* The {@code mirror} field provides access to the underlying AnnotationMirror to assist with
* using the Messager.
*
*
The {@code values} field contains an object whose methods have the same signature as the
* annotation's methods but return the corresponding AnnotationValue or null if that member of the
* Annotation does not have a value. This is provided for use when using Messager which can take an
* AnnotationValue as a hint as to the message's position in the source code.
*
*
To generate a prism of a known annotation to be used by an AnnotationProcessor, use the {@link
* io.avaje.prism.GeneratePrism @GeneratePrism} annotation on either the Processor itself, or the
* package, compile once and the prism should be generated. The Processor for {@code @GeneratePrism}
* will be discovered automatically using the {@link java.util.ServiceLoader} mechanism if the
* annotation processing tool supports that means of discovery process.
*
*
If the processor needs to access prisms for more than one annotation type, use {@link
* io.avaje.prism.GeneratePrisms @GeneratePrisms} to group together all the {@code @GeneratePrism}
* annotations needed.
*/
@GeneratePrism(GeneratePrisms.class)
package io.avaje.prism;