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package java.lang.reflect;
import java.lang.annotation.Annotation;
import java.lang.annotation.AnnotationFormatError;
import java.lang.annotation.Repeatable;
import java.util.Arrays;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.Objects;
import java.util.function.Function;
import java.util.stream.Collectors;
import sun.reflect.annotation.AnnotationSupport;
import sun.reflect.annotation.AnnotationType;
/**
* Represents an annotated construct of the program currently running
* in this VM.
*
* A construct is either an element or a type. Annotations on an
* element are on a declaration, whereas annotations on a
* type are on a specific use of a type name.
*
* As defined by The Java Language Specification
* section {@jls 9.7.4}, an annotation on an element is a
* declaration annotation and an annotation on a type is a
* type annotation.
*
* Note that any annotations returned by methods on the {@link
* AnnotatedType AnnotatedType} interface and its subinterfaces are
* type annotations as the entity being potentially annotated is a
* type. Annotations returned by methods outside of the {@code
* AnnotatedType} hierarchy are declaration annotations.
*
* This interface allows annotations to be read reflectively. All
* annotations returned by methods in this interface are immutable and
* serializable. The arrays returned by methods of this interface may
* be modified by callers without affecting the arrays returned to
* other callers.
*
*
The {@link #getAnnotationsByType(Class)} and {@link
* #getDeclaredAnnotationsByType(Class)} methods support multiple
* annotations of the same type on an element. If the argument to
* either method is a repeatable annotation type (JLS {@jls 9.6}),
* then the method will "look through" a container annotation (JLS
* {@jls 9.7}), if present, and return any annotations inside the
* container. Container annotations may be generated at compile-time
* to wrap multiple annotations of the argument type.
*
*
The terms directly present, indirectly present,
* present, and associated are used throughout this
* interface to describe precisely which annotations are returned by
* methods:
*
*
*
* - An annotation A is directly present on an
* element E if E has a {@code
* RuntimeVisibleAnnotations} or {@code
* RuntimeVisibleParameterAnnotations} or {@code
* RuntimeVisibleTypeAnnotations} attribute, and the attribute
* contains A.
*
*
- An annotation A is indirectly present on an
* element E if E has a {@code RuntimeVisibleAnnotations} or
* {@code RuntimeVisibleParameterAnnotations} or {@code RuntimeVisibleTypeAnnotations}
* attribute, and A 's type is repeatable, and the attribute contains
* exactly one annotation whose value element contains A and whose
* type is the containing annotation type of A 's type.
*
*
- An annotation A is present on an element E if either:
*
*
*
* - A is directly present on E; or
*
*
- No annotation of A 's type is directly present on
* E, and E is a class, and A 's type is
* inheritable, and A is present on the superclass of E.
*
*
*
* - An annotation A is associated with an element E
* if either:
*
*
*
* - A is directly or indirectly present on E; or
*
*
- No annotation of A 's type is directly or indirectly
* present on E, and E is a class, and A's type
* is inheritable, and A is associated with the superclass of
* E.
*
*
*
*
*
* The table below summarizes which kind of annotation presence
* different methods in this interface examine.
*
*
* Overview of kind of presence detected by different AnnotatedElement methods
*
* Method
* Kind of Presence
* Return Type
* Signature
* Directly Present
* Indirectly Present
* Present
* Associated
* {@code T}
* {@link #getAnnotation(Class) getAnnotation(Class<T>)}
* X {@code Annotation[]}
* {@link #getAnnotations getAnnotations()}
* X {@code T[]}
* {@link #getAnnotationsByType(Class) getAnnotationsByType(Class<T>)}
* X
* {@code T}
* {@link #getDeclaredAnnotation(Class) getDeclaredAnnotation(Class<T>)}
* X {@code Annotation[]}
* {@link #getDeclaredAnnotations getDeclaredAnnotations()}
* X {@code T[]}
* {@link #getDeclaredAnnotationsByType(Class) getDeclaredAnnotationsByType(Class<T>)}
* X X
*
* For an invocation of {@code get[Declared]AnnotationsByType(Class )},
* the order of annotations which are directly or indirectly
* present on an element E is computed as if indirectly present
* annotations on E are directly present on E in place
* of their container annotation, in the order in which they appear in
* the value element of the container annotation.
*
* There are several compatibility concerns to keep in mind if an
* annotation type T is originally not repeatable and
* later modified to be repeatable.
*
* The containing annotation type for T is TC.
*
*
*
* - Modifying T to be repeatable is source and binary
* compatible with existing uses of T and with existing uses
* of TC.
*
* That is, for source compatibility, source code with annotations of
* type T or of type TC will still compile. For binary
* compatibility, class files with annotations of type T or of
* type TC (or with other kinds of uses of type T or of
* type TC) will link against the modified version of T
* if they linked against the earlier version.
*
* (An annotation type TC may informally serve as an acting
* containing annotation type before T is modified to be
* formally repeatable. Alternatively, when T is made
* repeatable, TC can be introduced as a new type.)
*
*
- If an annotation type TC is present on an element, and
* T is modified to be repeatable with TC as its
* containing annotation type then:
*
*
*
* - The change to T is behaviorally compatible with respect
* to the {@code get[Declared]Annotation(Class
)} (called with an
* argument of T or TC) and {@code
* get[Declared]Annotations()} methods because the results of the
* methods will not change due to TC becoming the containing
* annotation type for T.
*
* - The change to T changes the results of the {@code
* get[Declared]AnnotationsByType(Class
)} methods called with an
* argument of T, because those methods will now recognize an
* annotation of type TC as a container annotation for T
* and will "look through" it to expose annotations of type T.
*
*
*
* - If an annotation of type T is present on an
* element and T is made repeatable and more annotations of
* type T are added to the element:
*
*
*
* - The addition of the annotations of type T is both
* source compatible and binary compatible.
*
*
- The addition of the annotations of type T changes the results
* of the {@code get[Declared]Annotation(Class
)} methods and {@code
* get[Declared]Annotations()} methods, because those methods will now
* only see a container annotation on the element and not see an
* annotation of type T.
*
* - The addition of the annotations of type T changes the
* results of the {@code get[Declared]AnnotationsByType(Class
)}
* methods, because their results will expose the additional
* annotations of type T whereas previously they exposed only a
* single annotation of type T.
*
*
*
*
*
* If an annotation returned by a method in this interface contains
* (directly or indirectly) a {@link Class}-valued member referring to
* a class that is not accessible in this VM, attempting to read the class
* by calling the relevant Class-returning method on the returned annotation
* will result in a {@link TypeNotPresentException}.
*
*
Similarly, attempting to read an enum-valued member will result in
* a {@link EnumConstantNotPresentException} if the enum constant in the
* annotation is no longer present in the enum class.
*
*
If an annotation type T is (meta-)annotated with an
* {@code @Repeatable} annotation whose value element indicates a type
* TC, but TC does not declare a {@code value()} method
* with a return type of T{@code []}, then an exception of type
* {@link java.lang.annotation.AnnotationFormatError} is thrown.
*
*
Finally, attempting to read a member whose definition has evolved
* incompatibly will result in a {@link
* java.lang.annotation.AnnotationTypeMismatchException} or an
* {@link java.lang.annotation.IncompleteAnnotationException}.
*
* @see java.lang.EnumConstantNotPresentException
* @see java.lang.TypeNotPresentException
* @see AnnotationFormatError
* @see java.lang.annotation.AnnotationTypeMismatchException
* @see java.lang.annotation.IncompleteAnnotationException
* @since 1.5
* @author Josh Bloch
*/
public interface AnnotatedElement {
/**
* Returns true if an annotation for the specified type
* is present on this element, else false. This method
* is designed primarily for convenient access to marker annotations.
*
*
The truth value returned by this method is equivalent to:
* {@code getAnnotation(annotationClass) != null}
*
* @implSpec The default implementation returns {@code
* getAnnotation(annotationClass) != null}.
*
* @param annotationClass the Class object corresponding to the
* annotation type
* @return true if an annotation for the specified annotation
* type is present on this element, else false
* @throws NullPointerException if the given annotation class is null
* @since 1.5
*/
default boolean isAnnotationPresent(Class annotationClass) {
return getAnnotation(annotationClass) != null;
}
/**
* Returns this element's annotation for the specified type if
* such an annotation is present, else null.
*
* @param the type of the annotation to query for and return if present
* @param annotationClass the Class object corresponding to the
* annotation type
* @return this element's annotation for the specified annotation type if
* present on this element, else null
* @throws NullPointerException if the given annotation class is null
* @since 1.5
*/
T getAnnotation(Class annotationClass);
/**
* Returns annotations that are present on this element.
*
* If there are no annotations present on this element, the return
* value is an array of length 0.
*
* The caller of this method is free to modify the returned array; it will
* have no effect on the arrays returned to other callers.
*
* @return annotations present on this element
* @since 1.5
*/
Annotation[] getAnnotations();
/**
* Returns annotations that are associated with this element.
*
* If there are no annotations associated with this element, the return
* value is an array of length 0.
*
* The difference between this method and {@link #getAnnotation(Class)}
* is that this method detects if its argument is a repeatable
* annotation type (JLS {@jls 9.6}), and if so, attempts to find one or
* more annotations of that type by "looking through" a container
* annotation.
*
* The caller of this method is free to modify the returned array; it will
* have no effect on the arrays returned to other callers.
*
* @implSpec The default implementation first calls {@link
* #getDeclaredAnnotationsByType(Class)} passing {@code
* annotationClass} as the argument. If the returned array has
* length greater than zero, the array is returned. If the returned
* array is zero-length and this {@code AnnotatedElement} is a
* class and the argument type is an inheritable annotation type,
* and the superclass of this {@code AnnotatedElement} is non-null,
* then the returned result is the result of calling {@link
* #getAnnotationsByType(Class)} on the superclass with {@code
* annotationClass} as the argument. Otherwise, a zero-length
* array is returned.
*
* @param the type of the annotation to query for and return if present
* @param annotationClass the Class object corresponding to the
* annotation type
* @return all this element's annotations for the specified annotation type if
* associated with this element, else an array of length zero
* @throws NullPointerException if the given annotation class is null
* @since 1.8
*/
default T[] getAnnotationsByType(Class annotationClass) {
/*
* Definition of associated: directly or indirectly present OR
* neither directly nor indirectly present AND the element is
* a Class, the annotation type is inheritable, and the
* annotation type is associated with the superclass of the
* element.
*/
T[] result = getDeclaredAnnotationsByType(annotationClass);
if (result.length == 0 && // Neither directly nor indirectly present
this instanceof Class && // the element is a class
AnnotationType.getInstance(annotationClass).isInherited()) { // Inheritable
Class superClass = ((Class) this).getSuperclass();
if (superClass != null) {
// Determine if the annotation is associated with the
// superclass
result = superClass.getAnnotationsByType(annotationClass);
}
}
return result;
}
/**
* Returns this element's annotation for the specified type if
* such an annotation is directly present, else null.
*
* This method ignores inherited annotations. (Returns null if no
* annotations are directly present on this element.)
*
* @implSpec The default implementation first performs a null check
* and then loops over the results of {@link
* #getDeclaredAnnotations} returning the first annotation whose
* annotation type matches the argument type.
*
* @param the type of the annotation to query for and return if directly present
* @param annotationClass the Class object corresponding to the
* annotation type
* @return this element's annotation for the specified annotation type if
* directly present on this element, else null
* @throws NullPointerException if the given annotation class is null
* @since 1.8
*/
default T getDeclaredAnnotation(Class annotationClass) {
Objects.requireNonNull(annotationClass);
// Loop over all directly-present annotations looking for a matching one
for (Annotation annotation : getDeclaredAnnotations()) {
if (annotationClass.equals(annotation.annotationType())) {
// More robust to do a dynamic cast at runtime instead
// of compile-time only.
return annotationClass.cast(annotation);
}
}
return null;
}
/**
* Returns this element's annotation(s) for the specified type if
* such annotations are either directly present or
* indirectly present. This method ignores inherited
* annotations.
*
* If there are no specified annotations directly or indirectly
* present on this element, the return value is an array of length
* 0.
*
* The difference between this method and {@link
* #getDeclaredAnnotation(Class)} is that this method detects if its
* argument is a repeatable annotation type (JLS {@jls 9.6}), and if so,
* attempts to find one or more annotations of that type by "looking
* through" a container annotation if one is present.
*
* The caller of this method is free to modify the returned array; it will
* have no effect on the arrays returned to other callers.
*
* @implSpec The default implementation may call {@link
* #getDeclaredAnnotation(Class)} one or more times to find a
* directly present annotation and, if the annotation type is
* repeatable, to find a container annotation. If annotations of
* the annotation type {@code annotationClass} are found to be both
* directly and indirectly present, then {@link
* #getDeclaredAnnotations()} will get called to determine the
* order of the elements in the returned array.
*
* Alternatively, the default implementation may call {@link
* #getDeclaredAnnotations()} a single time and the returned array
* examined for both directly and indirectly present
* annotations. The results of calling {@link
* #getDeclaredAnnotations()} are assumed to be consistent with the
* results of calling {@link #getDeclaredAnnotation(Class)}.
*
* @param the type of the annotation to query for and return
* if directly or indirectly present
* @param annotationClass the Class object corresponding to the
* annotation type
* @return all this element's annotations for the specified annotation type if
* directly or indirectly present on this element, else an array of length zero
* @throws NullPointerException if the given annotation class is null
* @since 1.8
*/
default T[] getDeclaredAnnotationsByType(Class annotationClass) {
Objects.requireNonNull(annotationClass);
return AnnotationSupport.
getDirectlyAndIndirectlyPresent(Arrays.stream(getDeclaredAnnotations()).
collect(Collectors.toMap(Annotation::annotationType,
Function.identity(),
((first,second) -> first),
LinkedHashMap::new)),
annotationClass);
}
/**
* Returns annotations that are directly present on this element.
* This method ignores inherited annotations.
*
* If there are no annotations directly present on this element,
* the return value is an array of length 0.
*
* The caller of this method is free to modify the returned array; it will
* have no effect on the arrays returned to other callers.
*
* @return annotations directly present on this element
* @since 1.5
*/
Annotation[] getDeclaredAnnotations();
}