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25  
26  package java.lang.reflect;
27  
28  import java.lang.annotation.Annotation;
29  import java.lang.annotation.AnnotationFormatError;
30  import java.lang.annotation.Repeatable;
31  import java.util.Arrays;
32  import java.util.LinkedHashMap;
33  import java.util.Map;
34  import java.util.Objects;
35  import java.util.function.Function;
36  import java.util.stream.Collectors;
37  import sun.reflect.annotation.AnnotationSupport;
38  import sun.reflect.annotation.AnnotationType;
39  
40  /**
41   * Represents an annotated element of the program currently running in this
42   * VM.  This interface allows annotations to be read reflectively.  All
43   * annotations returned by methods in this interface are immutable and
44   * serializable. The arrays returned by methods of this interface may be modified
45   * by callers without affecting the arrays returned to other callers.
46   *
47   * <p>The {@link #getAnnotationsByType(Class)} and {@link
48   * #getDeclaredAnnotationsByType(Class)} methods support multiple
49   * annotations of the same type on an element. If the argument to
50   * either method is a repeatable annotation type (JLS 9.6), then the
51   * method will "look through" a container annotation (JLS 9.7), if
52   * present, and return any annotations inside the container. Container
53   * annotations may be generated at compile-time to wrap multiple
54   * annotations of the argument type.
55   *
56   * <p>The terms <em>directly present</em>, <em>indirectly present</em>,
57   * <em>present</em>, and <em>associated</em> are used throughout this
58   * interface to describe precisely which annotations are returned by
59   * methods:
60   *
61   * <ul>
62   *
63   * <li> An annotation <i>A</i> is <em>directly present</em> on an
64   * element <i>E</i> if <i>E</i> has a {@code
65   * RuntimeVisibleAnnotations} or {@code
66   * RuntimeVisibleParameterAnnotations} or {@code
67   * RuntimeVisibleTypeAnnotations} attribute, and the attribute
68   * contains <i>A</i>.
69   *
70   * <li>An annotation <i>A</i> is <em>indirectly present</em> on an
71   * element <i>E</i> if <i>E</i> has a {@code RuntimeVisibleAnnotations} or
72   * {@code RuntimeVisibleParameterAnnotations} or {@code RuntimeVisibleTypeAnnotations}
73   * attribute, and <i>A</i> 's type is repeatable, and the attribute contains
74   * exactly one annotation whose value element contains <i>A</i> and whose
75   * type is the containing annotation type of <i>A</i> 's type.
76   *
77   * <li>An annotation <i>A</i> is present on an element <i>E</i> if either:
78   *
79   * <ul>
80   *
81   * <li><i>A</i> is directly present on <i>E</i>; or
82   *
83   * <li>No annotation of <i>A</i> 's type is directly present on
84   * <i>E</i>, and <i>E</i> is a class, and <i>A</i> 's type is
85   * inheritable, and <i>A</i> is present on the superclass of <i>E</i>.
86   *
87   * </ul>
88   *
89   * <li>An annotation <i>A</i> is <em>associated</em> with an element <i>E</i>
90   * if either:
91   *
92   * <ul>
93   *
94   * <li><i>A</i> is directly or indirectly present on <i>E</i>; or
95   *
96   * <li>No annotation of <i>A</i> 's type is directly or indirectly
97   * present on <i>E</i>, and <i>E</i> is a class, and <i>A</i>'s type
98   * is inheritable, and <i>A</i> is associated with the superclass of
99   * <i>E</i>.
100  *
101  * </ul>
102  *
103  * </ul>
104  *
105  * <p>The table below summarizes which kind of annotation presence
106  * different methods in this interface examine.
107  *
108  * <table border>
109  * <caption>Overview of kind of presence detected by different AnnotatedElement methods</caption>
110  * <tr><th colspan=2></th><th colspan=4>Kind of Presence</th>
111  * <tr><th colspan=2>Method</th><th>Directly Present</th><th>Indirectly Present</th><th>Present</th><th>Associated</th>
112  * <tr><td align=right>{@code T}</td><td>{@link #getAnnotation(Class) getAnnotation(Class&lt;T&gt;)}
113  * <td></td><td></td><td>X</td><td></td>
114  * </tr>
115  * <tr><td align=right>{@code Annotation[]}</td><td>{@link #getAnnotations getAnnotations()}
116  * <td></td><td></td><td>X</td><td></td>
117  * </tr>
118  * <tr><td align=right>{@code T[]}</td><td>{@link #getAnnotationsByType(Class) getAnnotationsByType(Class&lt;T&gt;)}
119  * <td></td><td></td><td></td><td>X</td>
120  * </tr>
121  * <tr><td align=right>{@code T}</td><td>{@link #getDeclaredAnnotation(Class) getDeclaredAnnotation(Class&lt;T&gt;)}
122  * <td>X</td><td></td><td></td><td></td>
123  * </tr>
124  * <tr><td align=right>{@code Annotation[]}</td><td>{@link #getDeclaredAnnotations getDeclaredAnnotations()}
125  * <td>X</td><td></td><td></td><td></td>
126  * </tr>
127  * <tr><td align=right>{@code T[]}</td><td>{@link #getDeclaredAnnotationsByType(Class) getDeclaredAnnotationsByType(Class&lt;T&gt;)}
128  * <td>X</td><td>X</td><td></td><td></td>
129  * </tr>
130  * </table>
131  *
132  * <p>For an invocation of {@code get[Declared]AnnotationsByType( Class <
133  * T >)}, the order of annotations which are directly or indirectly
134  * present on an element <i>E</i> is computed as if indirectly present
135  * annotations on <i>E</i> are directly present on <i>E</i> in place
136  * of their container annotation, in the order in which they appear in
137  * the value element of the container annotation.
138  *
139  * <p>There are several compatibility concerns to keep in mind if an
140  * annotation type <i>T</i> is originally <em>not</em> repeatable and
141  * later modified to be repeatable.
142  *
143  * The containing annotation type for <i>T</i> is <i>TC</i>.
144  *
145  * <ul>
146  *
147  * <li>Modifying <i>T</i> to be repeatable is source and binary
148  * compatible with existing uses of <i>T</i> and with existing uses
149  * of <i>TC</i>.
150  *
151  * That is, for source compatibility, source code with annotations of
152  * type <i>T</i> or of type <i>TC</i> will still compile. For binary
153  * compatibility, class files with annotations of type <i>T</i> or of
154  * type <i>TC</i> (or with other kinds of uses of type <i>T</i> or of
155  * type <i>TC</i>) will link against the modified version of <i>T</i>
156  * if they linked against the earlier version.
157  *
158  * (An annotation type <i>TC</i> may informally serve as an acting
159  * containing annotation type before <i>T</i> is modified to be
160  * formally repeatable. Alternatively, when <i>T</i> is made
161  * repeatable, <i>TC</i> can be introduced as a new type.)
162  *
163  * <li>If an annotation type <i>TC</i> is present on an element, and
164  * <i>T</i> is modified to be repeatable with <i>TC</i> as its
165  * containing annotation type then:
166  *
167  * <ul>
168  *
169  * <li>The change to <i>T</i> is behaviorally compatible with respect
170  * to the {@code get[Declared]Annotation(Class<T>)} (called with an
171  * argument of <i>T</i> or <i>TC</i>) and {@code
172  * get[Declared]Annotations()} methods because the results of the
173  * methods will not change due to <i>TC</i> becoming the containing
174  * annotation type for <i>T</i>.
175  *
176  * <li>The change to <i>T</i> changes the results of the {@code
177  * get[Declared]AnnotationsByType(Class<T>)} methods called with an
178  * argument of <i>T</i>, because those methods will now recognize an
179  * annotation of type <i>TC</i> as a container annotation for <i>T</i>
180  * and will "look through" it to expose annotations of type <i>T</i>.
181  *
182  * </ul>
183  *
184  * <li>If an annotation of type <i>T</i> is present on an
185  * element and <i>T</i> is made repeatable and more annotations of
186  * type <i>T</i> are added to the element:
187  *
188  * <ul>
189  *
190  * <li> The addition of the annotations of type <i>T</i> is both
191  * source compatible and binary compatible.
192  *
193  * <li>The addition of the annotations of type <i>T</i> changes the results
194  * of the {@code get[Declared]Annotation(Class<T>)} methods and {@code
195  * get[Declared]Annotations()} methods, because those methods will now
196  * only see a container annotation on the element and not see an
197  * annotation of type <i>T</i>.
198  *
199  * <li>The addition of the annotations of type <i>T</i> changes the
200  * results of the {@code get[Declared]AnnotationsByType(Class<T>)}
201  * methods, because their results will expose the additional
202  * annotations of type <i>T</i> whereas previously they exposed only a
203  * single annotation of type <i>T</i>.
204  *
205  * </ul>
206  *
207  * </ul>
208  *
209  * <p>If an annotation returned by a method in this interface contains
210  * (directly or indirectly) a {@link Class}-valued member referring to
211  * a class that is not accessible in this VM, attempting to read the class
212  * by calling the relevant Class-returning method on the returned annotation
213  * will result in a {@link TypeNotPresentException}.
214  *
215  * <p>Similarly, attempting to read an enum-valued member will result in
216  * a {@link EnumConstantNotPresentException} if the enum constant in the
217  * annotation is no longer present in the enum type.
218  *
219  * <p>If an annotation type <i>T</i> is (meta-)annotated with an
220  * {@code @Repeatable} annotation whose value element indicates a type
221  * <i>TC</i>, but <i>TC</i> does not declare a {@code value()} method
222  * with a return type of <i>T</i>{@code []}, then an exception of type
223  * {@link java.lang.annotation.AnnotationFormatError} is thrown.
224  *
225  * <p>Finally, attempting to read a member whose definition has evolved
226  * incompatibly will result in a {@link
227  * java.lang.annotation.AnnotationTypeMismatchException} or an
228  * {@link java.lang.annotation.IncompleteAnnotationException}.
229  *
230  * @see java.lang.EnumConstantNotPresentException
231  * @see java.lang.TypeNotPresentException
232  * @see AnnotationFormatError
233  * @see java.lang.annotation.AnnotationTypeMismatchException
234  * @see java.lang.annotation.IncompleteAnnotationException
235  * @since 1.5
236  * @author Josh Bloch
237  */
238 public interface AnnotatedElement {
239     /**
240      * Returns true if an annotation for the specified type
241      * is <em>present</em> on this element, else false.  This method
242      * is designed primarily for convenient access to marker annotations.
243      *
244      * <p>The truth value returned by this method is equivalent to:
245      * {@code getAnnotation(annotationClass) != null}
246      *
247      * <p>The body of the default method is specified to be the code
248      * above.
249      *
250      * @param annotationClass the Class object corresponding to the
251      *        annotation type
252      * @return true if an annotation for the specified annotation
253      *     type is present on this element, else false
254      * @throws NullPointerException if the given annotation class is null
255      * @since 1.5
256      */
257     default boolean isAnnotationPresent(Class<? extends Annotation> annotationClass) {
258         return getAnnotation(annotationClass) != null;
259     }
260 
261    /**
262      * Returns this element's annotation for the specified type if
263      * such an annotation is <em>present</em>, else null.
264      *
265      * @param <T> the type of the annotation to query for and return if present
266      * @param annotationClass the Class object corresponding to the
267      *        annotation type
268      * @return this element's annotation for the specified annotation type if
269      *     present on this element, else null
270      * @throws NullPointerException if the given annotation class is null
271      * @since 1.5
272      */
273     <T extends Annotation> T getAnnotation(Class<T> annotationClass);
274 
275     /**
276      * Returns annotations that are <em>present</em> on this element.
277      *
278      * If there are no annotations <em>present</em> on this element, the return
279      * value is an array of length 0.
280      *
281      * The caller of this method is free to modify the returned array; it will
282      * have no effect on the arrays returned to other callers.
283      *
284      * @return annotations present on this element
285      * @since 1.5
286      */
287     Annotation[] getAnnotations();
288 
289     /**
290      * Returns annotations that are <em>associated</em> with this element.
291      *
292      * If there are no annotations <em>associated</em> with this element, the return
293      * value is an array of length 0.
294      *
295      * The difference between this method and {@link #getAnnotation(Class)}
296      * is that this method detects if its argument is a <em>repeatable
297      * annotation type</em> (JLS 9.6), and if so, attempts to find one or
298      * more annotations of that type by "looking through" a container
299      * annotation.
300      *
301      * The caller of this method is free to modify the returned array; it will
302      * have no effect on the arrays returned to other callers.
303      *
304      * @implSpec The default implementation first calls {@link
305      * #getDeclaredAnnotationsByType(Class)} passing {@code
306      * annotationClass} as the argument. If the returned array has
307      * length greater than zero, the array is returned. If the returned
308      * array is zero-length and this {@code AnnotatedElement} is a
309      * class and the argument type is an inheritable annotation type,
310      * and the superclass of this {@code AnnotatedElement} is non-null,
311      * then the returned result is the result of calling {@link
312      * #getAnnotationsByType(Class)} on the superclass with {@code
313      * annotationClass} as the argument. Otherwise, a zero-length
314      * array is returned.
315      *
316      * @param <T> the type of the annotation to query for and return if present
317      * @param annotationClass the Class object corresponding to the
318      *        annotation type
319      * @return all this element's annotations for the specified annotation type if
320      *     associated with this element, else an array of length zero
321      * @throws NullPointerException if the given annotation class is null
322      * @since 1.8
323      */
324     default <T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass) {
325          /*
326           * Definition of associated: directly or indirectly present OR
327           * neither directly nor indirectly present AND the element is
328           * a Class, the annotation type is inheritable, and the
329           * annotation type is associated with the superclass of the
330           * element.
331           */
332          T[] result = getDeclaredAnnotationsByType(annotationClass);
333 
334          if (result.length == 0 && // Neither directly nor indirectly present
335              this instanceof Class && // the element is a class
336              AnnotationType.getInstance(annotationClass).isInherited()) { // Inheritable
337              Class<?> superClass = ((Class<?>) this).getSuperclass();
338              if (superClass != null) {
339                  // Determine if the annotation is associated with the
340                  // superclass
341                  result = superClass.getAnnotationsByType(annotationClass);
342              }
343          }
344 
345          return result;
346      }
347 
348     /**
349      * Returns this element's annotation for the specified type if
350      * such an annotation is <em>directly present</em>, else null.
351      *
352      * This method ignores inherited annotations. (Returns null if no
353      * annotations are directly present on this element.)
354      *
355      * @implSpec The default implementation first performs a null check
356      * and then loops over the results of {@link
357      * #getDeclaredAnnotations} returning the first annotation whose
358      * annotation type matches the argument type.
359      *
360      * @param <T> the type of the annotation to query for and return if directly present
361      * @param annotationClass the Class object corresponding to the
362      *        annotation type
363      * @return this element's annotation for the specified annotation type if
364      *     directly present on this element, else null
365      * @throws NullPointerException if the given annotation class is null
366      * @since 1.8
367      */
368     default <T extends Annotation> T getDeclaredAnnotation(Class<T> annotationClass) {
369          Objects.requireNonNull(annotationClass);
370          // Loop over all directly-present annotations looking for a matching one
371          for (Annotation annotation : getDeclaredAnnotations()) {
372              if (annotationClass.equals(annotation.annotationType())) {
373                  // More robust to do a dynamic cast at runtime instead
374                  // of compile-time only.
375                  return annotationClass.cast(annotation);
376              }
377          }
378          return null;
379      }
380 
381     /**
382      * Returns this element's annotation(s) for the specified type if
383      * such annotations are either <em>directly present</em> or
384      * <em>indirectly present</em>. This method ignores inherited
385      * annotations.
386      *
387      * If there are no specified annotations directly or indirectly
388      * present on this element, the return value is an array of length
389      * 0.
390      *
391      * The difference between this method and {@link
392      * #getDeclaredAnnotation(Class)} is that this method detects if its
393      * argument is a <em>repeatable annotation type</em> (JLS 9.6), and if so,
394      * attempts to find one or more annotations of that type by "looking
395      * through" a container annotation if one is present.
396      *
397      * The caller of this method is free to modify the returned array; it will
398      * have no effect on the arrays returned to other callers.
399      *
400      * @implSpec The default implementation may call {@link
401      * #getDeclaredAnnotation(Class)} one or more times to find a
402      * directly present annotation and, if the annotation type is
403      * repeatable, to find a container annotation. If annotations of
404      * the annotation type {@code annotationClass} are found to be both
405      * directly and indirectly present, then {@link
406      * #getDeclaredAnnotations()} will get called to determine the
407      * order of the elements in the returned array.
408      *
409      * <p>Alternatively, the default implementation may call {@link
410      * #getDeclaredAnnotations()} a single time and the returned array
411      * examined for both directly and indirectly present
412      * annotations. The results of calling {@link
413      * #getDeclaredAnnotations()} are assumed to be consistent with the
414      * results of calling {@link #getDeclaredAnnotation(Class)}.
415      *
416      * @param <T> the type of the annotation to query for and return
417      * if directly or indirectly present
418      * @param annotationClass the Class object corresponding to the
419      *        annotation type
420      * @return all this element's annotations for the specified annotation type if
421      *     directly or indirectly present on this element, else an array of length zero
422      * @throws NullPointerException if the given annotation class is null
423      * @since 1.8
424      */
425     default <T extends Annotation> T[] getDeclaredAnnotationsByType(Class<T> annotationClass) {
426         Objects.requireNonNull(annotationClass);
427         return AnnotationSupport.
428             getDirectlyAndIndirectlyPresent(Arrays.stream(getDeclaredAnnotations()).
429                                             collect(Collectors.toMap(Annotation::annotationType,
430                                                                      Function.identity(),
431                                                                      ((first,second) -> first),
432                                                                      LinkedHashMap::new)),
433                                             annotationClass);
434     }
435 
436     /**
437      * Returns annotations that are <em>directly present</em> on this element.
438      * This method ignores inherited annotations.
439      *
440      * If there are no annotations <em>directly present</em> on this element,
441      * the return value is an array of length 0.
442      *
443      * The caller of this method is free to modify the returned array; it will
444      * have no effect on the arrays returned to other callers.
445      *
446      * @return annotations directly present on this element
447      * @since 1.5
448      */
449     Annotation[] getDeclaredAnnotations();
450 }