Spring5源码解析-使用Spring AnnotationUtils处理注解
通过Java中的注解,程序员可以将配置文件中的一些配置通过使用Java类来实现。例如,在Spring中,通过@RequestMapping
注解,我们可以直接在controller
内配置URL映射
。一般来说,成功者的背后离不开一帮默默支持他的小伙伴,这里同样是,一旦离开其中一个,就甭指望实现所期望的功能,这里要说的一个就是AnnotationUtils
。
在本文中,我们将会看到AnnotationUtils类是如何给我们提供极大的便利的。首先,我们将关注下其所有可用的方法。进而,我们来看看这些方法用在了什么地方。最后,老规矩,Demo。
代码截的不少,主要还是为了在平时不一定有IDE环境下清楚的看清弄懂上下文的调用关系,也方面读者可以快速的找到相应的代码所在地。
另外,这一篇融合了前面很多篇的细节,有些不清晰明了的地方,请回头看前面的系列。
什么是Spring中的AnnotationUtils类?
AnnotationUtils
是一个专门用于处理复杂注解问题的类。其主要由公共和静态方法组成,它允许在类,方法或字段上检查注解。另外,AnnotationUtils
不仅仅来做简单的类分析。它也通过查找在超类和接口上的注解来做更多的事情。基于反射的API,AnnotationUtils
使用java.lang.reflect的 3个元素来处理注解:
- Annotation:表示注解。
- AnnotatedElement:表示被注解元素。
- Method:提供某些类或接口中的方法的信息。
现在,我们来看看AnnotationUtils
类中的最重要的几个public 方法:
- getAnnotation:有3个这样的名字的方法存在。 第一个接收参数
Annotation的对象实例
。第二个是AnnotatedElement
的实例。第三个getAnnotation
方法接收参数Method
对象。它们都从字段,类或方法得到并返回注解。
/**
* Get a single {@link Annotation} of {@code annotationType} from the supplied
* annotation: either the given annotation itself or a direct meta-annotation
* thereof.
* <p>Note that this method supports only a single level of meta-annotations.
* For support for arbitrary levels of meta-annotations, use one of the
* {@code find*()} methods instead.
* @param ann the Annotation to check
* @param annotationType the annotation type to look for, both locally and as a meta-annotation
* @return the first matching annotation, or {@code null} if not found
* @since 4.0
*/
@SuppressWarnings("unchecked")
@Nullable
public static <A extends Annotation> A getAnnotation(Annotation ann, Class<A> annotationType) {
if (annotationType.isInstance(ann)) {
return synthesizeAnnotation((A) ann);
}
Class<? extends Annotation> annotatedElement = ann.annotationType();
try {
return synthesizeAnnotation(annotatedElement.getAnnotation(annotationType), annotatedElement);
}
catch (Throwable ex) {
handleIntrospectionFailure(annotatedElement, ex);
return null;
}
}
/**
* Get a single {@link Annotation} of {@code annotationType} from the supplied
* {@link AnnotatedElement}, where the annotation is either <em>present</em> or
* <em>meta-present</em> on the {@code AnnotatedElement}.
* <p>Note that this method supports only a single level of meta-annotations.
* For support for arbitrary levels of meta-annotations, use
* {@link #findAnnotation(AnnotatedElement, Class)} instead.
* @param annotatedElement the {@code AnnotatedElement} from which to get the annotation
* @param annotationType the annotation type to look for, both locally and as a meta-annotation
* @return the first matching annotation, or {@code null} if not found
* @since 3.1
*/
@Nullable
public static <A extends Annotation> A getAnnotation(AnnotatedElement annotatedElement, Class<A> annotationType) {
try {
A annotation = annotatedElement.getAnnotation(annotationType);
if (annotation == null) {
for (Annotation metaAnn : annotatedElement.getAnnotations()) {
annotation = metaAnn.annotationType().getAnnotation(annotationType);
if (annotation != null) {
break;
}
}
}
return (annotation != null ? synthesizeAnnotation(annotation, annotatedElement) : null);
}
catch (Throwable ex) {
handleIntrospectionFailure(annotatedElement, ex);
return null;
}
}
/**
* Get a single {@link Annotation} of {@code annotationType} from the
* supplied {@link Method}, where the annotation is either <em>present</em>
* or <em>meta-present</em> on the method.
* <p>Correctly handles bridge {@link Method Methods} generated by the compiler.
* <p>Note that this method supports only a single level of meta-annotations.
* For support for arbitrary levels of meta-annotations, use
* {@link #findAnnotation(Method, Class)} instead.
* @param method the method to look for annotations on
* @param annotationType the annotation type to look for
* @return the first matching annotation, or {@code null} if not found
* @see org.springframework.core.BridgeMethodResolver#findBridgedMethod(Method)
* @see #getAnnotation(AnnotatedElement, Class)
*/
@Nullable
public static <A extends Annotation> A getAnnotation(Method method, Class<A> annotationType) {
Method resolvedMethod = BridgeMethodResolver.findBridgedMethod(method);
return getAnnotation((AnnotatedElement) resolvedMethod, annotationType);
}
- getRepeatableAnnotations:通过向参数中传递
AnnotatedElement
和所要查找的注解类型
来访问,有两个使用此名称的方法。 这两个方法从所提供的AnnotatedElement
上得到可重复的注解(即传入的annotationType
)对应的元素。例如,它可以返回使用@RequestMapping
注解所注解的方法(请看下面的源码)。
/**
* Get the <em>repeatable</em> {@linkplain Annotation annotations} of
* {@code annotationType} from the supplied {@link AnnotatedElement}, where
* such annotations are either <em>present</em>, <em>indirectly present</em>,
* or <em>meta-present</em> on the element.
* <p>This method mimics the functionality of Java 8's
* {@link java.lang.reflect.AnnotatedElement#getAnnotationsByType(Class)}
* with support for automatic detection of a <em>container annotation</em>
* declared via @{@link java.lang.annotation.Repeatable} (when running on
* Java 8 or higher) and with additional support for meta-annotations.
* <p>Handles both single annotations and annotations nested within a
* <em>container annotation</em>.
* <p>Correctly handles <em>bridge methods</em> generated by the
* compiler if the supplied element is a {@link Method}.
* <p>Meta-annotations will be searched if the annotation is not
* <em>present</em> on the supplied element.
* @param annotatedElement the element to look for annotations on
* @param annotationType the annotation type to look for
* @return the annotations found or an empty set (never {@code null})
* @since 4.2
* @see #getRepeatableAnnotations(AnnotatedElement, Class, Class)
* @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class, Class)
* @see AnnotatedElementUtils#getMergedRepeatableAnnotations(AnnotatedElement, Class)
* @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
* @see java.lang.annotation.Repeatable
* @see java.lang.reflect.AnnotatedElement#getAnnotationsByType
*/
@Nullable
public static <A extends Annotation> Set<A> getRepeatableAnnotations(AnnotatedElement annotatedElement,
Class<A> annotationType) {
return getRepeatableAnnotations(annotatedElement, annotationType, null);
}
/**
* Get the <em>repeatable</em> {@linkplain Annotation annotations} of
* {@code annotationType} from the supplied {@link AnnotatedElement}, where
* such annotations are either <em>present</em>, <em>indirectly present</em>,
* or <em>meta-present</em> on the element.
* <p>This method mimics the functionality of Java 8's
* {@link java.lang.reflect.AnnotatedElement#getAnnotationsByType(Class)}
* with additional support for meta-annotations.
* <p>Handles both single annotations and annotations nested within a
* <em>container annotation</em>.
* <p>Correctly handles <em>bridge methods</em> generated by the
* compiler if the supplied element is a {@link Method}.
* <p>Meta-annotations will be searched if the annotation is not
* <em>present</em> on the supplied element.
* @param annotatedElement the element to look for annotations on
* @param annotationType the annotation type to look for
* @param containerAnnotationType the type of the container that holds
* the annotations; may be {@code null} if a container is not supported
* or if it should be looked up via @{@link java.lang.annotation.Repeatable}
* when running on Java 8 or higher
* @return the annotations found or an empty set (never {@code null})
* @since 4.2
* @see #getRepeatableAnnotations(AnnotatedElement, Class)
* @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class)
* @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class, Class)
* @see AnnotatedElementUtils#getMergedRepeatableAnnotations(AnnotatedElement, Class, Class)
* @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
* @see java.lang.annotation.Repeatable
* @see java.lang.reflect.AnnotatedElement#getAnnotationsByType
*/
public static <A extends Annotation> Set<A> getRepeatableAnnotations(AnnotatedElement annotatedElement,
Class<A> annotationType, @Nullable Class<? extends Annotation> containerAnnotationType) {
Set<A> annotations = getDeclaredRepeatableAnnotations(annotatedElement, annotationType, containerAnnotationType);
if (!annotations.isEmpty()) {
return annotations;
}
if (annotatedElement instanceof Class) {
Class<?> superclass = ((Class<?>) annotatedElement).getSuperclass();
if (superclass != null && Object.class != superclass) {
return getRepeatableAnnotations(superclass, annotationType, containerAnnotationType);
}
}
return getRepeatableAnnotations(annotatedElement, annotationType, containerAnnotationType, false);
}
/**
* Get the declared <em>repeatable</em> {@linkplain Annotation annotations}
* of {@code annotationType} from the supplied {@link AnnotatedElement},
* where such annotations are either <em>directly present</em>,
* <em>indirectly present</em>, or <em>meta-present</em> on the element.
* <p>This method mimics the functionality of Java 8's
* {@link java.lang.reflect.AnnotatedElement#getDeclaredAnnotationsByType(Class)}
* with support for automatic detection of a <em>container annotation</em>
* declared via @{@link java.lang.annotation.Repeatable} (when running on
* Java 8 or higher) and with additional support for meta-annotations.
* <p>Handles both single annotations and annotations nested within a
* <em>container annotation</em>.
* <p>Correctly handles <em>bridge methods</em> generated by the
* compiler if the supplied element is a {@link Method}.
* <p>Meta-annotations will be searched if the annotation is not
* <em>present</em> on the supplied element.
* @param annotatedElement the element to look for annotations on
* @param annotationType the annotation type to look for
* @return the annotations found or an empty set (never {@code null})
* @since 4.2
* @see #getRepeatableAnnotations(AnnotatedElement, Class)
* @see #getRepeatableAnnotations(AnnotatedElement, Class, Class)
* @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class, Class)
* @see AnnotatedElementUtils#getMergedRepeatableAnnotations(AnnotatedElement, Class)
* @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
* @see java.lang.annotation.Repeatable
* @see java.lang.reflect.AnnotatedElement#getDeclaredAnnotationsByType
*/
public static <A extends Annotation> Set<A> getDeclaredRepeatableAnnotations(AnnotatedElement annotatedElement,
Class<A> annotationType) {
return getDeclaredRepeatableAnnotations(annotatedElement, annotationType, null);
}
/**
* Get the declared <em>repeatable</em> {@linkplain Annotation annotations}
* of {@code annotationType} from the supplied {@link AnnotatedElement},
* where such annotations are either <em>directly present</em>,
* <em>indirectly present</em>, or <em>meta-present</em> on the element.
* <p>This method mimics the functionality of Java 8's
* {@link java.lang.reflect.AnnotatedElement#getDeclaredAnnotationsByType(Class)}
* with additional support for meta-annotations.
* <p>Handles both single annotations and annotations nested within a
* <em>container annotation</em>.
* <p>Correctly handles <em>bridge methods</em> generated by the
* compiler if the supplied element is a {@link Method}.
* <p>Meta-annotations will be searched if the annotation is not
* <em>present</em> on the supplied element.
* @param annotatedElement the element to look for annotations on
* @param annotationType the annotation type to look for
* @param containerAnnotationType the type of the container that holds
* the annotations; may be {@code null} if a container is not supported
* or if it should be looked up via @{@link java.lang.annotation.Repeatable}
* when running on Java 8 or higher
* @return the annotations found or an empty set (never {@code null})
* @since 4.2
* @see #getRepeatableAnnotations(AnnotatedElement, Class)
* @see #getRepeatableAnnotations(AnnotatedElement, Class, Class)
* @see #getDeclaredRepeatableAnnotations(AnnotatedElement, Class)
* @see AnnotatedElementUtils#getMergedRepeatableAnnotations(AnnotatedElement, Class, Class)
* @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
* @see java.lang.annotation.Repeatable
* @see java.lang.reflect.AnnotatedElement#getDeclaredAnnotationsByType
*/
public static <A extends Annotation> Set<A> getDeclaredRepeatableAnnotations(AnnotatedElement annotatedElement,
Class<A> annotationType, @Nullable Class<? extends Annotation> containerAnnotationType) {
//得到一个set集合,看下面源码
return getRepeatableAnnotations(annotatedElement, annotationType, containerAnnotationType, true);
}
/**
* 最主要的实现是这个方法
* Perform the actual work for {@link #getRepeatableAnnotations(AnnotatedElement, Class, Class)}
* and {@link #getDeclaredRepeatableAnnotations(AnnotatedElement, Class, Class)}.
* <p>Correctly handles <em>bridge methods</em> generated by the
* compiler if the supplied element is a {@link Method}.
* <p>Meta-annotations will be searched if the annotation is not
* <em>present</em> on the supplied element.
* @param annotatedElement the element to look for annotations on
* @param annotationType the annotation type to look for
* @param containerAnnotationType the type of the container that holds
* the annotations; may be {@code null} if a container is not supported
* or if it should be looked up via @{@link java.lang.annotation.Repeatable}
* when running on Java 8 or higher
* @param declaredMode {@code true} if only declared annotations (i.e.,
* directly or indirectly present) should be considered
* @return the annotations found or an empty set (never {@code null})
* @since 4.2
* @see org.springframework.core.BridgeMethodResolver#findBridgedMethod
* @see java.lang.annotation.Repeatable
*/
private static <A extends Annotation> Set<A> getRepeatableAnnotations(AnnotatedElement annotatedElement,
Class<A> annotationType, @Nullable Class<? extends Annotation> containerAnnotationType, boolean declaredMode) {
Assert.notNull(annotatedElement, "AnnotatedElement must not be null");
Assert.notNull(annotationType, "Annotation type must not be null");
try {
if (annotatedElement instanceof Method) {
annotatedElement = BridgeMethodResolver.findBridgedMethod((Method) annotatedElement);
}
//返回的这个set集合包含的是要查找的注解及其被注解的元素,看下面源码
return new AnnotationCollector<>(annotationType, containerAnnotationType, declaredMode).getResult(annotatedElement);
}
catch (Throwable ex) {
handleIntrospectionFailure(annotatedElement, ex);
return Collections.emptySet();
}
}
...
private static class AnnotationCollector<A extends Annotation> {
private final Class<A> annotationType;
@Nullable
private final Class<? extends Annotation> containerAnnotationType;
private final boolean declaredMode;
private final Set<AnnotatedElement> visited = new HashSet<>();
private final Set<A> result = new LinkedHashSet<>();
AnnotationCollector(Class<A> annotationType,
@Nullable Class<? extends Annotation> containerAnnotationType, boolean declaredMode) {
this.annotationType = annotationType;
this.containerAnnotationType = (containerAnnotationType != null ? containerAnnotationType :
resolveContainerAnnotationType(annotationType));
this.declaredMode = declaredMode;
}
Set<A> getResult(AnnotatedElement element) {
process(element);
return Collections.unmodifiableSet(this.result);
}
@SuppressWarnings("unchecked")
private void process(AnnotatedElement element) {
if (this.visited.add(element)) {
try {
Annotation[] annotations = (this.declaredMode ? element.getDeclaredAnnotations() : element.getAnnotations());//从元素上得到注解
for (Annotation ann : annotations) {
Class<? extends Annotation> currentAnnotationType = ann.annotationType();
if (ObjectUtils.nullSafeEquals(this.annotationType, currentAnnotationType)) { //这个set集合添加的是要查找的注解及其被注解的元素
this.result.add(synthesizeAnnotation((A) ann, element));
}
else if (ObjectUtils.nullSafeEquals(this.containerAnnotationType, currentAnnotationType)) {
this.result.addAll(getValue(element, ann));
}
else if (!isInJavaLangAnnotationPackage(currentAnnotationType)) {
process(currentAnnotationType);
}
}
}
catch (Throwable ex) {
handleIntrospectionFailure(element, ex);
}
}
}
-
findAnnotation:通过传入
AnnotatedElement
和注解类型
来查找方法或者类对象上的注解。/** * Find a single {@link Annotation} of {@code annotationType} on the * supplied {@link AnnotatedElement}. * <p>Meta-annotations will be searched if the annotation is not * <em>directly present</em> on the supplied element. * <p><strong>Warning</strong>: this method operates generically on * annotated elements. In other words, this method does not execute * specialized search algorithms for classes or methods. If you require * the more specific semantics of {@link #findAnnotation(Class, Class)} * or {@link #findAnnotation(Method, Class)}, invoke one of those methods * instead. * @param annotatedElement the {@code AnnotatedElement} on which to find the annotation * @param annotationType the annotation type to look for, both locally and as a meta-annotation * @return the first matching annotation, or {@code null} if not found * @since 4.2 */ @Nullable public static <A extends Annotation> A findAnnotation(AnnotatedElement annotatedElement, Class<A> annotationType) { Assert.notNull(annotatedElement, "AnnotatedElement must not be null"); // Do NOT store result in the findAnnotationCache since doing so could break // findAnnotation(Class, Class) and findAnnotation(Method, Class). A ann = findAnnotation(annotatedElement, annotationType, new HashSet<>()); return (ann != null ? synthesizeAnnotation(ann, annotatedElement) : null); } /** * Perform the search algorithm for {@link #findAnnotation(AnnotatedElement, Class)} * avoiding endless recursion by tracking which annotations have already * been <em>visited</em>. * @param annotatedElement the {@code AnnotatedElement} on which to find the annotation * @param annotationType the annotation type to look for, both locally and as a meta-annotation * @param visited the set of annotations that have already been visited * @return the first matching annotation, or {@code null} if not found * @since 4.2 */ @Nullable private static <A extends Annotation> A findAnnotation( AnnotatedElement annotatedElement, Class<A> annotationType, Set<Annotation> visited) { try { A annotation = annotatedElement.getDeclaredAnnotation(annotationType); if (annotation != null) { return annotation; } for (Annotation declaredAnn : annotatedElement.getDeclaredAnnotations()) { Class<? extends Annotation> declaredType = declaredAnn.annotationType(); if (!isInJavaLangAnnotationPackage(declaredType) && visited.add(declaredAnn)) { annotation = findAnnotation((AnnotatedElement) declaredType, annotationType, visited); if (annotation != null) { return annotation; } } } } catch (Throwable ex) { handleIntrospectionFailure(annotatedElement, ex); } return null; }
-
isAnnotationDeclaredLocally:检查注解是否在类中本地声明,而不是继承。
/**
* Determine whether an annotation of the specified {@code annotationType}
* is declared locally (i.e., <em>directly present</em>) on the supplied
* {@code clazz}.
* <p>The supplied {@link Class} may represent any type.
* <p>Meta-annotations will <em>not</em> be searched.
* <p>Note: This method does <strong>not</strong> determine if the annotation
* is {@linkplain java.lang.annotation.Inherited inherited}. For greater
* clarity regarding inherited annotations, consider using
* {@link #isAnnotationInherited(Class, Class)} instead.
* @param annotationType the annotation type to look for
* @param clazz the class to check for the annotation on
* @return {@code true} if an annotation of the specified {@code annotationType}
* is <em>directly present</em>
* @see java.lang.Class#getDeclaredAnnotations()
* @see java.lang.Class#getDeclaredAnnotation(Class)
* @see #isAnnotationInherited(Class, Class)
*/
public static boolean isAnnotationDeclaredLocally(Class<? extends Annotation> annotationType, Class<?> clazz) {
Assert.notNull(annotationType, "Annotation type must not be null");
Assert.notNull(clazz, "Class must not be null");
try {
return (clazz.getDeclaredAnnotation(annotationType) != null);
}
catch (Throwable ex) {
handleIntrospectionFailure(clazz, ex);
return false;
}
}
- isAnnotationInherited:检查注解是否从另一个类继承(即未在本地声明)。
/**
* Determine whether an annotation of the specified {@code annotationType}
* is <em>present</em> on the supplied {@code clazz} and is
* {@linkplain java.lang.annotation.Inherited inherited} (i.e., not
* <em>directly present</em>).
* <p>Meta-annotations will <em>not</em> be searched.
* <p>If the supplied {@code clazz} is an interface, only the interface
* itself will be checked. In accordance with standard meta-annotation
* semantics in Java, the inheritance hierarchy for interfaces will not
* be traversed. See the {@linkplain java.lang.annotation.Inherited javadoc}
* for the {@code @Inherited} meta-annotation for further details regarding
* annotation inheritance.
* @param annotationType the annotation type to look for
* @param clazz the class to check for the annotation on
* @return {@code true} if an annotation of the specified {@code annotationType}
* is <em>present</em> and <em>inherited</em>
* @see Class#isAnnotationPresent(Class)
* @see #isAnnotationDeclaredLocally(Class, Class)
*/
public static boolean isAnnotationInherited(Class<? extends Annotation> annotationType, Class<?> clazz) {
Assert.notNull(annotationType, "Annotation type must not be null");
Assert.notNull(clazz, "Class must not be null");
return (clazz.isAnnotationPresent(annotationType) && !isAnnotationDeclaredLocally(annotationType, clazz));
}
- getAnnotationAttributes:获取给定注解的属性。
/**
* Retrieve the given annotation's attributes as a {@link Map}, preserving all
* attribute types.
* <p>Equivalent to calling {@link #getAnnotationAttributes(Annotation, boolean, boolean)}
* with the {@code classValuesAsString} and {@code nestedAnnotationsAsMap} parameters
* set to {@code false}.
* <p>Note: This method actually returns an {@link AnnotationAttributes} instance.
* However, the {@code Map} signature has been preserved for binary compatibility.
* @param annotation the annotation to retrieve the attributes for
* @return the Map of annotation attributes, with attribute names as keys and
* corresponding attribute values as values (never {@code null})
* @see #getAnnotationAttributes(AnnotatedElement, Annotation)
* @see #getAnnotationAttributes(Annotation, boolean, boolean)
* @see #getAnnotationAttributes(AnnotatedElement, Annotation, boolean, boolean)
*/
public static Map<String, Object> getAnnotationAttributes(Annotation annotation) {
return getAnnotationAttributes(null, annotation);
}
/**
* Retrieve the given annotation's attributes as a {@link Map}.
* <p>Equivalent to calling {@link #getAnnotationAttributes(Annotation, boolean, boolean)}
* with the {@code nestedAnnotationsAsMap} parameter set to {@code false}.
* <p>Note: This method actually returns an {@link AnnotationAttributes} instance.
* However, the {@code Map} signature has been preserved for binary compatibility.
* @param annotation the annotation to retrieve the attributes for
* @param classValuesAsString whether to convert Class references into Strings (for
* compatibility with {@link org.springframework.core.type.AnnotationMetadata})
* or to preserve them as Class references
* @return the Map of annotation attributes, with attribute names as keys and
* corresponding attribute values as values (never {@code null})
* @see #getAnnotationAttributes(Annotation, boolean, boolean)
*/
public static Map<String, Object> getAnnotationAttributes(Annotation annotation, boolean classValuesAsString) {
return getAnnotationAttributes(annotation, classValuesAsString, false);
}
/**
* Retrieve the given annotation's attributes as an {@link AnnotationAttributes} map.
* <p>This method provides fully recursive annotation reading capabilities on par with
* the reflection-based {@link org.springframework.core.type.StandardAnnotationMetadata}.
* @param annotation the annotation to retrieve the attributes for
* @param classValuesAsString whether to convert Class references into Strings (for
* compatibility with {@link org.springframework.core.type.AnnotationMetadata})
* or to preserve them as Class references
* @param nestedAnnotationsAsMap whether to convert nested annotations into
* {@link AnnotationAttributes} maps (for compatibility with
* {@link org.springframework.core.type.AnnotationMetadata}) or to preserve them as
* {@code Annotation} instances
* @return the annotation attributes (a specialized Map) with attribute names as keys
* and corresponding attribute values as values (never {@code null})
* @since 3.1.1
*/
public static AnnotationAttributes getAnnotationAttributes(Annotation annotation, boolean classValuesAsString,
boolean nestedAnnotationsAsMap) {
return getAnnotationAttributes(null, annotation, classValuesAsString, nestedAnnotationsAsMap);
}
/**
* Retrieve the given annotation's attributes as an {@link AnnotationAttributes} map.
* <p>Equivalent to calling {@link #getAnnotationAttributes(AnnotatedElement, Annotation, boolean, boolean)}
* with the {@code classValuesAsString} and {@code nestedAnnotationsAsMap} parameters
* set to {@code false}.
* @param annotatedElement the element that is annotated with the supplied annotation;
* may be {@code null} if unknown
* @param annotation the annotation to retrieve the attributes for
* @return the annotation attributes (a specialized Map) with attribute names as keys
* and corresponding attribute values as values (never {@code null})
* @since 4.2
* @see #getAnnotationAttributes(AnnotatedElement, Annotation, boolean, boolean)
*/
public static AnnotationAttributes getAnnotationAttributes(@Nullable AnnotatedElement annotatedElement, Annotation annotation) {
return getAnnotationAttributes(annotatedElement, annotation, false, false);
}
/**
* Retrieve the given annotation's attributes as an {@link AnnotationAttributes} map.
* <p>This method provides fully recursive annotation reading capabilities on par with
* the reflection-based {@link org.springframework.core.type.StandardAnnotationMetadata}.
* @param annotatedElement the element that is annotated with the supplied annotation;
* may be {@code null} if unknown
* @param annotation the annotation to retrieve the attributes for
* @param classValuesAsString whether to convert Class references into Strings (for
* compatibility with {@link org.springframework.core.type.AnnotationMetadata})
* or to preserve them as Class references
* @param nestedAnnotationsAsMap whether to convert nested annotations into
* {@link AnnotationAttributes} maps (for compatibility with
* {@link org.springframework.core.type.AnnotationMetadata}) or to preserve them as
* {@code Annotation} instances
* @return the annotation attributes (a specialized Map) with attribute names as keys
* and corresponding attribute values as values (never {@code null})
* @since 4.2
*/
public static AnnotationAttributes getAnnotationAttributes(@Nullable AnnotatedElement annotatedElement,
Annotation annotation, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
return getAnnotationAttributes(
(Object) annotatedElement, annotation, classValuesAsString, nestedAnnotationsAsMap);
}
private static AnnotationAttributes getAnnotationAttributes(@Nullable Object annotatedElement,
Annotation annotation, boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
AnnotationAttributes attributes =
retrieveAnnotationAttributes(annotatedElement, annotation, classValuesAsString, nestedAnnotationsAsMap);
postProcessAnnotationAttributes(annotatedElement, attributes, classValuesAsString, nestedAnnotationsAsMap);
return attributes;
}
/**
* Retrieve the given annotation's attributes as an {@link AnnotationAttributes} map.
* <p>This method provides fully recursive annotation reading capabilities on par with
* the reflection-based {@link org.springframework.core.type.StandardAnnotationMetadata}.
* <p><strong>NOTE</strong>: This variant of {@code getAnnotationAttributes()} is
* only intended for use within the framework. The following special rules apply:
* <ol>
* <li>Default values will be replaced with default value placeholders.</li>
* <li>The resulting, merged annotation attributes should eventually be
* {@linkplain #postProcessAnnotationAttributes post-processed} in order to
* ensure that placeholders have been replaced by actual default values and
* in order to enforce {@code @AliasFor} semantics.</li>
* </ol>
* @param annotatedElement the element that is annotated with the supplied annotation;
* may be {@code null} if unknown
* @param annotation the annotation to retrieve the attributes for
* @param classValuesAsString whether to convert Class references into Strings (for
* compatibility with {@link org.springframework.core.type.AnnotationMetadata})
* or to preserve them as Class references
* @param nestedAnnotationsAsMap whether to convert nested annotations into
* {@link AnnotationAttributes} maps (for compatibility with
* {@link org.springframework.core.type.AnnotationMetadata}) or to preserve them as
* {@code Annotation} instances
* @return the annotation attributes (a specialized Map) with attribute names as keys
* and corresponding attribute values as values (never {@code null})
* @since 4.2
* @see #postProcessAnnotationAttributes
*/
static AnnotationAttributes retrieveAnnotationAttributes(@Nullable Object annotatedElement, Annotation annotation,
boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
Class<? extends Annotation> annotationType = annotation.annotationType();
AnnotationAttributes attributes = new AnnotationAttributes(annotationType);
for (Method method : getAttributeMethods(annotationType)) {
try {
Object attributeValue = method.invoke(annotation);
Object defaultValue = method.getDefaultValue();
if (defaultValue != null && ObjectUtils.nullSafeEquals(attributeValue, defaultValue)) {
attributeValue = new DefaultValueHolder(defaultValue);
}
attributes.put(method.getName(),
adaptValue(annotatedElement, attributeValue, classValuesAsString, nestedAnnotationsAsMap));
}
catch (Throwable ex) {
if (ex instanceof InvocationTargetException) {
Throwable targetException = ((InvocationTargetException) ex).getTargetException();
rethrowAnnotationConfigurationException(targetException);
}
throw new IllegalStateException("Could not obtain annotation attribute value for " + method, ex);
}
}
return attributes;
}
/**
* Adapt the given value according to the given class and nested annotation settings.
* <p>Nested annotations will be
* {@linkplain #synthesizeAnnotation(Annotation, AnnotatedElement) synthesized}.
* @param annotatedElement the element that is annotated, used for contextual
* logging; may be {@code null} if unknown
* @param value the annotation attribute value
* @param classValuesAsString whether to convert Class references into Strings (for
* compatibility with {@link org.springframework.core.type.AnnotationMetadata})
* or to preserve them as Class references
* @param nestedAnnotationsAsMap whether to convert nested annotations into
* {@link AnnotationAttributes} maps (for compatibility with
* {@link org.springframework.core.type.AnnotationMetadata}) or to preserve them as
* {@code Annotation} instances
* @return the adapted value, or the original value if no adaptation is needed
*/
@Nullable
static Object adaptValue(@Nullable Object annotatedElement, @Nullable Object value,
boolean classValuesAsString, boolean nestedAnnotationsAsMap) {
if (classValuesAsString) {
if (value instanceof Class) {
return ((Class<?>) value).getName();
}
else if (value instanceof Class[]) {
Class<?>[] clazzArray = (Class<?>[]) value;
String[] classNames = new String[clazzArray.length];
for (int i = 0; i < clazzArray.length; i++) {
classNames[i] = clazzArray[i].getName();
}
return classNames;
}
}
if (value instanceof Annotation) {
Annotation annotation = (Annotation) value;
if (nestedAnnotationsAsMap) {
return getAnnotationAttributes(annotatedElement, annotation, classValuesAsString, true);
}
else {
return synthesizeAnnotation(annotation, annotatedElement);
}
}
if (value instanceof Annotation[]) {
Annotation[] annotations = (Annotation[]) value;
if (nestedAnnotationsAsMap) {
AnnotationAttributes[] mappedAnnotations = new AnnotationAttributes[annotations.length];
for (int i = 0; i < annotations.length; i++) {
mappedAnnotations[i] =
getAnnotationAttributes(annotatedElement, annotations[i], classValuesAsString, true);
}
return mappedAnnotations;
}
else {
return synthesizeAnnotationArray(annotations, annotatedElement);
}
}
// Fallback
return value;
}
- getValue:获取给定注解的值。 有这个名称的存在两种方法。第一个返回注解的全局值。第二个是指定注解参数的值。
/**
* Retrieve the <em>value</em> of the {@code value} attribute of a
* single-element Annotation, given an annotation instance.
* @param annotation the annotation instance from which to retrieve the value
* @return the attribute value, or {@code null} if not found unless the attribute
* value cannot be retrieved due to an {@link AnnotationConfigurationException},
* in which case such an exception will be rethrown
* @see #getValue(Annotation, String)
*/
@Nullable
public static Object getValue(Annotation annotation) {
return getValue(annotation, VALUE);
}
/**
* Retrieve the <em>value</em> of a named attribute, given an annotation instance.
* @param annotation the annotation instance from which to retrieve the value
* @param attributeName the name of the attribute value to retrieve
* @return the attribute value, or {@code null} if not found unless the attribute
* value cannot be retrieved due to an {@link AnnotationConfigurationException},
* in which case such an exception will be rethrown
* @see #getValue(Annotation)
* @see #rethrowAnnotationConfigurationException(Throwable)
*/
@Nullable
public static Object getValue(@Nullable Annotation annotation, @Nullable String attributeName) {
if (annotation == null || !StringUtils.hasText(attributeName)) {
return null;
}
try {
Method method = annotation.annotationType().getDeclaredMethod(attributeName);
ReflectionUtils.makeAccessible(method);
return method.invoke(annotation);
}
catch (InvocationTargetException ex) {
rethrowAnnotationConfigurationException(ex.getTargetException());
throw new IllegalStateException(
"Could not obtain value for annotation attribute '" + attributeName + "' in " + annotation, ex);
}
catch (Throwable ex) {
handleIntrospectionFailure(annotation.getClass(), ex);
return null;
}
}
- getDefaultValue:获取给定注解或注解属性的默认值(注意
@Nullable
注解就知道为什么这么说了)。
/**
* Retrieve the <em>default value</em> of the {@code value} attribute
* of a single-element Annotation, given an annotation instance.
* @param annotation the annotation instance from which to retrieve the default value
* @return the default value, or {@code null} if not found
* @see #getDefaultValue(Annotation, String)
*/
@Nullable
public static Object getDefaultValue(Annotation annotation) {
return getDefaultValue(annotation, VALUE);
}
/**
* Retrieve the <em>default value</em> of a named attribute, given an annotation instance.
* @param annotation the annotation instance from which to retrieve the default value
* @param attributeName the name of the attribute value to retrieve
* @return the default value of the named attribute, or {@code null} if not found
* @see #getDefaultValue(Class, String)
*/
@Nullable
public static Object getDefaultValue(@Nullable Annotation annotation, @Nullable String attributeName) {
if (annotation == null) {
return null;
}
return getDefaultValue(annotation.annotationType(), attributeName);
}
/**
* Retrieve the <em>default value</em> of the {@code value} attribute
* of a single-element Annotation, given the {@link Class annotation type}.
* @param annotationType the <em>annotation type</em> for which the default value should be retrieved
* @return the default value, or {@code null} if not found
* @see #getDefaultValue(Class, String)
*/
@Nullable
public static Object getDefaultValue(Class<? extends Annotation> annotationType) {
return getDefaultValue(annotationType, VALUE);
}
/**
* Retrieve the <em>default value</em> of a named attribute, given the
* {@link Class annotation type}.
* @param annotationType the <em>annotation type</em> for which the default value should be retrieved
* @param attributeName the name of the attribute value to retrieve.
* @return the default value of the named attribute, or {@code null} if not found
* @see #getDefaultValue(Annotation, String)
*/
@Nullable
public static Object getDefaultValue(
@Nullable Class<? extends Annotation> annotationType, @Nullable String attributeName) {
if (annotationType == null || !StringUtils.hasText(attributeName)) {
return null;
}
try {
return annotationType.getDeclaredMethod(attributeName).getDefaultValue();
}
catch (Throwable ex) {
handleIntrospectionFailure(annotationType, ex);
return null;
}
}
有哪些地方使用了AnnotationUtils方法?
很多Spring项目模块都用了AnnotationUtils
。这里我们将重点关注与core
和Web开发相关的项目模块:Web
,Web MVC
,context
和bean
。这里就不罗嗦太多了,只列出在这些Spring项目中使用的AnnotationUtils
的地方:
-
web MVC
AnnotationMethodHandlerAdapter
,直到 Spring 3.1的版本都是作为注解方法的主要处理程序,使用AnnotationUtils
来检查可用于方法级别的不同注解,如:@RequestMapping
,@ResponseStatus
,@ResponseBody
或@ModelAttribute
。- 作为
AnnotationMethodHandlerAdapter
接班人,RequestMappingHandlerMapping
与AnnotationUtils
一起解析@RequestMapping
并构造了封装映射配置(变量,HTTP方法, accepted headers 等)的RequestMappingInfo
对象。
/** * Uses method and type-level @{@link RequestMapping} annotations to create * the RequestMappingInfo. * @return the created RequestMappingInfo, or {@code null} if the method * does not have a {@code @RequestMapping} annotation. * @see #getCustomMethodCondition(Method) * @see #getCustomTypeCondition(Class) */ @Override protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) { RequestMappingInfo info = createRequestMappingInfo(method); if (info != null) { RequestMappingInfo typeInfo = createRequestMappingInfo(handlerType); if (typeInfo != null) { info = typeInfo.combine(info); } } return info; } /** * Delegates to {@link #createRequestMappingInfo(RequestMapping, RequestCondition)}, * supplying the appropriate custom {@link RequestCondition} depending on whether * the supplied {@code annotatedElement} is a class or method. * @see #getCustomTypeCondition(Class) * @see #getCustomMethodCondition(Method) */ private RequestMappingInfo createRequestMappingInfo(AnnotatedElement element) { RequestMapping requestMapping = AnnotatedElementUtils.findMergedAnnotation(element, RequestMapping.class); RequestCondition<?> condition = (element instanceof Class ? getCustomTypeCondition((Class<?>) element) : getCustomMethodCondition((Method) element)); return (requestMapping != null ? createRequestMappingInfo(requestMapping, condition) : null); }
RequestMappingHandlerAdapter
是Web MVC
项目中使用AnnotationUtils
的第三个重要类。我们可以找到2个调用了findAnnotation()
方法并都返回MethodFilter
类的实例的方法。一个表示@InitBinder
注解,第一个表示@ModelAttribute
。
/** * MethodFilter that matches {@link InitBinder @InitBinder} methods. */ public static final MethodFilter INIT_BINDER_METHODS = method -> AnnotationUtils.findAnnotation(method, InitBinder.class) != null; /** * MethodFilter that matches {@link ModelAttribute @ModelAttribute} methods. */ public static final MethodFilter MODEL_ATTRIBUTE_METHODS = method -> ((AnnotationUtils.findAnnotation(method, RequestMapping.class) == null) && (AnnotationUtils.findAnnotation(method, ModelAttribute.class) != null)); //以上两个方法的用法 private void initControllerAdviceCache() { if (getApplicationContext() == null) { return; } if (logger.isInfoEnabled()) { logger.info("Looking for @ControllerAdvice: " + getApplicationContext()); } List<ControllerAdviceBean> beans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext()); AnnotationAwareOrderComparator.sort(beans); List<Object> requestResponseBodyAdviceBeans = new ArrayList<Object>(); for (ControllerAdviceBean bean : beans) { //传入MODEL_ATTRIBUTE_METHODS这个表达式 Set<Method> attrMethods = MethodIntrospector.selectMethods(bean.getBeanType(), MODEL_ATTRIBUTE_METHODS); if (!attrMethods.isEmpty()) { this.modelAttributeAdviceCache.put(bean, attrMethods); if (logger.isInfoEnabled()) { logger.info("Detected @ModelAttribute methods in " + bean); } } //传入 INIT_BINDER_METHODS 这个表达式 Set<Method> binderMethods = MethodIntrospector.selectMethods(bean.getBeanType(), INIT_BINDER_METHODS); if (!binderMethods.isEmpty()) { this.initBinderAdviceCache.put(bean, binderMethods); if (logger.isInfoEnabled()) { logger.info("Detected @InitBinder methods in " + bean); } } if (RequestBodyAdvice.class.isAssignableFrom(bean.getBeanType())) { requestResponseBodyAdviceBeans.add(bean); if (logger.isInfoEnabled()) { logger.info("Detected RequestBodyAdvice bean in " + bean); } } if (ResponseBodyAdvice.class.isAssignableFrom(bean.getBeanType())) { requestResponseBodyAdviceBeans.add(bean); if (logger.isInfoEnabled()) { logger.info("Detected ResponseBodyAdvice bean in " + bean); } } } if (!requestResponseBodyAdviceBeans.isEmpty()) { this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans); } }
接上面最后一个方法selectMethods
的实现,然后,我们平时写代码的时候也可以参考此实现形式:
org.springframework.core.MethodIntrospector
/**
* Select methods on the given target type based on a filter.
* <p>Callers define methods of interest through the {@code MethodFilter} parameter.
* @param targetType the target type to search methods on
* @param methodFilter a {@code MethodFilter} to help
* recognize handler methods of interest
* @return the selected methods, or an empty set in case of no match
*/
public static Set<Method> selectMethods(Class<?> targetType, final ReflectionUtils.MethodFilter methodFilter) {
return selectMethods(targetType, new MetadataLookup<Boolean>() {
@Override
public Boolean inspect(Method method) {
return (methodFilter.matches(method) ? Boolean.TRUE : null);
}
}).keySet();
}
//此段代码可迭代为下面形式,这样更加符合之前定义methodFilter的习惯
public static Set<Method> selectMethods(Class<?> targetType, final ReflectionUtils.MethodFilter methodFilter) {
return selectMethods(targetType, (MetadataLookup)(method)-> {
return (methodFilter.matches(method) ? Boolean.TRUE : null);
}).keySet();
}
-
web(此处分析俩过时的类,Spring5里没有,但是4里面包含有,之前的文章有写)
- 如果对象必须使用
@Valid
进行验证,或者@InitBinder
方法存在,HandlerMethodInvoker
使用AnnotationUtils
来知道@ModelAttribute
注解是什么。 - 这个项目的另一个关键类,
HandlerMethodResolver
,通过调用AnnotationUtils
方法来确定方法的类型(handler,binder或model-attribute)。具体点讲就是通过3种方法完成:isHandlerMethod
,isInitBinderMethod
和isModelAttributeMethod
。每个都接受Method的实例为参数。
- 如果对象必须使用
-
context
- 用于解析bean注解的类
BeanAnnotationHelper
使用AnnotationUtils
中的findMergedAnnotation()
方法来处理用@Bean
注解的类。我们使用它来确定bean的名称。
/** * Utilities for processing {@link Bean}-annotated methods. * * @author Chris Beams * @author Juergen Hoeller * @since 3.1 */ class BeanAnnotationHelper { public static boolean isBeanAnnotated(Method method) { return AnnotatedElementUtils.hasAnnotation(method, Bean.class); } public static String determineBeanNameFor(Method beanMethod) { // By default, the bean name is the name of the @Bean-annotated method String beanName = beanMethod.getName(); // Check to see if the user has explicitly set a custom bean name... Bean bean = AnnotatedElementUtils.findMergedAnnotation(beanMethod, Bean.class); if (bean != null && bean.name().length > 0) { beanName = bean.name()[0]; } return beanName; } }
- 还有一个要说的就是
AnnotationAsyncExecutionInterceptor
类,其内同样使用AnnotationUtils
来解析注解。它调用findMergedAnnotation()
方法来解析在运行时所执行的方法的名称。
/** * Specialization of {@link AsyncExecutionInterceptor} that delegates method execution to * an {@code Executor} based on the {@link Async} annotation. Specifically designed to * support use of {@link Async#value()} executor qualification mechanism introduced in * Spring 3.1.2. Supports detecting qualifier metadata via {@code @Async} at the method or * declaring class level. See {@link #getExecutorQualifier(Method)} for details. * * @author Chris Beams * @author Stephane Nicoll * @since 3.1.2 * @see org.springframework.scheduling.annotation.Async * @see org.springframework.scheduling.annotation.AsyncAnnotationAdvisor */ public class AnnotationAsyncExecutionInterceptor extends AsyncExecutionInterceptor { /** * Create a new {@code AnnotationAsyncExecutionInterceptor} with the given executor * and a simple {@link AsyncUncaughtExceptionHandler}. * @param defaultExecutor the executor to be used by default if no more specific * executor has been qualified at the method level using {@link Async#value()}; * as of 4.2.6, a local executor for this interceptor will be built otherwise */ public AnnotationAsyncExecutionInterceptor(@Nullable Executor defaultExecutor) { super(defaultExecutor); } /** * Create a new {@code AnnotationAsyncExecutionInterceptor} with the given executor. * @param defaultExecutor the executor to be used by default if no more specific * executor has been qualified at the method level using {@link Async#value()}; * as of 4.2.6, a local executor for this interceptor will be built otherwise * @param exceptionHandler the {@link AsyncUncaughtExceptionHandler} to use to * handle exceptions thrown by asynchronous method executions with {@code void} * return type */ public AnnotationAsyncExecutionInterceptor(@Nullable Executor defaultExecutor, AsyncUncaughtExceptionHandler exceptionHandler) { super(defaultExecutor, exceptionHandler); } /** * Return the qualifier or bean name of the executor to be used when executing the * given method, specified via {@link Async#value} at the method or declaring * class level. If {@code @Async} is specified at both the method and class level, the * method's {@code #value} takes precedence (even if empty string, indicating that * the default executor should be used preferentially). * @param method the method to inspect for executor qualifier metadata * @return the qualifier if specified, otherwise empty string indicating that the * {@linkplain #setExecutor(Executor) default executor} should be used * @see #determineAsyncExecutor(Method) */ @Override protected String getExecutorQualifier(Method method) { // Maintainer's note: changes made here should also be made in // AnnotationAsyncExecutionAspect#getExecutorQualifier Async async = AnnotatedElementUtils.findMergedAnnotation(method, Async.class); if (async == null) { async = AnnotatedElementUtils.findMergedAnnotation(method.getDeclaringClass(), Async.class); } return (async != null ? async.value() : null); } }
- 用于解析bean注解的类
-
bean
- 我们可以在
StaticListableBeanFactory
或DefaultListableBeanFactory
类中找到AnnotationUtils
用来查找bean
的注解的用法。
org.springframework.beans.factory.support.StaticListableBeanFactory
@Override public Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType) throws BeansException { Map<String, Object> results = new LinkedHashMap<>(); for (String beanName : this.beans.keySet()) { if (findAnnotationOnBean(beanName, annotationType) != null) { results.put(beanName, getBean(beanName)); } } return results; } @Override public <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType) throws NoSuchBeanDefinitionException{ Class<?> beanType = getType(beanName); return (beanType != null ? AnnotationUtils.findAnnotation(beanType, annotationType) : null); }
org.springframework.beans.factory.support.DefaultListableBeanFactory
@Override public String[] getBeanNamesForAnnotation(Class<? extends Annotation> annotationType) { List<String> results = new ArrayList<>(); for (String beanName : this.beanDefinitionNames) { BeanDefinition beanDefinition = getBeanDefinition(beanName); if (!beanDefinition.isAbstract() && findAnnotationOnBean(beanName, annotationType) != null) { results.add(beanName); } } for (String beanName : this.manualSingletonNames) { if (!results.contains(beanName) && findAnnotationOnBean(beanName, annotationType) != null) { results.add(beanName); } } return results.toArray(new String[results.size()]); } @Override public Map<String, Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType) { String[] beanNames = getBeanNamesForAnnotation(annotationType); Map<String, Object> results = new LinkedHashMap<>(beanNames.length); for (String beanName : beanNames) { results.put(beanName, getBean(beanName)); } return results; } /** * Find a {@link Annotation} of {@code annotationType} on the specified * bean, traversing its interfaces and super classes if no annotation can be * found on the given class itself, as well as checking its raw bean class * if not found on the exposed bean reference (e.g. in case of a proxy). */ @Override public <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType) throws NoSuchBeanDefinitionException{ A ann = null; Class<?> beanType = getType(beanName); if (beanType != null) { ann = AnnotationUtils.findAnnotation(beanType, annotationType); } if (ann == null && containsBeanDefinition(beanName)) { BeanDefinition bd = getMergedBeanDefinition(beanName); if (bd instanceof AbstractBeanDefinition) { AbstractBeanDefinition abd = (AbstractBeanDefinition) bd; if (abd.hasBeanClass()) { ann = AnnotationUtils.findAnnotation(abd.getBeanClass(), annotationType); } } } return ann; }
- 我们可以在
AnnotationUtils in Action
为了更好地理解Spring中AnnotationUtils的工作方式,我们来搞两个注解:第一个对应方法,第二个对应类。之后,写两个测试类和一个playground
类,我们要达到的目的是输出由AnnotationUtils
完成的注解分析结果。这两个注解定义如下:
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface ClassNameAnnotation {
String className() default "Empty class name";
}
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface StaticTextAnnotation {
String text() default "Default text for static text annotation";
String value() default "Default value";
}
@Retention注解是必需的(估计这里是大家的知识盲区,所以特地点出来)。否则AnnotationUtils将无法检测到这些注解。注意在StaticTextAnnotation
中存在value()
属性,并且在ClassNameAnnotation
中不存在此属性。在以下代码中,你可以找到相应的测试类:
@ClassNameAnnotation(className = "TestChildren")
public class TestParent {
@StaticTextAnnotation(value= "Custom text value", text = "Test text")
public String test(HttpServletRequest request) {
return "test";
}
}
public class TestChildren extends TestParent {
}
TestChildren
类没有任何注解。我们使用它来测试继承注解检查。
public class Playground {
public static void main(String[] args) {
try {
Method method = TestParent.class.getMethod("test", new Class[]{HttpServletRequest.class});
Annotation staticTextAnnot = AnnotationUtils.findAnnotation(method, StaticTextAnnotation.class);
System.out.println("@StaticTextAnnotation of method is: "+staticTextAnnot);
System.out.println("@StaticTextAnnotation method value: "+AnnotationUtils.getValue(staticTextAnnot, "text"));
System.out.println("@StaticTextAnnotation method default value: "+AnnotationUtils.getDefaultValue(staticTextAnnot, "text"));
System.out.println("@StaticTextAnnotation value: "+AnnotationUtils.getValue(staticTextAnnot));
// inheriting annotations tests
Annotation classNameAnnotation = AnnotationUtils.findAnnotation(TestChildren.class, ClassNameAnnotation.class);
System.out.println("@ClassNameAnnotation of TestChildren.class is: "+classNameAnnotation);
System.out.println("@ClassNameAnnotation method value: "+AnnotationUtils.getValue(classNameAnnotation, "className"));
System.out.println("@ClassNameAnnotation method default value: "+AnnotationUtils.getDefaultValue(classNameAnnotation, "className"));
System.out.println("@ClassNameAnnotation value: "+AnnotationUtils.getValue(classNameAnnotation));
} catch (Exception e) {
e.printStackTrace();
}
}
}
Playground
的main
方法结果如下:
@StaticTextAnnotation of method is: @com.migo.annotations.StaticTextAnnotation(text=Test text, value=Custom text value)
@StaticTextAnnotation method value: Test text
@StaticTextAnnotation method default value: Default text for static text annotation
@StaticTextAnnotation value: Custom text value
@ClassNameAnnotation of TestChildren.class is: @com.migo.annotations.ClassNameAnnotation(className=TestChildren)
@ClassNameAnnotation method value: TestChildren
@ClassNameAnnotation method default value: Empty class name
@ClassNameAnnotation value: null
如上所示,我们可以很轻易的了解很多注解点。我们可以检查value()
属性或另一个自定义属性的值。我们还可以检查属性的默认值。除此之外,AnnotationUtils
还可以在继承体系结构中进行注解操作。