作用

按照我的理解AnnotationAttributes是为了存储注解属性或者信息的，可以通过org.springframework.core.annotation.AnnotationUtils.getAnnotationAttributes(annotation);得到
比如：

@ComponentScan
public class Math {public static void main(String[] args) {Annotation annotation= Math.class.getAnnotation(ComponentScan.class);System.out.println("annotationType=>"+annotation.annotationType());AnnotationAttributes ComponentScanAnnotationAttributes= (AnnotationAttributes) AnnotationUtils.getAnnotationAttributes(annotation);ComponentScanAnnotationAttributes.forEach((key,value) ->{System.out.println(key+"=>"+value);});//如果不强转，就直接得到了MapMap<String,Object> map=AnnotationUtils.getAnnotationAttributes(annotation);Set<String> set=map.keySet();for(String key:set){System.out.println(key+"=>"+map.get(key));}}
}
输出如下
annotationType=>interface org.springframework.context.annotation.ComponentScan
basePackageClasses=>[Ljava.lang.Class;@1563da5
basePackages=>[Ljava.lang.String;@2bbf4b8b
excludeFilters=>[Lorg.springframework.context.annotation.ComponentScan$Filter;@30a3107a
includeFilters=>[Lorg.springframework.context.annotation.ComponentScan$Filter;@33c7e1bb
lazyInit=>false
nameGenerator=>interface org.springframework.beans.factory.support.BeanNameGenerator
resourcePattern=>**/*.class
scopeResolver=>class org.springframework.context.annotation.AnnotationScopeMetadataResolver
scopedProxy=>DEFAULT
useDefaultFilters=>true
value=>[Ljava.lang.String;@2bbf4b8b
SimpleName=>BeanNameGenerator

当然也可以获取注解的注解

构造函数以及成员

public class AnnotationAttributes extends LinkedHashMap<String, Object> {private static final String UNKNOWN = "unknown";//表示注解类型@Nullableprivate final Class<? extends Annotation> annotationType;//未知final String displayName;boolean validated = false;public AnnotationAttributes() {this.annotationType = null;this.displayName = UNKNOWN;}/*AnnotationAttributes 继承了LinkedHashMap，所以这个构造方法通过initialCapacity初始化指定容量的空间*/public AnnotationAttributes(int initialCapacity) {super(initialCapacity);this.annotationType = null;this.displayName = UNKNOWN;}public AnnotationAttributes(Map<String, Object> map) {super(map);this.annotationType = null;this.displayName = UNKNOWN;}public AnnotationAttributes(AnnotationAttributes other) {super(other);this.annotationType = other.annotationType;this.displayName = other.displayName;this.validated = other.validated;}public AnnotationAttributes(Class<? extends Annotation> annotationType) {Assert.notNull(annotationType, "'annotationType' must not be null");this.annotationType = annotationType;this.displayName = annotationType.getName();}AnnotationAttributes(Class<? extends Annotation> annotationType, boolean validated) {Assert.notNull(annotationType, "'annotationType' must not be null");this.annotationType = annotationType;this.displayName = annotationType.getName();this.validated = validated;}public AnnotationAttributes(String annotationType, @Nullable ClassLoader classLoader)               {Assert.notNull(annotationType, "'annotationType' must not be null");this.annotationType = getAnnotationType(annotationType, classLoader);this.displayName = annotationType;}
}

可以看到，AnnotationAttributes 继承了LinkedHashMap，我们可以像遍历map那样遍历它，如文章开头代码。

主要方法

 /**得到注解类型* @since 4.2*/@Nullablepublic Class<? extends Annotation> annotationType() {return this.annotationType;}/**得到类型为String的注解内部属性值。*/public String getString(String attributeName) {return getRequiredAttribute(attributeName, String.class);}/**得到类型为String数组的注解内部属性值。*/public String[] getStringArray(String attributeName) {return getRequiredAttribute(attributeName, String[].class);}/**得到类型为Boolean的注解内部属性值。*/public boolean getBoolean(String attributeName) {return getRequiredAttribute(attributeName, Boolean.class);}/**得到类型为Number的注解内部属性值*/@SuppressWarnings("unchecked")public <N extends Number> N getNumber(String attributeName) {return (N) getRequiredAttribute(attributeName, Number.class);}/**得到类型为Enum的注解内部属性值*/@SuppressWarnings("unchecked")public <E extends Enum<?>> E getEnum(String attributeName) {return (E) getRequiredAttribute(attributeName, Enum.class);}/**得到类型为Class的注解内部属性值比如在ComponentScan注解内部有一个属性为：Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;*/@SuppressWarnings("unchecked")public <T> Class<? extends T> getClass(String attributeName) {return getRequiredAttribute(attributeName, Class.class);}/**得到类型为Class数组的注解内部属性值*/public Class<?>[] getClassArray(String attributeName) {return getRequiredAttribute(attributeName, Class[].class);}/**得到类型为Annotation的注解内部属性值* @since 4.2*/public AnnotationAttributes getAnnotation(String attributeName) {return getRequiredAttribute(attributeName, AnnotationAttributes.class);}/**得到类型为Annotation的注解内部属性值，需指定注解的Class* @since 4.2*/public <A extends Annotation> A getAnnotation(String attributeName, Class<A> annotationType) {return getRequiredAttribute(attributeName, annotationType);}/**得到类型为Annotation数组的注解内部属性值*/public AnnotationAttributes[] getAnnotationArray(String attributeName) {return getRequiredAttribute(attributeName, AnnotationAttributes[].class);}/*** @since 4.2*/@SuppressWarnings("unchecked")public <A extends Annotation> A[] getAnnotationArray(String attributeName, Class<A> annotationType) {Object array = Array.newInstance(annotationType, 0);return (A[]) getRequiredAttribute(attributeName, array.getClass());}/**将Map转化为AnnotationAttributes */@Nullablepublic static AnnotationAttributes fromMap(@Nullable Map<String, Object> map) {if (map == null) {return null;}if (map instanceof AnnotationAttributes) {return (AnnotationAttributes) map;}return new AnnotationAttributes(map);}

核心方法 getRequiredAttribute

private <T> T getRequiredAttribute(String attributeName, Class<T> expectedType) {Assert.hasText(attributeName, "'attributeName' must not be null or empty");Object value = get(attributeName);//调用上一层Map的get的方法assertAttributePresence(attributeName, value);//判断value是否为空assertNotException(attributeName, value);//判断是否抛出异常//getComponentType用于返回表示数组的组件类型的Class//只有数组类型才会有getComponentType，所以这里意思是//如果是数组类型，并且是数组类型正确，就，，，，这个暂时没有理解，如果有知道的，请在下方评论if (!expectedType.isInstance(value) && expectedType.isArray() &&expectedType.getComponentType().isInstance(value)) {Object array = Array.newInstance(expectedType.getComponentType(), 1);Array.set(array, 0, value);value = array;}assertAttributeType(attributeName, value, expectedType);//检查类型是否正确return (T) value;
}private void assertAttributePresence(String attributeName, Object attributeValue) {Assert.notNull(attributeValue, () -> String.format("Attribute '%s' not found in attributes for annotation [%s]",attributeName, this.displayName));
}private void assertNotException(String attributeName, Object attributeValue) {if (attributeValue instanceof Throwable) {throw new IllegalArgumentException(String.format("Attribute '%s' for annotation [%s] was not resolvable due to exception [%s]",attributeName, this.displayName, attributeValue), (Throwable) attributeValue);}
}private void assertAttributeType(String attributeName, Object attributeValue, Class<?> expectedType) {if (!expectedType.isInstance(attributeValue)) {throw new IllegalArgumentException(String.format("Attribute '%s' is of type %s, but %s was expected in attributes for annotation [%s]",attributeName, attributeValue.getClass().getSimpleName(), expectedType.getSimpleName(),this.displayName));}
}

以上那些get方法都是基于getRequiredAttribute实现的。

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AnnotationAttributes

作用

构造函数以及成员

主要方法

核心方法 getRequiredAttribute

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