spring注解工具类AnnotatedElementUtils和AnnotationUtils v一、前言
v一、前言
spring为开发人员提供了两个搜索注解的工具类，分别是AnnotatedElementUtils和AnnotationUtils。在使用的时候，总是傻傻分不清，什么情况下使用哪一个。于是我做了如下的整理和总结。
v二、AnnotationUtils官方解释
v 功能
用于处理注解，处理元注解，桥接方法（编译器为通用声明生成）以及超级方法（用于可选注解继承）的常规实用程序方法。请注意，JDK的内省工具本身并不提供此类的大多数功能。作为运行时保留注解的一般规则（例如，用于事务控制，授权或服务公开），始终在此类上使用查找方法（例如，findAnnotation（Method，Class），getAnnotation（Method，Class）和getAnnotations（方法））而不是JDK中的普通注解查找方法。您仍然可以在给定类级别的get查找（getAnnotation（Method，Class））和给定方法的整个继承层次结构中的查找查找（findAnnotation（Method，Class））之间明确选择。
v 术语
直接呈现，间接呈现和呈现的术语与AnnotatedElement的类级别javadoc中定义的含义相同（在Java 8中）。如果注解被声明为元素上存在的其他注解上的元注解，则注解在元素上是元存在的。如果A在另一个注解上直接存在或元存在，则注解A在另一个注解上存在元。
v 元注解支持
大多数find *（）方法和此类中的一些get *（）方法都支持查找用作元注解的注解。有关详细信息，请参阅此类中每个方法的javadoc。对于在组合注解中使用属性覆盖的元注解的细粒度支持，请考虑使用AnnotatedElementUtils的更具体的方法。
v 属性别名
此类中返回注解，注解数组或AnnotationAttributes的所有公共方法都透明地支持通过@AliasFor配置的属性别名。有关详细信息，请参阅各种synthesizeAnnotation *（..）方法。
v 搜索范围
一旦找到指定类型的第一个注解，此类中的方法使用的搜索算法将停止搜索注解。因此，将默默忽略指定类型的其他注解。
v三、AnnotatedElementUtils官方解释
v 功能
用于在AnnotatedElements上查找注解，元注解和可重复注解的常规实用程序方法。AnnotatedElementUtils为Spring的元注解编程模型定义了公共API，并支持注解属性覆盖。如果您不需要支持注解属性覆盖，请考虑使用AnnotationUtils。请注意，JDK的内省工具本身不提供此类的功能。
v 注解属性覆盖
getMergedAnnotationAttributes（），getMergedAnnotation（），getAllMergedAnnotations（），getMergedRepeatableAnnotations（），findMergedAnnotationAttributes（），findMergedAnnotation（），findAllMergedAnnotations（）和findMergedRepeatableAnnotations（）的所有变体都支持组合注解中带有属性覆盖的元注解的方法。
v 查找与获取语义
获取语义（Get semantics）仅限于搜索AnnotatedElement上存在的注解（即本地声明或继承）或在AnnotatedElement上方的注解层次结构中声明的注解。
查找语义（Find semantics）更加详尽，提供了语义加上对以下内容的支持：
如果带注解的元素是类，则在接口上搜索
如果带注解的元素是类，则在超类上搜索
解析桥接方法，如果带注解的元素是方法
如果带注解的元素是方法，则在接口中搜索方法
如果带注解的元素是方法，则在超类中搜索方法
v 支持@Inherited
get语义之后的方法将遵循Java的@Inherited批注的约定，除了本地声明的注解（包括自定义组合注解）将优于继承注解。相反，查找语义之后的方法将完全忽略@Inherited的存在，因为查找搜索算法手动遍历类型和方法层次结构，从而隐式支持注解继承而不需要@Inherited。
v四、准备两个测试的注解
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@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@interface RequestMapping {
String name() default "";
@AliasFor("path")
String[] value() default {};
@AliasFor("value")
String[] path() default {};
}
@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@RequestMapping
@interface PostMapping {
@AliasFor(annotation = RequestMapping.class)
String name() default "";
@AliasFor(annotation = RequestMapping.class)
String[] value() default {};
@AliasFor(annotation = RequestMapping.class)
String[] path() default {};
}
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v五、测试例子
v 父类拥有注解@RequestMapping，子类没有注解
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public class AnnotationTest {
public static void main(String[] args) {
System.out.println("ParentController getAnnotation @RequestMapping: " + AnnotationUtils.getAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ChildController getAnnotation @RequestMapping: " +AnnotationUtils.getAnnotation(ChildController.class, RequestMapping.class));
System.out.println();
System.out.println("ParentController findAnnotation @RequestMapping: " + AnnotationUtils.findAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ParentController findAnnotation @RequestMapping: " + AnnotationUtils.findAnnotation(ChildController.class, RequestMapping.class));
System.out.println();
System.out.println("ParentController isAnnotated @RequestMapping: " + AnnotatedElementUtils.isAnnotated(ParentController.class, RequestMapping.class));
System.out.println("ParentController getMergedAnnotation @RequestMapping: " + AnnotatedElementUtils.getMergedAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ChildController isAnnotated @RequestMapping: " + AnnotatedElementUtils.isAnnotated(ChildController.class, RequestMapping.class));
System.out.println("ChildController getMergedAnnotation @RequestMapping: " + AnnotatedElementUtils.getMergedAnnotation(ChildController.class, RequestMapping.class));
System.out.println();
System.out.println("ParentController hasAnnotation @RequestMapping: " + AnnotatedElementUtils.hasAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ParentController findMergedAnnotation @RequestMapping: " + AnnotatedElementUtils.findMergedAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ChildController hasAnnotation @RequestMapping: " + AnnotatedElementUtils.hasAnnotation(ChildController.class, RequestMapping.class));
System.out.println("ChildController findMergedAnnotation @RequestMapping: " + AnnotatedElementUtils.findMergedAnnotation(ChildController.class, RequestMapping.class));
}
}
@RequestMapping(value = "parent/controller")
class ParentController {
}
class ChildController extends ParentController {
}
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输出结果如下。
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ParentController getAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ChildController getAnnotation @RequestMapping: null
ParentController findAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ChildController findAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ParentController isAnnotated @RequestMapping: true
ParentController getMergedAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ChildController isAnnotated @RequestMapping: false
ChildController getMergedAnnotation @RequestMapping: null
ParentController hasAnnotation @RequestMapping: true
ParentController findMergedAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ChildController hasAnnotation @RequestMapping: true
ChildController findMergedAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
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v 父类没有注解，子类拥有注解@RequestMapping
输出结果如下。
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ParentController getAnnotation @RequestMapping: null
ChildController getAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ParentController findAnnotation @RequestMapping: null
ChildController findAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ParentController isAnnotated @RequestMapping: false
ParentController getMergedAnnotation @RequestMapping: null
ChildController isAnnotated @RequestMapping: true
ChildController getMergedAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ParentController hasAnnotation @RequestMapping: false
ParentController findMergedAnnotation @RequestMapping: null
ChildController hasAnnotation @RequestMapping: true
ChildController findMergedAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
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v 父类拥有注解@PostMapping，子类没有注解
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public class AnnotationTest {
public static void main(String[] args) {
System.out.println("ParentController getAnnotation @RequestMapping: " + AnnotationUtils.getAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ChildController getAnnotation @RequestMapping: " +AnnotationUtils.getAnnotation(ChildController.class, RequestMapping.class));
System.out.println("ParentController getAnnotation @PostMapping: " + AnnotationUtils.getAnnotation(ParentController.class, PostMapping.class));
System.out.println("ChildController getAnnotation @PostMapping: " +AnnotationUtils.getAnnotation(ChildController.class, PostMapping.class));
System.out.println();
System.out.println("ParentController findAnnotation @RequestMapping: " + AnnotationUtils.findAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ParentController findAnnotation @RequestMapping: " + AnnotationUtils.findAnnotation(ChildController.class, RequestMapping.class));
System.out.println("ParentController findAnnotation @PostMapping: " + AnnotationUtils.findAnnotation(ParentController.class, PostMapping.class));
System.out.println("ParentController findAnnotation @PostMapping: " + AnnotationUtils.findAnnotation(ChildController.class, PostMapping.class));
System.out.println();
System.out.println("ParentController isAnnotated @RequestMapping: " + AnnotatedElementUtils.isAnnotated(ParentController.class, RequestMapping.class));
System.out.println("ParentController getMergedAnnotation @RequestMapping: " + AnnotatedElementUtils.getMergedAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ParentController isAnnotated @PostMapping: " + AnnotatedElementUtils.isAnnotated(ParentController.class, PostMapping.class));
System.out.println("ParentController getMergedAnnotation @PostMapping: " + AnnotatedElementUtils.getMergedAnnotation(ParentController.class, PostMapping.class));
System.out.println("ChildController isAnnotated @RequestMapping: " + AnnotatedElementUtils.isAnnotated(ChildController.class, RequestMapping.class));
System.out.println("ChildController getMergedAnnotation @RequestMapping: " + AnnotatedElementUtils.getMergedAnnotation(ChildController.class, RequestMapping.class));
System.out.println("ChildController isAnnotated @PostMapping: " + AnnotatedElementUtils.isAnnotated(ChildController.class, PostMapping.class));
System.out.println("ChildController getMergedAnnotation @PostMapping: " + AnnotatedElementUtils.getMergedAnnotation(ChildController.class, PostMapping.class));
System.out.println();
System.out.println("ParentController hasAnnotation @RequestMapping: " + AnnotatedElementUtils.hasAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ParentController findMergedAnnotation @RequestMapping: " + AnnotatedElementUtils.findMergedAnnotation(ParentController.class, RequestMapping.class));
System.out.println("ParentController hasAnnotation @PostMapping: " + AnnotatedElementUtils.hasAnnotation(ParentController.class, PostMapping.class));
System.out.println("ParentController findMergedAnnotation @PostMapping: " + AnnotatedElementUtils.findMergedAnnotation(ParentController.class, PostMapping.class));
System.out.println("ChildController hasAnnotation @RequestMapping: " + AnnotatedElementUtils.hasAnnotation(ChildController.class, RequestMapping.class));
System.out.println("ChildController findMergedAnnotation @RequestMapping: " + AnnotatedElementUtils.findMergedAnnotation(ChildController.class, RequestMapping.class));
System.out.println("ChildController hasAnnotation @PostMapping: " + AnnotatedElementUtils.hasAnnotation(ChildController.class, PostMapping.class));
System.out.println("ChildController findMergedAnnotation @PostMapping: " + AnnotatedElementUtils.findMergedAnnotation(ChildController.class, PostMapping.class));
}
}
@PostMapping(value = "parent/controller")
class ParentController {
}
class ChildController extends ParentController {
}
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输出结果如下。
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ParentController getAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[], path=[])
ChildController getAnnotation @RequestMapping: null
ParentController getAnnotation @PostMapping: @com.hjzgg.apigateway.test.service.main.PostMapping(name=, value=[parent/controller], path=[parent/controller])
ChildController getAnnotation @PostMapping: null
ParentController findAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[], path=[])
ChildController findAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[], path=[])
ParentController findAnnotation @PostMapping: @com.hjzgg.apigateway.test.service.main.PostMapping(name=, value=[parent/controller], path=[parent/controller])
ChildController findAnnotation @PostMapping: @com.hjzgg.apigateway.test.service.main.PostMapping(name=, value=[parent/controller], path=[parent/controller])
ParentController isAnnotated @RequestMapping: true
ParentController getMergedAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ParentController isAnnotated @PostMapping: true
ParentController getMergedAnnotation @PostMapping: @com.hjzgg.apigateway.test.service.main.PostMapping(name=, value=[parent/controller], path=[parent/controller])
ChildController isAnnotated @RequestMapping: false
ChildController getMergedAnnotation @RequestMapping: null
ChildController isAnnotated @PostMapping: false
ChildController getMergedAnnotation @PostMapping: null
ParentController hasAnnotation @RequestMapping: true
ParentController findMergedAnnotation @RequestMapping: @com.hjzgg.apigateway.test.service.main.RequestMapping(name=, value=[parent/controller], path=[parent/controller])
ParentController hasAnnotation @PostMapping: true
ParentController findMergedAnnotation @PostMapping: @com.hjzgg.apigateway.test.service.main.PostMapping(name=, value=[parent/controller], path=[parent/controller])
ChildController hasAnnotation @RequestMapping: true
ChildController findM
