從一個類上獲取不到註解的原因
阿新 • • 發佈:2022-03-25
場景
定義一個註解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotation {
}
一個父類
@MyAnnotation
public class OneClass {
}
一個子類
public class TwoClass extends OneClass {
}
public class Main { public static void main(String[] args) { System.out.println(OneClass.class.getAnnotation(MyAnnotation.class)); System.out.println(TwoClass.class.getAnnotation(MyAnnotation.class)); } }
@cn.eagle.li.java.reflect.annnotation.MyAnnotation()
null
可以看出 從子類身上是獲取不到 註解的
解決方案:
- 使用
Spring中的工具類 AnnotationUtils
public class Main { public static void main(String[] args) { System.out.println(OneClass.class.getAnnotation(MyAnnotation.class)); System.out.println(TwoClass.class.getAnnotation(MyAnnotation.class)); System.out.println(AnnotationUtils.findAnnotation(TwoClass.class, MyAnnotation.class)); } }
@cn.eagle.li.java.reflect.annnotation.MyAnnotation()
null
@cn.eagle.li.java.reflect.annnotation.MyAnnotation()
- 在註解上加上元註解
@Inherited
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
public @interface MyAnnotation {
}
public class Main { public static void main(String[] args) { System.out.println(OneClass.class.getAnnotation(MyAnnotation.class)); System.out.println(TwoClass.class.getAnnotation(MyAnnotation.class)); System.out.println(AnnotationUtils.findAnnotation(TwoClass.class, MyAnnotation.class)); } }
@cn.eagle.li.java.reflect.annnotation.MyAnnotation()
@cn.eagle.li.java.reflect.annnotation.MyAnnotation()
@cn.eagle.li.java.reflect.annnotation.MyAnnotation()