Annotation 注解修饰

@Rentention (注解的保留时间，SOURCE（源码）、CLASS（编译）、RUNTIME（运行时）)默认为CLASS
@Documented：是否会保存到javadoc文档中
@Target：用来修饰哪些程序的元素，如 TYPE，METHOD，CONSTRUCTOR、FILED、PARAMETER

自定义一个注解类 @UserGroup

@Retention(RetentionPolicy.RUNTIME)
@Target({ELementType.FIELD,ElementType.METHOD})
public @interface UserGroup{
       int age();
}

然后接下来就是调用

@Slf4j
public class TestAnnotation {
  @UserGroup(age = 20)
  private int age;
        
  public int setAge(int age){
        this.age = age;
        log.info("\n" + "age : " + this.age);
        return this.age;
    }

public static void  main(String[] args)throws InstantiationException, IllegalAccessException,InvocationTargetException,NoSuchMethodException{
        TestAnnotation testAnnotation = new TestAnnotation();
        testAnnotation.setage();
    } 

public void  setage() throws InstantiationException, IllegalAccessException,NoSuchMethodException, InvocationTargetException {
        Class class1 = TestAnnotation.class;
        for (Field field:class1.getDeclaredFields()){
            if(field.isAnnotationPresent(UserGroup.class)){
                UserGroup annotation = field.getAnnotation(UserGroup.class);
                int age1 = annotation.age();
                Method method = class1.getDeclaredMethod("setAge", int.class);
                method.invoke(class1.newInstance(),age1);
            }
        }
    }