code: public static <A extends Annotation> A getAnnotation(Field field, Class<A> annotationType) {
          if (field == null || annotationType == null) {
              return null;
          }
  
          return field.getAnnotation(annotationType);
      }
docs: 获取<code>Field</code>上的注解
  
  @param field          属性
  @param annotationType 注解类型
  
  @return 注解对象