5分钟搞懂java注解@Annotation的具体使用

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface Service {

 String value() default "";
 
}

public enum ElementType {
  /** Class, interface (including annotation type), or enum declaration */
  TYPE,

  /** Field declaration (includes enum constants) */
  FIELD,

  /** Method declaration */
  METHOD,

  /** Formal parameter declaration */
  PARAMETER,

  /** Constructor declaration */
  CONSTRUCTOR,

  /** Local variable declaration */
  LOCAL_VARIABLE,

  /** Annotation type declaration */
  ANNOTATION_TYPE,

  /** Package declaration */
  PACKAGE,

  /**
   * Type parameter declaration
   *
   * @since 1.8
   */
  TYPE_PARAMETER,

  /**
   * Use of a type
   *
   * @since 1.8
   */
  TYPE_USE
}

public enum RetentionPolicy {
  /**
   * Annotations are to be discarded by the compiler.
   */
  SOURCE,

  /**
   * Annotations are to be recorded in the class file by the compiler
   * but need not be retained by the VM at run time. This is the default
   * behavior.
   */
  CLASS,

  /**
   * Annotations are to be recorded in the class file by the compiler and
   * retained by the VM at run time, so they may be read reflectively.
   *
   * @see java.lang.reflect.AnnotatedElement
   */
  RUNTIME
}

@Inherited
public @interface A{
}

@A
public class Parent{}

public class Son entends Parant{}//Son类继承了父类的A注解

@Repeatable(Schedules.class)
public @interface Schedule {
  String date();
}

public @interface Schedules {
  Schedule[] value();
}

@Schedule(date = "周一")
@Schedule(date = "周三")
public class Executor {
}

public enum IdentityEnums {

  SUPER_ADMIN,
  ADMIN,
  VISIVOR

}

@Target({ElementType.TYPE,ElementType.METHOD})
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface Authorization {

  IdentityEnums[] value();
  
}

public class AuthInterceptor implements HandlerInterceptor {

  @Override
  public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

    if (handler instanceof HandlerMethod)
    {
      IdentityEnums user = getIdentityFromRequset(request);//这里从request里获取账号信息并判断身份，自己实现
      Authorization auth =((HandlerMethod) handler).getMethodAnnotation(Authorization.class);//获取方法上面的注解
      if (!Arrays.asList(auth.value()).contains(user)){
        return false;
      }
    }
    return true;
  }
}

<!-- 拦截器 -->
 <mvc:interceptors>
 <mvc:interceptor>
  <!-- 匹配的是url路径， 如果不配置或/**,将拦截所有的Controller -->
  <mvc:mapping path="/**" />
  <!-- 拦截器类 -->
  <bean
  class="com.xx.xx.AuthInterceptor"></bean>
 </mvc:interceptor>
 </mvc:interceptors>

@RequestMapping(value = "/management")
@Authorization({IdentityEnums.ADMIN,IdentityEnums.SUPER_ADMIN})
public String management(HttpServletRequest request, HttpServletResponse response)
{
  log.info("has permission!");
}