@Target({ ElementType.FIELD}) 
//只允許用在類的字段上
@Retention(RetentionPolicy.RUNTIME) 
//注解保留在程序運行期間，此時可以通過反射獲得定義在某個類上的所有注解
@Constraint(validatedBy = ParamConstraintValidated.class)
public @interface Check {
  /**
   * 合法的參數(shù)值
   **/
  String[] paramValues();
 
  /**
   * 提示信息
   **/
  String message() default "參數(shù)不為指定值";
 
  Class<?>[] groups() default {};
 
  Class<? extends Payload>[] payload() default {};
}

public class ParamConstraintValidated implements ConstraintValidator<Check, Object> {
  /**
   * 合法的參數(shù)值，從注解中獲取
   * */
  private List<String> paramValues;
 
  @Override
  public void initialize(Check constraintAnnotation) {
    //初始化時獲取注解上的值
    paramValues = Arrays.asList(constraintAnnotation.paramValues());
  }
 
  public boolean isValid(Object o, ConstraintValidatorContext constraintValidatorContext) {
    if (paramValues.contains(o)) {
      return true;
    }
 
    //不在指定的參數(shù)列表中
    return false;
  }
}

@Data
public class User {
  /**
   * 姓名
   * */
  private String name;
 
  /**
   * 性別 man or women
   * */
  @Check(paramValues = {"man", "woman"})
  private String sex;
}

@RestController("/api/test")
public class TestController {
  @PostMapping
  public Object test(@Validated @RequestBody User user) {
    return "hello world";
  }
}

@Target({ ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface PermissionCheck {
  /**
   * 資源key
   * */
  String resourceKey();
}

public class PermissionCheckInterceptor extends HandlerInterceptorAdapter {
  /**
   * 處理器處理之前調用
   */
  @Override
  public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
               Object handler) throws Exception {
    HandlerMethod handlerMethod = (HandlerMethod)handler;
    PermissionCheck permission = findPermissionCheck(handlerMethod);
 
    //如果沒有添加權限注解則直接跳過允許訪問
    if (permission == null) {
      return true;
    }
 
    //獲取注解中的值
    String resourceKey = permission.resourceKey();
 
    //TODO 權限校驗一般需要獲取用戶信息，通過查詢數(shù)據(jù)庫進行權限校驗
    //TODO 這里只進行簡單演示，如果resourceKey為testKey則校驗通過，否則不通過
    if ("testKey".equals(resourceKey)) {
      return true;
    }
 
    return false;
  }
 
  /**
   * 根據(jù)handlerMethod返回注解信息
   *
   * @param handlerMethod 方法對象
   * @return PermissionCheck注解
   */
  private PermissionCheck findPermissionCheck(HandlerMethod handlerMethod) {
    //在方法上尋找注解
    PermissionCheck permission = handlerMethod.getMethodAnnotation(PermissionCheck.class);
    if (permission == null) {
      //在類上尋找注解
      permission = handlerMethod.getBeanType().getAnnotation(PermissionCheck.class);
    }
 
    return permission;
  }
}

 @GetMapping("/api/test")
 @PermissionCheck(resourceKey = "test")
 public Object testPermissionCheck() {
   return "hello world";
 }

@Target({ ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface CustomCache {
  /**
   * 緩存的key值
   * */
  String key();
}

@Aspect
@Component
public class CustomCacheAspect {
  /**
   * 在方法執(zhí)行之前對注解進行處理
   *
   * @param pjd
   * @param customCache 注解
   * @return 返回中的值
   * */
  @Around("@annotation(com.cqupt.annotation.CustomCache) && @annotation(customCache)")
  public Object dealProcess(ProceedingJoinPoint pjd, CustomCache customCache) {
    Object result = null;
 
    if (customCache.key() == null) {
      //TODO throw error
    }
 
    //TODO 業(yè)務場景會比這個復雜的多，會涉及參數(shù)的解析如key可能是#{id}這些，數(shù)據(jù)查詢
    //TODO 這里做簡單演示，如果key為testKey則返回hello world
    if ("testKey".equals(customCache.key())) {
      return "hello word";
    }
 
    //執(zhí)行目標方法
    try {
      result = pjd.proceed();
    } catch (Throwable throwable) {
      throwable.printStackTrace();
    }
 
    return result;
  }
}

@GetMapping("/api/cache")
@CustomCache(key = "test")
public Object testCustomCache() {
  return "don't hit cache";
}