Spring 自定义注解玩法大全，从入门到…

@Target({ ElementType.FIELD}) //只允许用在类的字段上
@Retention(RetentionPolicy.RUNTIME) //注解保留在程序运行期间，此时可以通过反射获得定义在某个类上的所有注解
@Constraint(validatedBy = ParamConstraintValidated.class)
public @interface Check {
    /**
     * 合法的参数值
     * */
    String[] paramValues();
    /**
     * 提示信息
     * */
    String message() default "参数不为指定值";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

public class ParamConstraintValidated implements ConstraintValidator<Check, Object> {
    /**
     * 合法的参数值，从注解中获取
     * */
    private List<String> paramValues;
    @Override
    public void initialize(Check constraintAnnotation) {
        //初始化时获取注解上的值
        paramValues = Arrays.asList(constraintAnnotation.paramValues());
    }
    public boolean isValid(Object o, ConstraintValidatorContext constraintValidatorContext) {
        if (paramValues.contains(o)) {
            return true;
        }
}

@Data
public class User {
    /**
     * 姓名
     * */
    private String name;
    /**
     * 性别 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 {
    /**
     * 资源key
     * */
    String resourceKey();
}

public class PermissionCheckInterceptor extends HandlerInterceptorAdapter {
    /**
     * 处理器处理之前调用
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response,
                             Object handler) throws Exception {
        HandlerMethod handlerMethod = (HandlerMethod)handler;
        PermissionCheck permission = findPermissionCheck(handlerMethod);
        //如果没有添加权限注解则直接跳过允许访问
        if (permission == null) {
            return true;
        }
        //获取注解中的值
        String resourceKey = permission.resourceKey();
        //TODO 权限校验一般需要获取用户信息，通过查询数据库进行权限校验
        //TODO 这里只进行简单演示，如果resourceKey为testKey则校验通过，否则不通过
        if ("testKey".equals(resourceKey)) {
            return true;
        }
        return false;
    }
    /**
     * 根据handlerMethod返回注解信息
     *
     * @param handlerMethod 方法对象
     * @return PermissionCheck注解
     */
    private PermissionCheck findPermissionCheck(HandlerMethod handlerMethod) {
        //在方法上寻找注解
        PermissionCheck permission = handlerMethod.getMethodAnnotation(PermissionCheck.class);
        if (permission == null) {
            //在类上寻找注解
            permission = handlerMethod.getBeanType().getAnnotation(PermissionCheck.class);
        }
        return permission;
    }
}

@Aspect
@Component
public class CustomCacheAspect {
    /**
     * 在方法执行之前对注解进行处理
     *
     * @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 业务场景会比这个复杂的多，会涉及参数的解析如key可能是#{id}这些，数据查询
        //TODO 这里做简单演示，如果key为testKey则返回hello world
        if ("testKey".equals(customCache.key())) {
            return "hello word";
        }
        //执行目标方法
        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";
}