### 背景
>最近项目有个需求，需要对第三方接口调用加入调用次数限制。随设计自定义注解，使用拦截器拦截方法请求，将单位时间内的请求次数保存到redis。超出限制次数的请求直接拒绝或者异常处理。
### 1.自定义注解
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD,ElementType.TYPE,ElementType.METHOD})
@Documented
public @interface AccessLimit {
/**
* 单位时间内允许访问的次数，默认60
* @return
*/
int maxCount() default 60;
/**
* 单位时间为1分钟,即默认限流为一分钟最大调用60次
* @return
*/
long time() default 1;
}
### 2.添加拦截器
```java
@Configuration
@Slf4j
public class AccessLimitInterceptor implements HandlerInterceptor {
@Autowired
private RedisUtil redisUtil;
@Autowired
private MessageSource messageSource;
@Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
//请求输入方法
if(handler instanceof HandlerMethod){
HandlerMethod handlerMethod = (HandlerMethod) handler;
Method method = handlerMethod.getMethod();
if (!method.isAnnotationPresent(AccessLimit.class)) {
return true;
}
AccessLimit accessLimit = method.getAnnotation(AccessLimit.class);
if (accessLimit == null) {
return true;
}
int maxCount = accessLimit.maxCount();
long time = accessLimit.time();
//存入redis中的key值
String key = IpUtils.getIpAddr(request) + Constants.COLON + request.getRequestURI();
try {
//第一次访问将次数+1
long visitTimes = redisUtil.increment(key,1);
//第一次访问时设置过期时间
if(1 == visitTimes){
redisUtil.setExpire(key,visitTimes,time, TimeUnit.MINUTES);
}
if(visitTimes > maxCount){
frequentRequest(response,messageSource);
return false;
}
}catch (Exception e){
log.error("方法拦截中redis操作异常：" + e);
return false;
}
}
return true;
}
@Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
ModelAndView modelAndView) throws Exception {
// TODO Auto-generated method stub
HandlerInterceptor.super.postHandle(request, response, handler, modelAndView);
}
@Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
throws Exception {
// TODO Auto-generated method stub
HandlerInterceptor.super.afterCompletion(request, response, handler, ex);
}
/**
* 接口请求频繁异常处理
* @param response 请求响应
* @param messageSource
*/
private void frequentRequest(HttpServletResponse response,MessageSource messageSource){
try {
BaseResponse baseResponse = new BaseResponse();
baseResponse.setState(ResultCode.FREQUENT_REQUEST_CODE.getValue());
baseResponse.setStateDesc(InterUtils.interInfo(InterUtils.defLanguage, messageSource, "request.too.frequent"));
response.setCharacterEncoding("utf-8");
response.setContentType("application/json; charset=utf-8");
PrintWriter writer = response.getWriter();
JSONObject json = (JSONObject) JSONObject.toJSON(baseResponse);
writer.write(json.toString());
}catch (IOException e){
log.error("IO异常:" + e.getMessage(), e);
}
}
}
```
### 3. 配置拦截器bean
@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
@Bean
public AccessLimitInterceptor getAccessLimitInterceptor(){
return new AccessLimitInterceptor();
}
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(getAccessLimitInterceptor()).addPathPatterns("/**");//.excludePathPatterns("/login");
}
}
### 4.接口方法使用注解
@PostMapping("/api/sdk")
@AccessLimit(maxCount = 100,time = 60)
public String sdk(HttpServletRequest request){
...
}
### 5.总结
从代码层面来考虑的话，此方式实现还是比较优雅的，对业务层也没有太多的耦合。且此种方式单体和分布式均适用，因为用户实际的访问次数都是存在redis容器里的，和应用的单体或分布式无关。
API简单限流实现
