这是坚持技术写作计划（含翻译）的第8篇，定个小目标999，每周最少2篇。
前段时间的文章多是运维方面的，最近放出一波后端相关的。
背景
最近开始使用Sentinel进行流量保护，但是默认的web servlet filter是拦截全部http请求。在传统的项目中问题不大。但是如果项目中用了Spring MVC，并且用了@PathVariable就尴尬了。
比如 uri pattern是/foo/{id} ,而从Sentinel监控看 /foo/1 和 /foo/2 就是两个资源了，并且Sentinel最大支持6000个资源，再多就不生效了。 解决办法
官方给的方案是:UrlCleaner
WebCallbackManager.setUrlCleaner(new UrlCleaner() { @Override public String clean(String originUrl) { if (originUrl.startsWith(fooPrefix)) { return "/foo/*"; } return originUrl; } });复制代码 但是想想就吐， /v1/{foo}/{bar}/qux/{baz} 这种的来个20来个，截一个我看看。
AOP
换种思路，uri pattern难搞，用笨办法 aop总行吧？答案是可以的。
@Aspectpublic class SentinelResourceAspect { @Pointcut("within(com.anjia.*.web.rest..*)") public void sentinelResourcePackagePointcut() { // Method is empty as this is just a Pointcut, the implementations are // in the advices. } @Around("sentinelResourcePackagePointcut()") public Object sentinelResourceAround(ProceedingJoinPoint joinPoint) throws Throwable { Entry entry = null; // 务必保证finally会被执行 try { // 资源名可使用任意有业务语义的字符串 // 注意此处只是类名#方法名，方法重载是合并的，如果需要进行区分， // 可以获取参数类型加入到资源名称上 entry = SphU.entry(joinPoint.getSignature().getDeclaringTypeName()+ "#"+joinPoint.getSignature().getName()); // 被保护的业务逻辑 // do something... } catch (BlockException ex) { // 资源访问阻止，被限流或被降级 // 进行相应的处理操作 } finally { if (entry != null) { entry.exit(); } } return result; }}复制代码 拦截器
温习一下 Spring mvc的执行流程 doFilter -> doService -> dispatcher -> preHandle -> controller -> postHandle -> afterCompletion -> filterAfter
核心的是 String pattern = (String) request.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE); 但是是在dispatcher阶段才赋值的，所以在CommFilter是取不到的，所以导致使用官方的Filter是不行的。只能用拦截器
import com.alibaba.csp.sentinel.EntryType;import com.alibaba.csp.sentinel.SphU;import com.alibaba.csp.sentinel.adapter.servlet.callback.RequestOriginParser;import com.alibaba.csp.sentinel.adapter.servlet.callback.UrlCleaner;import com.alibaba.csp.sentinel.adapter.servlet.callback.WebCallbackManager;import com.alibaba.csp.sentinel.adapter.servlet.util.FilterUtil;import com.alibaba.csp.sentinel.context.ContextUtil;import com.alibaba.csp.sentinel.log.RecordLog;import com.alibaba.csp.sentinel.slots.block.BlockException;import com.alibaba.csp.sentinel.util.StringUtil;import org.apache.commons.lang3.StringUtils;import org.springframework.web.servlet.HandlerInterceptor;import org.springframework.web.servlet.HandlerMapping;import org.springframework.web.servlet.ModelAndView;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;@Componentpublic class SentinelHandlerInterceptor implements HandlerInterceptor { @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { String origin = parseOrigin(request); String pattern = (String) request.getAttribute(HandlerMapping.BEST_MATCHING_PATTERN_ATTRIBUTE); String uriTarget = StringUtils.defaultString(pattern,FilterUtil.filterTarget(request)); try { // Clean and unify the URL. // For REST APIs, you have to clean the URL (e.g. `/foo/1` and `/foo/2` -> `/foo/:id`), or // the amount of context and resources will exceed the threshold. UrlCleaner urlCleaner = WebCallbackManager.getUrlCleaner(); if (urlCleaner != null) { uriTarget = urlCleaner.clean(uriTarget); } RecordLog.info(String.format("[Sentinel Pre Filter] Origin: %s enter Uri Path: %s", origin, uriTarget)); SphU.entry(uriTarget, EntryType.IN); return true; } catch (BlockException ex) { RecordLog.warn(String.format("[Sentinel Pre Filter] Block Exception when Origin: %s enter fall back uri: %s", origin, uriTarget), ex); WebCallbackManager.getUrlBlockHandler().blocked(request, response, ex); return false; } } @Override public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception { while (ContextUtil.getContext() != null && ContextUtil.getContext().getCurEntry() != null) { ContextUtil.getContext().getCurEntry().exit(); } ContextUtil.exit(); } @Override public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception { } private String parseOrigin(HttpServletRequest request) { RequestOriginParser originParser = WebCallbackManager.getRequestOriginParser(); String origin = EMPTY_ORIGIN; if (originParser != null) { origin = originParser.parseOrigin(request); if (StringUtil.isEmpty(origin)) { return EMPTY_ORIGIN; } } return origin; } private static final String EMPTY_ORIGIN = "";}复制代码 import org.springframework.context.annotation.Configuration;import org.springframework.web.servlet.config.annotation.InterceptorRegistry;import org.springframework.web.servlet.config.annotation.WebMvcConfigurationSupport;@Configurationpublic class WebConfig extends WebMvcConfigurerAdapter { @Inject SentinelHandlerInterceptor sentinelHandlerInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(sentinelHandlerInterceptor); }}复制代码 UrlBlockHandler和UrlCleaner和WebServletConfig.setBlockPage(blockPage)
上面说过，UrlCleaner是为了归并请求，清洗url用的。而UrlBlockHandler是在被拦截后的默认处理器。但是clean和handler都不是链式的，所以如果有多种处理，需要自己在一个方法里，进行逻辑判断。
UrlCleaner
WebCallbackManager.setUrlCleaner(new UrlCleaner() { @Override public String clean(String originUrl) { if (originUrl.startsWith(fooPrefix)) { return "/foo/*"; } return originUrl; } });复制代码 UrlBlockHandler
如果通用一点的，可以自己根据request的 content-type进行自适应返回内容(PLAN_TEXT和JSON)WebCallbackManager.setUrlBlockHandler((request, response, ex) -> { response.addHeader("Content-Type","application/json;charset=UTF-8"); PrintWriter out = response.getWriter(); out.print("{\"code\"":429,\"msg\":\"系统繁忙，请稍后重试\""}"); out.flush(); out.close();});复制代码 WebServletConfig.setBlockPage(blockPage)
WebServletConfig.setBlockPage("http://www.baidu.com")复制代码 注意，三个方法都不是不支持调用链，比如我写两个UrlBlockHandler,只认最后一个。
参考资料
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