SpringMVC中HandlerInterceptor诡异问题排查的示例分析
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发现问题
最近在进行压测发现,有一些接口时好时坏,通过sentry日志平台及sky walking平台跟踪发现,用户张三获取到的用户上下文确是李四。
代码走读
用户登录下上文
/** * 用户登录下上文 * * @author : jamesfu * @date : 22/5/2019 * @time : 9:18 AM */ @Data public class UserContext { private final static ThreadLocalthreadLocal = new ThreadLocal<>(); private Long id; private String loginName; public static UserContext get() { UserContext context = threadLocal.get(); if (context == null) { // TODO(james.h.fu):根据请求上下文获取token, 然后恢复用户登录下上文 context = new UserContext() {{ setId(1L); setLoginName("james.h.fu1"); }}; threadLocal.set(context); } return context; } public static void clear() { threadLocal.remove(); } public static void set(UserContext context) { if (context != null) { threadLocal.set(context); } } }
在拦截器中有调用UserContext.set恢复用户登录上下文,并在请求结束时调用UserContext.clear清理用户登录上下文。
拦截器注册配置
/** * 拦截器注册配置 * * @author : jamesfu * @date : 22/5/2019 * @time : 9:15 AM */ @Configuration public class FilterConfig implements WebMvcConfigurer { @Autowired private JsonRpcInterceptor jsonRpcInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(jsonRpcInterceptor) .addPathPatterns("/json.rpc"); } }
通过debug可以发现UserContext中的ThreadLocal的清理工作没有得到执行。导致请求进来时,有可能ThreadLocal已存在了,就不会再根据请求上下文恢复了。
springmvc 源码走读
tomcat 在收到http请求后,最终会交由spring mvc的 DispatcherServlet
处理。 这里可以从doDispatch按图索骥,顺藤摸瓜地往下看起走。
源码走读:DispatcherServlet
/** * Process the actual dispatching to the handler. *The handler will be obtained by applying the servlet's HandlerMappings in order. * The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters * to find the first that supports the handler class. *
All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers * themselves to decide which methods are acceptable. * @param request current HTTP request * @param response current HTTP response * @throws Exception in case of any kind of processing failure */ protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception
请求会得到分发,然后执行各个已注册Handler的preHandle-->postHandle-->afterCompletion。
源码走读:HandlerExecutionChain applyPreHandle
/** * Apply preHandle methods of registered interceptors. * @return {@code true} if the execution chain should proceed with the * next interceptor or the handler itself. Else, DispatcherServlet assumes * that this interceptor has already dealt with the response itself. */ boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception { HandlerInterceptor[] interceptors = getInterceptors(); if (!ObjectUtils.isEmpty(interceptors)) { for (int i = 0; i < interceptors.length; i++) { HandlerInterceptor interceptor = interceptors[i]; if (!interceptor.preHandle(request, response, this.handler)) { triggerAfterCompletion(request, response, null); return false; } this.interceptorIndex = i; } } return true; }
当执行到preHandle返回false时,它就会从上一个返回true的handler依次往前执行afterCompletion,它自己的afterCompletion得不到执行。
triggerAfterCompletion
/** * Trigger afterCompletion callbacks on the mapped HandlerInterceptors. * Will just invoke afterCompletion for all interceptors whose preHandle invocation * has successfully completed and returned true. */ void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) throws Exception { HandlerInterceptor[] interceptors = getInterceptors(); if (!ObjectUtils.isEmpty(interceptors)) { for (int i = this.interceptorIndex; i >= 0; i--) { HandlerInterceptor interceptor = interceptors[i]; try { interceptor.afterCompletion(request, response, this.handler, ex); } catch (Throwable ex2) { logger.error("HandlerInterceptor.afterCompletion threw exception", ex2); } } } }
triggerAfterCompletion只会在(1)出现异常,(2)preHandle返回false 或(3)正常执行结束才会从索引interceptorIndex依次往前执行。
所以基于以上源码可以得知,在写拦截器时preHandle返回false时,afterCompletion是不会执行的。所以一些必要的清理工作得不到执行,会出现类似我们遇到的帐号串的问题。
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