这篇文章给大家分享的是有关SpringMVC中HandlerInterceptor诡异问题排查的示例分析的内容。小编觉得挺实用的，因此分享给大家做个参考，一起跟随小编过来看看吧。
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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 ThreadLocal threadLocal = 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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