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浅谈SpringMVC HandlerInterceptor诡异问题排查

2019年07月19日  | 移动技术网IT编程  | 我要评论

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<usercontext> 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.
	 * <p>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.
	 * <p>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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