Arthas实践：是哪个Controller处理了请求？

分手后的思念是犯贱 2022-10-02 02:48 101阅读 0赞

[2019独角兽企业重金招聘Python工程师标准>>> ][2019_Python_] ![hot3.png][]

## 背景 ##

Arthas是阿里巴巴开源的Java诊断利器，深受开发者喜爱。

*  [https://github.com/alibaba/arthas][https_github.com_alibaba_arthas]
 *  [Arthas在线教程][Arthas]

之前分享了Arthas怎样排查 404/401 的问题: [http://hengyunabc.github.io/arthas-spring-boot-404-401/][http_hengyunabc.github.io_arthas-spring-boot-404-401]

我们可以快速定位一个请求是被哪些`Filter`拦截的，或者请求最终是由哪些`Servlet`处理的。

但有时，我们想知道一个请求是被哪个Spring MVC Controller处理的。如果翻代码的话，会比较难找，并且不一定准确。

通过Arthas可以精确定位是哪个`Controller`处理请求。

## Demo ##

还是以这个demo为例： [https://github.com/hengyunabc/spring-boot-inside/tree/master/demo-404-401][https_github.com_hengyunabc_spring-boot-inside_tree_master_demo-404-401]

启动之后，访问： [http://localhost:8080/user/1][http_localhost_8080_user_1] ，会返回一个user对象。那么这个请求是被哪个`Controller`处理的呢？

## trace定位DispatcherServlet ##

我们先试下跟踪`Servlet`：

trace javax.servlet.Servlet *

从trace的结果可以看出来，请求最终是被`DispatcherServlet#doDispatch()`处理了，但是没有办法知道是哪个`Controller`处理。

`---[27.453122ms] org.springframework.web.servlet.DispatcherServlet:doDispatch()
        +---[0.005822ms] org.springframework.web.context.request.async.WebAsyncUtils:getAsyncManager() #929
        +---[0.107365ms] org.springframework.web.servlet.DispatcherServlet:checkMultipart() #936
        |   `---[0.062451ms] org.springframework.web.servlet.DispatcherServlet:checkMultipart()
        |       `---[0.016924ms] org.springframework.web.multipart.MultipartResolver:isMultipart() #1093
        +---[2.103935ms] org.springframework.web.servlet.DispatcherServlet:getHandler() #940
        |   `---[2.036042ms] org.springframework.web.servlet.DispatcherServlet:getHandler()

## watch定位handler ##

trace结果里把调用的行号打印出来了，我们可以直接在IDE里查看代码（也可以用jad命令反编译）：

// org.springframework.web.servlet.DispatcherServlet
    	protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
    		HttpServletRequest processedRequest = request;
    		HandlerExecutionChain mappedHandler = null;
    		boolean multipartRequestParsed = false;
    
    		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
    
    		try {
    			ModelAndView mv = null;
    			Exception dispatchException = null;
    
    			try {
    				processedRequest = checkMultipart(request);
    				multipartRequestParsed = (processedRequest != request);
    
    				// Determine handler for the current request.
    				mappedHandler = getHandler(processedRequest);
    				if (mappedHandler == null || mappedHandler.getHandler() == null) {
    					noHandlerFound(processedRequest, response);
    					return;
    				}

*  仔细看代码，可以发现`mappedHandler = getHandler(processedRequest);`得到了处理请求的handler

下面用`watch`命令来获取`getHandler`函数的返回结果。

`watch`之后，再次访问 [http://localhost:8080/user/1][http_localhost_8080_user_1]

$ watch org.springframework.web.servlet.DispatcherServlet getHandler returnObj
    Press Q or Ctrl+C to abort.
    Affect(class-cnt:1 , method-cnt:1) cost in 332 ms.
    ts=2019-06-04 11:38:06; [cost=2.75218ms] result=@HandlerExecutionChain[
        logger=@SLF4JLocationAwareLog[org.apache.commons.logging.impl.SLF4JLocationAwareLog@665c08a],
        handler=@HandlerMethod[public com.example.demo.arthas.user.User com.example.demo.arthas.user.UserController.findUserById(java.lang.Integer)],
        interceptors=null,
        interceptorList=@ArrayList[isEmpty=false;size=2],
        interceptorIndex=@Integer[-1],
    ]

可以看到处理请求的handler是 `om.example.demo.arthas.user.UserController.findUserById`。

## 总结 ##

*  Spring MVC的请求是在`DispatcherServlet`分发，查找到对应的`mappedHandler`来处理
 *  使用Arthas时，灵活结合代码，可以快速精确定位问题

## 链接 ##

*  [https://github.com/alibaba/arthas][https_github.com_alibaba_arthas]
 *  [https://alibaba.github.io/arthas/watch.html][https_alibaba.github.io_arthas_watch.html]
 *  [https://alibaba.github.io/arthas/trace.html][https_alibaba.github.io_arthas_trace.html]

## 公众号 ##

欢迎关注横云断岭的专栏，专注Java，Spring Boot，Arthas，Dubbo。

![横云断岭的专栏][qrcode_gongzhonghao.jpg]

转载于:https://my.oschina.net/hengyunabc/blog/3058657

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220113/76c9a08bc46a48a5b5413caefdb9d6db.png
[https_github.com_alibaba_arthas]: https://github.com/alibaba/arthas
[Arthas]: https://alibaba.github.io/arthas/arthas-tutorials?language=cn
[http_hengyunabc.github.io_arthas-spring-boot-404-401]: http://hengyunabc.github.io/arthas-spring-boot-404-401/
[https_github.com_hengyunabc_spring-boot-inside_tree_master_demo-404-401]: https://github.com/hengyunabc/spring-boot-inside/tree/master/demo-404-401
[http_localhost_8080_user_1]: http://localhost:8080/user/1
[https_alibaba.github.io_arthas_watch.html]: https://alibaba.github.io/arthas/watch.html
[https_alibaba.github.io_arthas_trace.html]: https://alibaba.github.io/arthas/trace.html
[qrcode_gongzhonghao.jpg]: /images/20220113/bbb23ca3ca2f4872b8922cf90efdea62.png