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arthas/tutorials/katacoda/arthas-advanced-cn/case-http-404.md

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在这个案例里展示排查HTTP 404问题的技巧。
访问: https://[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com/a.txt
结果是:
```
Something went wrong: 404 Not Found
```
那么到底是哪个Servlet处理了这个请求返回了404
### 跟踪所有的Servlet函数
开始trace
`trace javax.servlet.Servlet * > /tmp/servlet.txt`{{execute T2}}
访问: https://[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com/a.txt
在`Terminal 3`里,查看`/tmp/servlet.txt`的内容:
`less /tmp/servlet.txt`{{execute T3}}
`/tmp/servlet.txt`里的内容会比较多,需要耐心找到调用树里最长的地方。
可以发现请求最终是被`freemarker`处理的:
```
`---[13.974188ms] org.springframework.web.servlet.ViewResolver:resolveViewName()
+---[0.045561ms] javax.servlet.GenericServlet:<init>()
+---[min=0.045545ms,max=0.074342ms,total=0.119887ms,count=2] org.springframework.web.servlet.view.freemarker.FreeMarkerView$GenericServletAdapter:<init>()
+---[0.170895ms] javax.servlet.GenericServlet:init()
| `---[0.068578ms] javax.servlet.GenericServlet:init()
| `---[0.021793ms] javax.servlet.GenericServlet:init()
`---[0.164035ms] javax.servlet.GenericServlet:getServletContext()
```