org.springframework.web.servlet.PageNotFound - No mapping found for HTTP request with URI [“”] in DispatcherServlet with name 'springMVC'

Spring前端控制器的问题，在web.xml下，一开始的配置是：

 <servlet-mapping>
    <servlet-name>SpringMVC</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

根据网友建议改成 

<servlet-mapping>
    <servlet-name>SpringMVC</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>

后依然报这个错，改成 

<servlet-mapping>
    <servlet-name>SpringMVC</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>

不再报错，暂时不知道原因