tomcat 根目录泻露如何防止?

Question

Tomcat---web.xml---(Warning:it's Tomcat's web.xml)
......
<servlet>
    <servlet-name>default</servlet-name>
    <servlet-class>org.apache.catalina.servlets.DefaultServlet</servlet-class>
    <init-param>
      <param-name>debug</param-name>
      <param-value>0</param-value>
    </init-param>
    <init-param>
      <param-name>listings</param-name>   ----OK----
      <param-value>false</param-value>   ----true->false---
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>