STRUTS分模块后出现Servlet action is not available

Question

WEB.XML
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.4" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee   http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 <jsp-config>
   
<taglib>
<taglib-uri>/jstl-c</taglib-uri>
<taglib-location>/WEB-INF/c.tld</taglib-location>
</taglib>

<taglib>
<taglib-uri>/jstl-sql</taglib-uri>
<taglib-location>/WEB-INF/sql.tld</taglib-location>
</taglib>
  </jsp-config>
  <servlet>
    <servlet-name>action</servlet-name>
    <servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
    <init-param>
      <param-name>config</param-name>
      <param-value>/WEB-INF/struts-config.xml</param-value>
    </init-param>
    <init-param>
      <param-name>config/user</param-name>
      <param-value>/WEB-INF/user/struts-config-user.xml</param-value>
    </init-param>
    <init-param>
      <param-name>config/commodity</param-name>
      <param-value>/WEB-INF/commodity/struts-config-commodity.xml</param-value>
    </init-param>
    <init-param>
      <param-name>config/buy</param-name>
      <param-value>/WEB-INF/buy/struts-config-buy.xml</param-value>
    </init-param>
    <init-param>
      <param-name>debug</param-name>
      <param-value>3</param-value>
    </init-param>
    <init-param>
      <param-name>detail</param-name>
      <param-value>3</param-value>
    </init-param>
    <load-on-startup>0</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>action</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>
</web-app>如果不添加后面3个struts-config模块，只有struts-config.xml就是正常的，添加之后就出现了Servlet action is not available问题，请问是怎么回事？