关于java.lang.NullPointerException: Module 'null' not found.的问题

在用eclipse做struts1项目时，配置都ok了。可是一运行就报java.lang.NullPointerException: Module 'null' not found.错。

代码如下；

web.xml

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

struts-config.xml：

 <struts-config>
     <form-beans>
        <form-bean name="loginForm" type="com.actionform.LoginForm" />
     </form-beans>
     <action-mappings>
        <action path="/login" type="com.action.LoginAction" name="loginForm" input="/index.jsp"
            scope="request">
            <forward name="success" path="/success.jsp" />
        </action>
     </action-mappings>
 </struts-config>

jsp页面：

 <html:form action="login.do" method="post">
         <html:text property="username"></html:text>
         <br> <html:submit value="Submit"></html:submit>
 </html:form>

action和actionform都是ok的。

配置和好后，程序无任何语法异常。但是在我打开index.jsp页面的时候程序抛出了空指针异常

java.lang.NullPointerException: Module 'null' not found.抛出这个异常的时候我们知道这是由于Tomcat并未加载

ActionServlet 以致Jsp界面使用Struts中的<html:text property="">程序抛出异常.

 Oct 10, 2015 4:38:15 PM org.apache.catalina.core.StandardWrapperValve invoke
 SEVERE: Servlet.service() for servlet jsp threw exception
 java.lang.NullPointerException: Module 'null' not found.
     at org.apache.struts.taglib.TagUtils.getModuleConfig(TagUtils.java:755)
     at org.apache.struts.taglib.TagUtils.getModuleConfig(TagUtils.java:735)
     at org.apache.struts.taglib.html.FormTag.lookup(FormTag.java:818)
     at org.apache.struts.taglib.html.FormTag.doStartTag(FormTag.java:488)
     at org.apache.jsp.index_jsp._jspx_meth_html_005fform_005f0(index_jsp.java:83)
     at org.apache.jsp.index_jsp._jspService(index_jsp.java:54)
     at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
     at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
     at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
     at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
     at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
     at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
     at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
     at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
     at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:174)
     at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
     at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
     at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
     at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
     at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:874)
     at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
     at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
     at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
     at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:689)
     at java.lang.Thread.run(Unknown Source)

异常延伸：

一、这个异常就牵扯到web.xml  的<load-on-startup></load-on-startp>

二、那么这个标签有什么用了？

这个标签有着很重要的用途<load-on-startup>（在这里可以放置0-5之间的整数）</load-on-startp>

 <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>
         <load-on-startup>1</load-on-startup>
     </servlet>

三、0-5 是web容器控制Tomcat告诉Tomcat按怎样的顺序去执行init（）方法加载Servlet（程序中可能会有多个Serlvet)如果没有在web.xml中使用这个标签或者参数的为负数 那么Tomcat将不自动加载这个Servlet。上诉错误就是因

为没有在web.xml中配置<load-on-startup>标签

四、另外<load-on-startup>中的参数越小那么优先级也就越高