java.lang.NullPointerException: Module 'null' not found.

 

严重: 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:108)
	at org.apache.jsp.index_jsp._jspService(index_jsp.java:75)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	at org.apache.jasper.servlet.Jspjava.lang.NullPointerException: Module 'null' not found.ServletWrapper.service(JspServletWrapper.java:393)
	at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320)
	at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:266)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:230)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
	at java.lang.Thread.run(Thread.java:619)

 

 

 

异常起源：

 

一、初学Struts时 手动配置Struts的各项环境需求。并且想在index.jsp中手写<html:text>等Struts标签

在Struts-config.xml 配置好了一切之后，配置web.xml的Struts ActionServlet 代码如下：

 

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

 

 

二、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

 

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>

 

     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