问题描述
今天在开发中遇到一奇怪问题，有一个action，在该action里使用request.setAttribute()方法将一个List类型对象放在request中，然后forward到一个jsp文件，该文件的主要内容是使用<logic:iterate>标签将这个List对象中的条目列表显示。与它同样逻辑但位于另一模块（teacher）中的代码执行正常。但这个模块（xxgl）中的代码，本来很简单的逻辑，却总是提示：
org.apache.jasper.JasperException: Cannot find bean t in any scope at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:254) at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295) at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241) at javax.servlet.http.HttpServlet.service(HttpServlet.java:853) at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:684) at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:432) at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:356) at org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1069) at org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:455) at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:279) at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482) at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:507) at javax.servlet.http.HttpServlet.service(HttpServlet.java:740) at javax.servlet.http.HttpServlet.service(HttpServlet.java:853) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995) at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2417) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643) at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:172) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174) at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480) at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995) at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:193) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:781) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:549) at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:589) at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:666) at java.lang.Thread.run(Unknown Source) 将<logic:iterate>之间的代码去掉后就不会提示错误了，所以怀疑是<bean:write>中的代码有错误。相关文件ListSfzxJbxxAction.java中的execute方法如下：
public ActionForward execute( ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { HibernateDAO dao = HibernateDAO.getInstance(getServlet().getServletContext()); List sfzxjbxxs = dao.find("from " + SfzxJbxx.class.getName()); SfzxJbxx tmp = new SfzxJbxx(); tmp.setSfzxid("id"); tmp.setXxdm("pku"); sfzxjbxxs.add(tmp); request.setAttribute("sfzxjbxxs", sfzxjbxxs); return mapping.findForward("success"); } listsfzxjbxx.jsp内容如下：
<%
@ page contentType="text/html;charset=UTF-8" language="java" %> <%@ taglib uri="/WEB-INF/struts-bean.tld" prefix="bean"%> <%@ taglib uri="/WEB-INF/struts-html.tld" prefix="html"%> <head> <title>SfzxJbxxList</title> </head> <body> <logic:iterate name="sfzxjbxxs" id="sfzxjbxx"> <tr> <td align="left"> <bean:write name="sfzxjbxx" property="sfzxId" filter="true"/> </td> <td align="left"> <bean:write name="sfzxjbxx" property="xxdm" filter="true"/> </td> <td> </td> </tr> </logic:iterate> <body> </html> 模块配置文件中相关内容如下：
<action-mappings> <action attribute="Form" input="/form/sfzxjbxx.jsp" name="sfzxJbxxForm" path="/saveSfzxJbxx" type="edu.pku.cc.sfzx.xxgl.action.SaveSfzxJbxxAction" /> <action path="/listsfzxjbxx" type="edu.pku.cc.sfzx.xxgl.action.ListSfzxJbxxAction"> <forward name="success" path="/form/listsfzxjbxx.jsp"/> </action> </action-mappings> 问题解决
经过三个小时的检查，发现是listsfzxjbxx.jsp里缺少<logic:iterate>标签的声明，在前面增加上：
<%@ taglib uri="/WEB-INF/struts-logic.tld" prefix="logic"%> 一切OK！