Struts Hibernate 异常 list action

Question

java.lang.NullPointerException
org.apache.jsp.zhuanye.listZY_jsp._jspService(org.apache.jsp.zhuanye.listZY_jsp:131)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:99)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:325)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1062)
org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:386)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:229)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

Answer 1

type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:373)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:291)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1062)
org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:386)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:229)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

Answer 2

public class ZhuanyeAction extends BaseAction{
public ActionForward add(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) {
List<Zhuanye> list = null;
CollegeService collService =new CollegeService();
list=collService.findAll();
request.setAttribute("collegeList",list);
ActionForward forward = mapping.findForward("add");
return forward;
}
public ActionForward list(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response) {
ZYService zys = new ZYService();
List<Zhuanye> list =zys.findAll();
request.setAttribute("zyList", list);
return mapping.findForward("list");
}
public ActionForward insert(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response){
ActionMessages messages = new ActionMessages();
//ActionErrors errors =new ActionErrors();// 过期改用messages
ZhuanyeForm zForm =(ZhuanyeForm)form;
Zhuanye zy = new Zhuanye();
//格式化字符 转换编码
String zyid =(String)zForm.getZhuanyeId();
if (zyid ==null)
{messages.add(ActionMessages.GLOBAL_MESSAGE, new ActionMessage(
"zhuanye.message.add.fail"));
saveErrors(request, messages);
request.setAttribute("zhuanyeFormBean", zForm);
return mapping.findForward("add");
}else{
//zyid =new String(zyid.getBytes("ISO-8859-1"),"UTF-8");
//中文乱码未解决
ZYService zys = new ZYService();
zy.setZhuanyeId(zyid);
zy.setCollege(zForm.getCollege());
zy.setZyname(zForm.getZyname());
zys.save(zy);
List<Zhuanye> list2 =zys.findAll();
request.setAttribute("zyList",list2); return list(mapping,form,request,response);
}

}
public ActionForward update(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response){
String id = (String)request.getParameter("zhuanyeId");
ZYService zys = new ZYService();
Zhuanye zy =null;
zy= zys.findById(id);
request.setAttribute("zy", zy);
return mapping.findForward("update");
}
public ActionForward saveUpdate(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response){
ZhuanyeForm zForm =(ZhuanyeForm)form;
ZYService zys = new ZYService();
String id = (String)request.getParameter("zhuanyeId");
Zhuanye zy =null;
zy= zys.findById(id);
zy.setZhuanyeId(id);
zy.setCollege(zForm.getCollege());
zy.setZyname(zForm.getZyname());
zys.save(zy);
return list(mapping, form, request, response);
}
public ActionForward delete(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response){
String id = (String)request.getParameter("zhuanyeId");
ZYService zys = new ZYService();
Zhuanye zy =null;
zy= zys.findById(id);
zys.delete(zy);
List list = zys.findAll();
request.setAttribute("zyList", list);
return list(mapping, form, request, response);
}
}

Answer 3

页面代码如下 zylist.jsp
<%@ page language="java" pageEncoding="UTF-8"%><%@ taglib uri="http://struts.apache.org/tags-bean" prefix="bean" %>
<%@ taglib uri="http://struts.apache.org/tags-html" prefix="html" %>
<%@ taglib uri="http://struts.apache.org/tags-logic" prefix="logic" %>
<%@ taglib uri="http://struts.apache.org/tags-tiles" prefix="tiles" %><%@ page import="com.study.domain.Zhuanye"%>
<%@ page import="java.util.List"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html:html lang="true">
  <head>
    <html:base />
    
    <title>listZY.jsp</title> <meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">    
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->  </head>
  <%
List list = (List) request.getAttribute("zyList"); %>
  <body>
   <table width="100%" bgcolor="#D9EBBE">
   <tr>
   <td>当前位置：专业管理</td>
   <td align="right"><a href="/T10/zhuanye.do?method=add">新增专业</a></td>
   <td width="20"></td>
   
   </tr>
   
   </table>
   <table width="80%"  border="0" align="center" cellpadding="0" cellspacing="1" bgcolor="blue">
<tr bgcolor="#D9EBBE">
<td width="20%" >专业编号</td>
<td width="20%" >专业名称</td>
<td width="40%" >所属学院</td>
<td width="20%">操作</td>
</tr>
<%if (list != null) {
for (int i = 0; i < list.size(); i++) {
Zhuanye zy = (Zhuanye) list.get(i);
%>
<tr bgcolor="#FFFFFF">
<td width="20%"><%=zy.getZhuanyeId()%>&nbsp;</td>
<td width="20%"><%=zy.getZyname()%>&nbsp;</td>
<td width="40%"><%=zy.getCollege().getCollegeName()%>&nbsp;</td>
<td width="20%">
   <a href="/T10/zhuanye.do?method=update&collegeId=<%=zy.getZhuanyeId()%>">修改</a>
   <a href="/T10/zhuanye.do?method=delete&collegeId=<%=zy.getZhuanyeId()%>">删除</a></td>
</tr>
<%}
}%>
  </body>
</html:html>

Answer 4

第一，在页面中尽量不要包含JAVA代码
第二. 
<% 
List list = (List) request.getAttribute("zyList"); 
%>
当zyList为空，页面会抛出此异常，对以个空的对象强制转型会出现此问题td width="20%"> <%=zy.getZhuanyeId()%>&nbsp; </td> 
<td width="20%"> <%=zy.getZyname()%>&nbsp; </td> 
<td width="40%"> <%=zy.getCollege().getCollegeName()%>&nbsp; </td> 
<td width="20%"> 
  <a href="/T10/zhuanye.do?method=update&collegeId= <%=zy.getZhuanyeId()%>">修改 </a> 
  <a href="/T10/zhuanye.do?method=delete&collegeId= <%=zy.getZhuanyeId()%>">删除 </a> </td> 
就是zyList不为空，zyList里某个对象的某个字段为空同样会抛出此异常，建议使用el表达式或者struts标签来显示数据