使用struts的java中出现空指针异常错误
我试图从数据库中检索数据,但在struts中出现空指针异常。我正在使用ecllipse mars 提前谢谢 我的档案是:- web.xml使用struts的java中出现空指针异常错误,java,nullpointerexception,Java,Nullpointerexception,我试图从数据库中检索数据,但在struts中出现空指针异常。我正在使用ecllipse mars 提前谢谢 我的档案是:- web.xml enter code here <?xml version="1.0" encoding="UTF-8"?> <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:sche
enter code here
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/javaee"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
<display-name>Report2</display-name>
<filter>
<filter-name>struts2</filter-name>
<filter-class>
org.apache.struts2.dispatcher.FilterDispatcher
</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE struts PUBLIC
"-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
"http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<constant name="struts.enable.DynamicMethodInvocation" value="false" />
<constant name="struts.devMode" value="false" />
<constant name="struts.custom.i18n.resources" value="myapp" />
<package name="default" extends="struts-default" namespace="/">
<action name="database" class="genius.database.ReportAction"
method="execute">
<result name="Success">/ReportView.jsp</result>
</action>
</package>
</struts>
ReportView.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@taglib prefix="s" uri="/struts-tags" %>
<%@page language="java" import="java.util.*" %>
<%@page language="java" import="genius.database.Student" %>
<%@page language="java" import="genius.database.ReportAction" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<h2>Report</h2>
<s:actionerror key="error.Insert"/>
<s:form name="form" method="post">
<table border="1">
<thead>
<tr>
<td>Roll No</td>
<td>Name</td>
<td>Eng</td>
<td>Maths</td>
</tr>
</thead>
<tbody>
<tr>
<%
List<Student> li=(List<Student>)request.getAttribute("disp");
out.println(li);
if(li==null){
Iterator<Student> it=li.iterator();
while(it.hasNext()){
Student st=(Student)it.next();
int rno=st.getRno();
String name=st.getName();
int eng=st.getEng();
int mat=st.getMaths();
%>
<td><%out.println(rno);%></td>
<td><%out.println(name);%></td>
<td><%out.println(eng);%></td>
<td><%out.println(mat);%></td>
<% }
}
%>
</tr>
</tbody>
</table>
</s:form>
</body>
</html>
在此处插入标题
报告
卷号
名称
英格
数学
index.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Report</title>
</head>
<body>
<s:form action="database.action">
<s:submit value="Submit"></s:submit>
</s:form>
</body>
</html>
报告
你的意思可能是:
if (li!=null)
从
if(li==null){
迭代器it=li.Iterator();
while(it.hasNext()){
Student st=(Student)it.next();
int rno=st.getRno();
String name=st.getName();
int eng=圣赫滕();
int mat=st.GetMath();
不确定是否是这样,但这肯定会导致NullPointerException。最好在JSP中使用JSTL而不是scriplets e、 g
....
${student.rno}
${student.name}
请参见您是否有异常的stacktrace?我也会发布它。这通常是关于从何处开始查找的最佳信息。
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@taglib prefix="s" uri="/struts-tags" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Report</title>
</head>
<body>
<s:form action="database.action">
<s:submit value="Submit"></s:submit>
</s:form>
</body>
</html>
if (li!=null)
if(li==null){
Iterator<Student> it=li.iterator();
while(it.hasNext()){
Student st=(Student)it.next();
int rno=st.getRno();
String name=st.getName();
int eng=st.getEng();
int mat=st.getMaths();
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
....
<c:forEach items="${disp}" var="student" >
${student.rno}
${student.name}
</c:forEach>