我是初学者，我使用jsp servlet和hibernate，我想将对象从servlet传递给jsp
基本上我想用id输出当前的Faculty及其各自的名字。
这是我的编程：
package com.college;
import com.college.faculty.Faculty;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.Iterator;
import java.util.List;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
public class FacultyExtract extends HttpServlet {
SessionFactory factory;
public void init(ServletConfig config ) throws ServletException
{
factory = new Configuration().configure().buildSessionFactory();
System.out.println("Factory has been created");
}
public void service(ServletRequest request,ServletResponse response)throws ServletException,IOException
{
//HttpSession obses = request.getSession();
int pageIndex=0;
int totalNumberOfRecords=0;
int numberOfRecordsPerPage=4;
String sPageIndex= request.getParameter("pageIndex");
if(sPageIndex==null)
{
pageIndex=1;
}
else
{
pageIndex = Integer.parseInt(sPageIndex);
}
Session ses = factory.openSession();
int s= ( pageIndex*numberOfRecordsPerPage)-numberOfRecordsPerPage;
Criteria crit = ses.createCriteria(Faculty.class);
crit.setFirstResult(s);
crit.setMaxResults(numberOfRecordsPerPage);
List l= crit.list();
Iterator it =l.iterator();
for (int i=1;i>=6;i++)
{
Faculty m = (Faculty)it.next();
if( i==1 )
{
Faculty a1 = (Faculty) m ;
request.setAttribute("F1",a1);
}
if( i==2 )
{ Faculty a2 = (Faculty) m ;
request.setAttribute("F2",a2);
}
if( i==3 )
{ Faculty a3 = (Faculty) m ;
request.setAttribute("F3",a3);
}
if( i==4 )
{
Faculty a4 = (Faculty) m ;
request.setAttribute("F4",a4);
}
if( i==5 )
{
Faculty a5 = (Faculty) m ;
request.setAttribute("F5",a5);
}
if( i==6 )
{
Faculty a6 = (Faculty) m ;
request.setAttribute("F6",a6);
}
}
RequestDispatcher dispatcher = request.getRequestDispatcher("Faculty.jsp");
dispatcher.forward(request , response);
}
}
Faculty.jsp
<%@page import="com.college.faculty.Faculty"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<%
//HttpSession obses=request.getSession();
Faculty fac =(Faculty) request.getAttribute("f1");
// System.out.println(fac.getExpDetail());
//String f2 = (String)fac.getQulification();
%>
<h1>Hello World!</h1>
<%=fac.getExpDetail()%>
</body>
</html>
错误代码：
HTTP Status 500 - java.lang.NullPointerException
type Exception report
message java.lang.NullPointerException
description The server encountered an internal error that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:5 49)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:470)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:403)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:347)
javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
com.college.FacultyExtract.service(FacultyExtract.java:116)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
root cause
java.lang.NullPointerException
org.apache.jsp.Faculty_jsp._jspService(Faculty_jsp.java:90)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:403)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:347)
javax.servlet.http.HttpServlet.service(HttpServlet.java:725)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
com.college.FacultyExtract.service(FacultyExtract.java:116)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
note The full stack trace of the root cause is available in the Apache Tomcat/8.0.3 logs.
faculty.java
package com.college.faculty;
public class Faculty {
private int fid;
private String fname;
private String qulification;
private String expDetail;
public void setFacQul(int fid,String fname,String qulification,String expDetail)
{
this.fid = fid;
this.fname = fname;
this.qulification = qulification;
this.expDetail = expDetail;
}
public int getFid() {
return fid;
}
public void setFid(int fid) {
this.fid = fid;
}
public String getFname() {
return fname;
}
public void setFname(String fname) {
this.fname = fname;
}
public String getQulification() {
return qulification;
}
public void setQulification(String qulification) {
this.qulification = qulification;
}
public String getExpDetail() {
return expDetail;
}
public void setExpDetail(String expDetail) {
this.expDetail = expDetail;
}
}
答案 0 :(得分：1)
您在servlet中使用大写“F1”，在jsp“f1”中使用小写。它必须是一样的。最好定义具有常量的接口，例如属性名称区分大小写。
//servlet
request.setAttribute("F1",a1); //upper
//jsp
Faculty fac =(Faculty) request.getAttribute("f1"); // lower
还有Si Kelly指出的错误：
“你的循环中有错误：for（int i = 1; i＆gt; = 6; i ++） - 这永远不会进入因为我从来没有＆gt; = 6 - Si Kelly”
应该是（int i = 1; i.hasNext（）; i ++）或者如果集合中的元素少于6，则会有异常。