Question

我想使用jsp从数据库中检索数据并将其显示在jsp上。我尝试使用jsp和servlet并且它正在工作，但是当我只想使用jsp时它会给出这个错误。

retrieve.jsp：

<%@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>
    <h4>Enter Employee ID and the dates</h4>
    <form name="retrieve form" action="display.jsp" method="POST">
        <table border="0">

            <tbody>
                <tr>
                    <td>Employee ID</td>
                    <td><input type="text" name="Emp_id" required="required"/></td>
                </tr>
                <tr>
                    <td>From Date:</td>
                    <td><input type="date" name="From" value="yyyy/MM/dd" required="required"/></td>
                </tr>
                <tr>
                    <td>To Date:</td>
                    <td><input type="date" name="To" value="yyyy/MM/dd" required="required"/></td>
                </tr>
            </tbody>
        </table>
        <input type="reset" value="Clear" name="clear" />
        <input type="submit" value="Submit" name="submit" />
    </form>
</body>
</html>

Display.jsp：

<%@page import="java.sql.*"%>
<%@page import="com.eis.bean.ConnectionProvider" %>
<%@page import="com.eis.bean.Provider" %>
<%@page import="java.util.Date"%> 

<%@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>
    <%! 
        public class RD{


        PreparedStatement ps = null; 
        ResultSet rs = null;
        public RD(){
           try{ 
        Connection conn=ConnectionProvider.getConn();  
        ps = conn.prepareStatement("SELECT * FROM timsheetdb.logintable WHERE Emp_id=? and LoginDate BETWEEN ? AND ?; ");  

           }
           catch(Exception e){
               e.printStackTrace();
           }
        }

        public ResultSet getRD(String Emp_id, String from, String to){
            try{
                ps.setString(1,Emp_id);
                ps.setString(2,from);
                ps.setString(3,to);

            }
            catch(Exception e){
               e.printStackTrace();
           }   
            return rs;
        }
        }
%>
<% String employeeid= new String();
 String date1= new String();
 String date2= new String();

 if(request.getParameter("Emp_id")!=null){
     employeeid= request.getParameter("Emp_id");
 }

 if(request.getParameter("from")!=null){
     date1= request.getParameter("from");
 }

 if(request.getParameter("to")!=null){
     date2= request.getParameter("to");
 }

 RD rd= new RD();
 ResultSet table= rd.getRD(employeeid,date1,date2);
    %>
   <table border="0">
            <tbody>
                <tr>
                    <td>Emp_id</td>
                    <td>Login Date</td>
                    <td>Login Time</td>
                    <td>Logout Time</td>
                    <td>Task</td>
                    <td>Total</td>
                    <td>Overtime</td>
                </tr>
                <% while (table.next()){ 
               %> <tr>
                    <td><%=table.getString("Emp_id") %></td>
                    <td><%=table.getString("LoginDate") %></td>
                    <td><%=table.getString("LoginTime") %></td>
                    <td><%=table.getString("LogoutTime") %></td>
                    <td><%=table.getString("task") %></td>
                    <td><%=table.getString("Total") %></td>
                    <td><%=table.getString("Overtime") %></td>
                </tr>
                <% } %>
            </tbody>
        </table>
</body>
</html>

下面是我得到的错误：

HTTP Status 500 - An exception occurred processing JSP page /display.jsp at line 80

type Exception report

message An exception occurred processing JSP page /display.jsp at line 80

description The server encountered an internal error that prevented it from  fulfilling this request.

exception

org.apache.jasper.JasperException: An exception occurred processing JSP page     /display.jsp at line 80

77:                         <td>Total</td>
78:                         <td>Overtime</td>
79:                     </tr>
80:                     <% while (rs.next()){ 
81:                    %> <tr>
82:                         <td><%=rs.getString("Emp_id") %></td>
83:                         <td><%=rs.getString("LoginDate") %></td>
Stacktrace:
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:574)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:476)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause

java.lang.NullPointerException
org.apache.jsp.display_jsp._jspService(display_jsp.java:178)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:438)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:396)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:340)
javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
note The full stack trace of the root cause is available in the Apache      Tomcat/8.0.26 logs.

请让我知道如何解决这个问题。

Answer 1

80:                     <% while (rs.next()){

和

<% while (table.next()){

那里不一样，也许你没有部署最新版本的代码。

但总而言之是错误

java.lang.NullPointerException

你需要在使用之前检查是否设置了rs（或表）。

if(rs!=null)

和We are borg一样，不要在jsp中执行sql，只是不要。

Answer 2

像这样改变你的方法

public ResultSet getRD(String Emp_id, String from, String to){
                try{
                    ps.setString(1,Emp_id);
                    ps.setString(2,from);
                    ps.setString(3,to);
                    rs = ps.executeQuery();
                }
                catch(Exception e){
                   e.printStackTrace();
               }   
                return rs;
            }

之前你只是在准备好的语句中设置参数而你没有执行准备好的语句。你只是返回rs，你最初保持为null并且从未在你的代码中更新。说明为什么它失败了nullpointerexception 。我希望它会给你一个指向正确方向的指针。

使用jsp从数据库中检索数据

2 个答案: