当我尝试从 Java 类获取值到 JSP 时，我的 JSP 显示“nul”
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When I try to get value from Java class to JSP, my JSP shows "nul"
提问by
I am till a learner in Java, please help me out. Here is my sample code, when I execute this program. It should retrieve info from the data base and store the values in the Java class and there by send the value to JSPbut when i look at JSPit shows value "null"
我是 Java 的学习者，请帮帮我。这是我执行此程序时的示例代码。它应该从数据库中检索信息并将值存储在 Java 类中，然后将值发送到，JSP但是当我查看JSP它时显示值“null”
Here are the 5 files related to my problem, any answers or solutions are happily accepted.
这是与我的问题相关的 5 个文件，任何答案或解决方案都被愉快地接受。
-------------------------this my basic input form---------------------------
-------------------------这是我的基本输入表单-------------------- -------
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>WELCOME TO DISCOUNTLOVERS.IN</title>
<script type="text/javascript" src="jquery-1.2.6.min.js"></script>
<link href="stylesheet.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div id="wrapper">
<div><%@include file="header.jsp" %></div>
<div><table width="920" border="0" cellpadding="0" cellspacing="0" id="main-content" >
<form method ="post" action ="Registrationform" >
<tbody>
<tr>
<td width="382" valign="top" class="formtext">
<div>First Name</div>
<div>Last name</div>
<div>E-mail</div>
<div>Password</div>
<div>Confirm Password</div>
<div>phone no</div>
<div>Address</div>
<div>City</div>
<div>State</div>
<div>country</div>
<div>post code</div>
</td>
<td width="52" class="formtext-gap">
<div>:</div>
<div>:</div>
<div>:</div>
<div>:</div>
<div>:</div>
<div>:</div>
<div>:</div>
<div>:</div>
<div>:</div>
<div>:</div>
<div>:</div>
</td>
<td width="486" valign="top">
<div><input type="text" name="username_first"/></div>
<div><input type="text" name="username_last"/></div>
<div><input type="text" name="username_email"/></div>
<div><input type="text" name="username_pw"/></div>
<div><input type="text" name="username_cpw"/></div>
<div><input type="text" name="username_tele"/></div>
<div><input type="text" name="username_add"/></div>
<div><input type="text" name="username_city"/></div>
<div><input type="text" name="username_state"/></div>
<div><input type="text" name="username_country"/></div>
<div><input type="text" name="username_postcode"/></div>
</td>
</tr>
<tr><td colspan="3" align="center"><input type="checkbox"/> Terms and conditions of Discountlovers.in accpeted</td></tr>
<tr><td colspan="3" align="center"><div><input type="submit" value="Submit" class=""/></div></td></tr>
</tbody></form></table></div>
<div><%@include file="footer.jsp" %></div>
</div>
</body>
</html>
------------------------ this is data insertion servlet------------------------
------------------------ 这是数据插入servlet--------------------- ---
package registration_Servlets;
import registration_Servlets.intialization_form;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.PreparedStatement;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class Registrationform
*/
@WebServlet("/Registrationform")
public class Registrationform extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public Registrationform() {
super();
// TODO Auto-generated constructor stub
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter pw = response.getWriter();
intialization_form obj = new intialization_form();
String name;
String lastname;
String username_email;
String username_pw ;
String username_cpw;
String id ;
String username_add;
String username_city ;
String username_state;
String username_country;
String username_postcode;
try {
name = request.getParameter("username_first");
lastname = request.getParameter("username_last");
username_email = request.getParameter("username_email");
username_pw = request.getParameter("username_pw");
username_cpw = request.getParameter("username_cpw");
id = request.getParameter("username_tele");
username_add = request.getParameter("username_add");
username_city = request.getParameter("username_city");
username_state = request.getParameter("username_state");
username_country = request.getParameter("username_country");
username_postcode = request.getParameter("username_postcode");
DataBase db = new DataBase();
PreparedStatement pst = db.getConnection().prepareStatement("insert into registrationinfo values(?,?,?,?,?,?,?,?,?,?,?)");
pst.setString(1, name );
pst.setString(2, lastname);
pst.setString(3, username_email);
pst.setString(4, username_pw);
pst.setString(5, username_cpw);
pst.setString(6, id);
pst.setString(7, username_add);
pst.setString(8, username_city);
pst.setString(9, username_state);
pst.setString(10, username_country);
pst.setString(11, username_postcode);
int i = pst.executeUpdate();
if(i==1){
//request.setAttribute("name",name);
/*String site = new String("Retrivin_user_reg_form");
response.setStatus(response.SC_MOVED_TEMPORARILY);
response.setHeader("Location", site); */
response.sendRedirect("Retrivin_user_reg_form");
}
pw.println("done");
}
catch (Exception e) {
e.printStackTrace();
}
}
}
--------------------------------this is my data retrieve servlet-----------------
--------------------------------这是我的数据检索servlet------------ -----
package registration_Servlets;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class Retrivin_user_reg_form
*/
@WebServlet("/Retrivin_user_reg_form")
public class Retrivin_user_reg_form extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public Retrivin_user_reg_form() {
super();
// TODO Auto-generated constructor stub
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter pw = response.getWriter();
try {
DataBase db = new DataBase();
PreparedStatement pst = db.getConnection().prepareStatement("Select * from registrationinfo");
intialization_form obj = new intialization_form();
ResultSet i = pst.executeQuery();
while(i.next()){
// pw.println("EmpName" + " " + "EmpSalary" + "<br>");
obj.name= i.getString(1);
obj.lastname=i.getString(2);
obj.username_email=i.getString(3);
obj.username_pw=i.getString(4);
obj.username_cpw=i.getString(5);
obj.id=i.getString(6);
obj.username_add=i.getString(7);
obj.username_city=i.getString(8);
obj.username_state=i.getString(9);
obj.username_country=i.getString(10);
obj.username_postcode=i.getString(11);
String site = new String("registrationcompleted.jsp");
response.setStatus(response.SC_MOVED_TEMPORARILY);
response.setHeader("Location", site);
/*request.getRequestDispatcher("registrationcompleted.jsp").forward(request, response);*/
}
}
catch (Exception e) {
e.printStackTrace();
}
}
protected void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
}
}
-----------this is my Java class where i want to store my retrieved data--------------
-----------这是我的 Java 类，我想在其中存储检索到的数据--------------
package registration_Servlets;
public class intialization_form
{
String name;
String lastname;
String username_email;
String username_pw;
String username_cpw;
String id;
String username_add;
String username_city;
String username_state;
String username_country;
String username_postcode;
public void setname( String value )
{
name = value;
}
public String getname() { return name; }
public void setlastname( String value )
{
lastname = value;
}
public String getlastname() { return lastname; }
public void setusername_email( String value )
{
username_email = value;
}
public String getusername_email() { return username_email; }
public void setusername_pw(String value){
username_pw= value;
}
public String getusername_pw() { return username_pw; }
public void setusername_cpw(String value){
username_cpw=value;
}
public String getusername_cpw(){
return username_cpw;
}
public void setid(String value){
id= value;
}
public String getid(){
return id;
}
public void setusername_add(String value){
username_add= value;
}
public String getusername_add(){
return username_add;
}
public void setusername_city(String value){
username_city= value;
}
public String getusername_city(){
return username_city;
}
public void setusername_state(String value){
username_state= value;
}
public String getusername_state(){
return username_state;
}
public void setusername_country(String value){
username_country = value;
}
public String getusername_country(){
return username_country;
}
public void setusername_postcode(String value){
username_postcode= value;
}
public String getusername_postcode(){
return username_postcode;
}
}
-------------------------this is my out put JSP where I get null value-------------
-------------------------这是我得到空值的输出 JSP -------------
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import = "registration_Servlets.intialization_form" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>WELCOME TO DISCOUNTLOVERS.IN</title>
<script type="text/javascript" src="jquery-1.2.6.min.js"></script>
<link href="stylesheet.css" rel="stylesheet" type="text/css" />
</head>
<body>
<div id="wrapper">
<div><%@include file="header.jsp" %></div>
<div><table width="920" border="0" cellpadding="0" cellspacing="0" id="main-content">
<tbody>
<tr>
<td>
<% intialization_form user = new intialization_form(); %>
first Name: <%= user.getname() %>
last name: <%= user.getlastname() %><BR>
Email: <%= user.getusername_email() %><BR>
</td>
</tr>
</tbody></table></div>
<div><%@include file="footer.jsp" %></div>
</div>
</body>
</html>
采纳答案by Kartik73
I can see you have used
我看你用过
request.getRequestDispatcher("registrationcompleted.jsp").forward(request, response);
before doing this add line given below before forward()method
在执行下面给出的forward()方法之前的添加行之前
request.setAttribute("your-key", yourObjectReference);
This method of requestobject will set your form objectas an attribute which you want to access in your output jsp, which you can retrieve using request.getAttribute("key")method.
这个request对象的方法将设置your form object为您要在您的 中访问的属性output jsp，您可以使用request.getAttribute("key")方法检索该属性。
put below code in your output jsp.
把下面的代码放在你的输出jsp中。
<% intialization_form user = (intialization_form)request.getAttribute("your-key"); %>
since request.getAttribute()method returns Objectyou will have to cast it in intialization_form
由于request.getAttribute()方法返回，Object您将不得不将其转换为intialization_form
And don't forget to remove below lines from your code before doing this
并且在执行此操作之前不要忘记从代码中删除以下行
response.setStatus(response.SC_MOVED_TEMPORARILY);
response.setHeader("Location", site);
回答by Ralph
It is because the values in you form class are NULL. You never assign any values to them.
这是因为您表单类中的值是 NULL。您永远不会为它们分配任何值。
You just create an empty form object and the "print" some of its values.
您只需创建一个空的表单对象并“打印”它的一些值。
<% intialization_form user = new intialization_form(); %>
first Name: <%= user.getname() %>
last name: <%= user.getlastname() %><BR>
Email: <%= user.getusername_email() %><BR>
@See https://stackoverflow.com/tags/servlets/infofor some info how to start jsp and servlet programming.
@有关如何启动 jsp 和 servlet 编程的一些信息，请参阅https://stackoverflow.com/tags/servlets/info。
