如何解决如何将参数从jsp页面发送到servlet，然后发送到jsp页面，然后发送到servlet？
我正在尝试制作一个登录表格。并希望changepass.java文件访问username参数。
应用程序的流程为： login.jsp-> LoginServlet-> AfterLogin.jsp-> ChangePass.jsp-> ChangePassword Servlet
为此，我尝试使用session和request dispatcher。
我能够将参数从login.jsp获取到ChangePass.jsp，但是之后changePassword servlet将无法访问它。
我的流程代码是：
- login.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">
<body>
<div align="center">
<form name="login" onsubmit="return onSubmit()" action="LoginServlet">
<h2 style="color:blue">Account Login</h2>
<table style="background-color:powderblue;border: 2px solid green;border-color:green;">
<tr><td>Enter User Name:</td><td><input type="text" name="username" minlength="6" required></td></tr>
<tr><td>Enter Pass Word:</td><td><input type="password" name="password" id="password" required></td></tr>
<tr><td colspan="2" align="center"><input type="submit" value="login"></td></tr>
</table>
<br>
<a href="FirstPage.html" class="btn btn-primary"><u>Home</u></a>
</form>
</div>
<%
String msg=(String) request.getAttribute("msg");
if(msg!=null){
%>
<p style="color:red"><%=msg%></p>
<%
}
%>
<script type="text/javascript">
function onSubmit(){
var y=document.login.password.value;
var passR=/^(?=.*\d)(?=.*[A-Z]).{6,20}$/;
if(!y.match(passR)){
alert("Password must contain at least one number and one UpperCase letter");
document.getElementById("password").focus();
}
}
</script>
</body>
</html>
- LoginServlet.java
package com.wipro.controller;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
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;
import javax.servlet.http.HttpSession;
import com.wipro.util.DButil;
/**
* Servlet implementation class LoginServlet
*/
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public LoginServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request,HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {
// TODO Auto-generated method stub
try{
Connection con=DButil.getConnection();
PrintWriter out=response.getWriter();
String username=request.getParameter("username");
String password=request.getParameter("password");
String sql="select * from user_table where username=? and password=?";
PreparedStatement st=con.prepareStatement(sql);
st.setString(1,username);
st.setString(2,password);
ResultSet rs=st.executeQuery();
if(rs.next()) {
HttpSession se=request.getSession();
se.setAttribute("username",username );
request.getRequestDispatcher("AfterLogin.jsp").include(request,response);
}
else {
request.setAttribute("msg","Invalid Credentials");
request.getRequestDispatcher("login.jsp").include(request,response);
}
}
catch(Exception e) {
e.printStackTrace();
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request,HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request,IOException {
// TODO Auto-generated method stub
doGet(request,response);
}
}
- AfterLogin.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<h1><font color=green> Welcome <%=session.getAttribute("username")%></font></h1>
<a href="ChangePass.jsp">Change Password</a>
</body>
</html>
- ChangePass.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<div align="center">
<form name="changePS" onsubmit="return onSubmit()" action="ChangePassword">
<%
String username=(String)session.getAttribute("username");
request.setAttribute("username",username);
%>
<h1><font color=green> Welcome <%=username%></font></h1>
<h2 style="color:blue">Change Password</h2>
<table style="background-color:powderblue;border: 2px solid green;border-color:green;">
<tr><td>Old Password:</td><td><input type="password" name="oldpwd" id="oldpwd" required></td></tr>
<tr><td>New Password:</td><td><input type="password" name="newpwd" id="newpwd" required></td></tr>
<tr><td>Confirm Password:</td><td><input type="password" name="confpwd" id="confpwd" required></td></tr>
<tr><td colspan="2" align="center"><input type="submit" value="login"></td></tr>
</table>
<br>
<a href="FirstPage.html" class="btn btn-primary"><u>Home</u></a>
</form>
</div>
<script type="text/javascript">
function onSubmit(){
y=document.changePS.oldpwd.value;
z=document.changePS.newpwd.value;
a=document.changePS.confpwd.value;
passR=/^(?=.*\d)(?=.*[A-Z]).{6,20}$/;
if(z != a){
alert("New Password and Confirm Password do not match");
document.getElementById("confpwd").focus();
return false;
}
if(!y.match(passR)){
alert("Old Password must contain at least one number,one UpperCase letters");
document.getElementById("oldpwd").focus();
return false;
}
if(!z.match(passR)){
alert("New Password must contain at least one number,one UpperCase letters");
document.getElementById("newpwd").focus();
return false;
}
return true;
}
</body>
</html>
- ChangePassword.java
package com.wipro.controller;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
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;
import javax.servlet.http.HttpSession;
import com.wipro.util.DButil;
/**
* Servlet implementation class ChangePassword
*/
@WebServlet("/ChangePassword")
public class ChangePassword extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public ChangePassword() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request,IOException {
// TODO Auto-generated method stub
try{
Connection con=DButil.getConnection();
PrintWriter out=response.getWriter();
String username = (String)request.getAttribute("username");
String password=request.getParameter("newPwd");
String sql="update user_table set password=? where username=?";
PreparedStatement st=con.prepareStatement(sql);
st.setString(1,username);
st.setString(2,password);
int rs=st.executeUpdate();
if(rs!=0) {
out.println("<h1><font color=green> Updated the password </font></h1>");
}
else {
out.println("<h1><font color=red> Sorry no username with this name </font></h1>"+username);
}
}
catch(Exception e) {
e.printStackTrace();
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request,response);
}
}
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