我设计了一个JSP登录页面和一个用于服务器端验证的相应servlet。当我单击登录页面上的提交按钮时，如果提供的凭据不匹配，则响应页面将再次显示登录页面，并显示添加的错误消息。但是，当我刷新该页面时，它仍然显示错误消息。另一方面，如果登录凭证匹配，则会显示欢迎页面，但是我无法销毁会话。也就是说，如果我点击浏览器的“后退”按钮，它会再次显示登录页面，但如果我再单击“前进”按钮，它会再次显示欢迎页面。
如果用户刷新该页面，我希望抑制登录页面上的错误消息。我还希望用户的会话无效，如果他通过浏览器的“后退”按钮再次显示登录页面，这样（除其他外）他不能使用“前进”按钮返回先前呈现的页面当他登录时对他说。如何修改我的代码以向应用程序提供这些行为？
这是我的代码：
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Login Application</title>
</head>
<body>
<form action="loginServlet" method="post">
User Login
<br>
User ID
<input type="text" name="username" >
<br><br>
Password
<input type="password" name="userpass"><br>
<input type="submit" value="Login" >
</form>
</body>
</html>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Welcome </title>
</head>
<body>
<h4>
Welcome
<%=session.getAttribute("name")%></h4>
</body>
</html>
package com.test.dao;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
public class LoginDao {
public static boolean validate(String name, String pass) {
boolean status = false;
Connection conn = null;
PreparedStatement pst = null;
ResultSet rs = null;
String url = "jdbc:mysql://localhost:3306/";
String dbName = "test";
String driver = "com.mysql.jdbc.Driver";
String userName = "root";
String password = "12345";
try {
Class.forName(driver).newInstance();
conn = DriverManager
.getConnection(url + dbName, userName, password);
pst = conn
.prepareStatement("select * from user where email=? and password=?");
pst.setString(1, name);
pst.setString(2, pass);
rs = pst.executeQuery();
status = rs.next();
} catch (Exception e) {
System.out.println(e);
} finally {
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (pst != null) {
try {
pst.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (rs != null) {
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
return status;
}
}
package com.test.servlets;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import com.amzi.dao.LoginDao;
public class LoginServlet extends HttpServlet{
private static final long serialVersionUID = 1L;
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
String n=request.getParameter("username");
String p=request.getParameter("userpass");
HttpSession session = request.getSession(false);
if(session!=null)
session.setAttribute("name", n);
if(LoginDao.validate(n, p)){
RequestDispatcher rd=request.getRequestDispatcher("welcome.jsp");
rd.forward(request,response);
}
else{
out.print("Invalid Credentials");
RequestDispatcher rd=request.getRequestDispatcher("index.jsp");
rd.include(request,response);
}
out.close();
}
}