功能展示
功能：
1.一个登陆页面，当用户输入账号密码后(该账号密码为已给条件，定死了的值)，如果用户登陆正确则提示该用户登陆成功。
2.如果账号/密码错误，则在此次回到登录页面，且在登陆页面提示账号/密码错误。
3.如果用户直接访问登陆成功页面则提示:还未登录，并引导用户登录。
4.用户登录成功后需要显示:”‘用户的账号名’欢迎您”,且在后面添加退出登录按钮。
5.当用户点击退出登录按钮后需将用户退出。Admin
提示:注解都在代码中，如有错误或不了解请评论或联系博主.
代码展示
index.jsp
<%--
Created by IntelliJ IDEA.
User: Administrator
Date: 2021/4/1
Time: 11:19
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>用户登录页</title>
</head>
<body>
<form action="/LoginServlet" method="post">
用户名：<input type="text" name="username"/><br>
密码：<input type="password" name="password"/><br>
<input type="submit" value="登录">
<br>
<hr />
<%
//获取LoginServlet中32行error的值并赋值给变量"a".
String a=(String) session.getAttribute("error");
//实现消除主页面一直提示为"null"情况:
//判断变量"a"返回值是否为空[如果为空则证明登陆成功，不为空则登陆失败].
if (a!=null){ //如果不为空
out.print(a); //输出变量"a"的值.
}
else{ //反之输出"",[即为空，什么都没有]
out.print("");
}
%>
</form>
</body>
</html>
Welcome.jsp
<%--
Created by IntelliJ IDEA.
User: Administrator
Date: 2021/4/1
Time: 11:24
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Welcome</title>
</head>
<body>
<%
HttpSession session1=request.getSession();
String username=(String) session1.getAttribute("username");
if (username!=null){
out.print(username+"欢迎您！<a href='/LogOutServlet'>退出登录</a>");
}else{
out.print("您还未登录！请返回<a href=http://localhost:8080>登录</a>");
}
%>
</body>
</html>
LoginServlet
package Servlet;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");//设置编码格式，否则输出为乱码或"???"
PrintWriter out=response.getWriter();
request.setCharacterEncoding("utf-8");
// -----分割线-----
//获取的值为<index.jsp>页面中提交的值的信息：
//获取username的值并赋值给变量"username".
String username=request.getParameter("username");
//获取password的值并赋值给变量"password".
String password=request.getParameter("password");
// -----分割线-----
//判断获取到的"username"和"password"是否等于"admin"和"123".
if (username.equals("admin")&&password.equals("123")){
//声明调用方法
HttpSession session=request.getSession();
// -----分割线-----
//以username命名将username的值存入session域中.
session.setAttribute("username",username);
//重定向至"Welcome.jsp"页面
response.sendRedirect("/Welcome.jsp");
}
else { //反之
HttpSession session=request.getSession();
//存入session域信息
session.setAttribute("error","账号或密码错误，请重新输入！(っ °Д °;)っ [该提示3秒后刷新消失]");
//重写Cookie重新设置JSESSIONID的声明周期：
//新建Cookie命名为"JSESSIONID"值为获取到的session的ID，并赋值给变量"a".
Cookie c=new Cookie("JSESSIONID", session.getId());
c.setPath(request.getContextPath());
c.setMaxAge(3);//生存时间，以秒为单位.
response.addCookie(c);//将变量"c"添加到浏览器请求头
response.sendRedirect("http://localhost:8080");//重定向至URL:"http://localhost:8080"
}
// if (username!=null){
// out.print(username+"欢迎您！<a href='/LogOutServlet'>退出登录</a>");
// }else{
// out.print("您还未登录！请返回<a href=http://localhost:8080/index.jsp>登录</a>");
// }
}
}
LogOutServlet
package Servlet;
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 java.io.IOException;
import java.io.PrintWriter;
@WebServlet("/LogOutServlet")
public class LogOutServlet extends HttpServlet {
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/html;charset=utf-8");//设置编码格式，否则输出为乱码或"???"
PrintWriter out=response.getWriter();
request.setCharacterEncoding("utf-8");
// -----分割线-----
HttpSession session=request.getSession();
session.removeAttribute("username");//删除session域中存入的数据
out.print("退出成功，即将返回登录页面！");
response.setHeader("Refresh","3;URL=http://localhost:8080");
}
}
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