准备阶段
IDEA中需要调用request.getParameter，需要导入包，详情参考https://blog.csdn.net/Yuz_99/article/details/90107695
，解决爆红问题。
具体步骤
建立三个jsp文件，具体如下
login.jsp:
<%--
Created by IntelliJ IDEA.
User: 长风
Date: 2019/9/5
Time: 22:20
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" import="java.util.*" %>
<html>
<head>
<title>登陆页面</title>
</head>
<body>
<form action="logincheck.jsp">
<table>
<tr>
<td>输入用户名：</td>
<td><input type="text" name="name" value="<%=request.getParameter("name")%>" size="16"></td>
</tr>
<tr>
<td>输入密码：</td>
<td><input type="password" name="password" size="16"></td>
</tr>
<tr>
<td><input type="submit" value="登陆"></td>
</tr>
</table>
</form>
</body>
</html>
logincheck.jsp:
<%--
Created by IntelliJ IDEA.
User: 长风
Date: 2019/9/5
Time: 22:40
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>处理登陆页面</title>
</head>
<body>
<%
String name = request.getParameter("name");
String password = request.getParameter("password");
if (name.equals("QQ") && password.equals("123")) { //确定用户名为QQ,登陆密码为123
%>
<jsp:forward page="success.jsp">
<jsp:param name="user" value="<%=name%>"/>
</jsp:forward>
<%--如果登陆成功，传递用户名到success.jsp文件通过request.getParameter接收--%>
<%
} else {
%>
<jsp:forward page="login.jsp">
<jsp:param name="user" value="<%=name%>"/>
</jsp:forward>
<%--如果登陆失败，传递用户名到login.jsp文件，表格中显示上一次登陆用户名，而不再是null--%>
<%
}
%>
</body>
</html>
success.jsp:
<%--
Created by IntelliJ IDEA.
User: 长风
Date: 2019/9/5
Time: 22:50
To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>登陆成功页面</title>
</head>
<body>
登陆成功
<hr>
欢迎<%=request.getParameter("name")%>访问本网站！
</body>
</html>
运行结果
2.
3.
4.如果输入错误
