jsp+servlet实现的验证登陆

可以将业务逻辑处理和视图相分离，使用jsp界面表示视图，使用servlet处理业务逻辑

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<%
String msg=(String)request.getAttribute("msg");
if(msg!=null){
out.print(msg);
}
%>
<form action="dologin" method="post">
username:<input type="text" name="username" /><br>
password:<input type="password" name="password" /><br>
<input type="submit" value="submit" />
</form>
</body>
</html>

success.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
登陆成功 
<%
String username=request.getParameter("username");
out.print(username+"欢迎你");
 %>
</body>
</html>

fail.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
登陆成功 
<%
String username=request.getParameter("username");
out.print(username+"欢迎你");
 %>
</body>
</html>

业务逻辑处理

com.zk.myservlet.dologin.java

public class dologin extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
    //获取表单数据
    String username=request.getParameter("username");
    String password=request.getParameter("password");
    //处理业务逻辑
    if("Tom".equals(username)&&"123".equals(password))
    {
    //分发转向
    request.getSession().setAttribute("username", username);
    request.getRequestDispatcher("/success.jsp").forward(request, response);
    //response.sendRedirect(request.getContextPath()+"/success.jsp");//丢失 username参数值 ，一次请求
    }
    else
    {
    //分发转向
    //request.getRequestDispatcher("/fail.jsp").forward(request,response);
    //response.sendRedirect(request.getContextPath()+"/fail.jsp");
          request.setAttribute("msg", "用户名密码不正确");
      request.getRequestDispatcher("/login.jsp").forward(request,response);
    }
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request,response);
    }
 
}