jsp实例：一个简单的用户登陆系统

三个文件如下：

//登录界面

/** *//**

* @(#)Login.Java

*

*

* @author shiyi05

* @version 1.00 2008/5/10

*/

package com.rao;

import javax.Servlet.http.*;

import java.io.*;

public class Login extends HttpServlet

{

public Login()

{

}

//处理Get请求

public void doGet(HttpServletRequest req,HttpServletResponse res) {

try

{

//中文乱码

res.setContentType("text/html; charset=gbk");

PrintWriter pw=res.getWriter();

//返回登陆界面

pw.println("");

pw.println("");

pw.println("

登陆界面

");

pw.println("

");

pw.println("用户名:
"); pw.println("密码：
"); pw.println("
");

pw.println("");

pw.println("");

}

catch(Exception ex)

{

ex.printStackTrace();

}

}

public void doPost(HttpServletRequest req,HttpServletResponse res) {

this.doGet(req,res);

}

}

//用户验证

/** *//**

* @(#)LoginCl.java

*

* @author shiyi05

* @version 1.00 2008/5/10

*/

package com.rao;

import javax.servlet.http.*;

import java.io.*;

public class LoginCl extends HttpServlet

{

public LoginCl()

{

}

//处理Get请求

public void doGet(HttpServletRequest req,HttpServletResponse res) {

try

{

//中文乱码

res.setContentType("text/html; charset=gbk");

//接收用户名和密码

String u=req.getParameter("username");

String p=req.getParameter("passwd");

//验证

if(u.equals("sp") && p.equals("123"))

//合法

res.sendRedirect("Welcome");

}

else

{

//不合法

res.sendRedirect("Login");

}

}

catch(Exception ex)

{

ex.printStackTrace();

}

}

public void doPost(HttpServletRequest req,HttpServletResponse res) {

this.doGet(req,res);

}

}

//欢迎界面

/** *//** *//** *//**

* @(#)Welcome.java

*

*

* @author shiyi05

* @version 1.00 2008/5/10

*/

package com.rao;

import javax.servlet.http.*;

import java.io.*;

public class Welcom e extends HttpServlet

{

public Welcome()

{

}

//处理Get请求

public void doGet(HttpServletRequest req,HttpServletResponse res) {

try

{

//中文乱码

res.setContentType("text/html; charset=gbk");

PrintWriter pw=res.getWriter();

//返回登陆界面

pw.println("");

pw.println("");

pw.println("

Welcome

");

pw.println("");

pw.println("");