java中servlet实现登录验证的方法

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login.java:
代码如下：

package com.ncu;
import java.io.PrintWriter;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class login extends HttpServlet{
 public void doGet(HttpServletRequest req,HttpServletResponse res){
  try{
   //res.setCharacterEncoding("utf-8");
   res.setContentType("text/html;charset=gbk");
   PrintWriter pw=res.getWriter();
   //返回登录界面
   pw.print("html");
   pw.print("head");
   pw.print("title登录界面/title/head");
   pw.print("body");
   pw.print("h1用户登录界面/h1");
   pw.print("form action='loginpro' method=post");
   pw.print("用户名：input type=text name=userNamebr");
   pw.print("密码：input type=password name=Pwdbr");
   pw.print("input type=submit value=submit");
   pw.print("/body/html");

   
  }catch(Exception e)
  {
   e.printStackTrace();
  }
 }
}

LoginPro.java:
代码如下：

package com.ncu;
import java.io.PrintWriter;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginPro extends HttpServlet{
 public void doPost(HttpServletRequest req,HttpServletResponse res){
  try{
   String user=req.getParameter("userName");
   String pwd=req.getParameter("Pwd");
   if(user==null){
    user="";
   }
   if(pwd==null)
   {
    pwd="";
   }
   if(user.equals("nicolas")&&pwd.equals("nicolas")){
    //用户和密码合法
    //res.sendRedirect("wel");
//    res.setCharacterEncoding("gbk");
//    PrintWriter pw=res.getWriter();
//    pw.print("恭喜你，登录成功！！");
    res.sendRedirect("welcome");

   }
   else{
    //不合法进行跳转

    res.sendRedirect("login");//跳转到登录界面
   }

   
  }catch(Exception e)
  {
   e.printStackTrace();
  }
 }
}

Welcome.java:

代码如下：

package com.ncu;
import java.io.PrintWriter;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Welcome extends HttpServlet{
 public void doGet(HttpServletRequest req,HttpServletResponse res){
  try{
   res.setCharacterEncoding("gbk");
   PrintWriter pw=res.getWriter();
   pw.print("welcome，您好");

  }catch(Exception e)
  {
   e.printStackTrace();
  }
 }
}

web.xml
代码如下：

?xml version="1.0" encoding="UTF-8"?
web-app version="3.0"
 xmlns="http://java.sun.com/xml/ns/javaee"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
 http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
  display-name/display-name 
  welcome-file-list
    welcome-fileindex.jsp/welcome-file
  /welcome-file-list
  servlet
  !-- 给你的servlet取名，任意的 --
  servlet-namehello/servlet-name
  !-- 指明servlet的路径（包名+类名 --
  servlet-classcom.ncu.Hello/servlet-class

  /servlet
   servlet-mapping
   !-- 这个servlet名必须和映射的一致 --
     servlet-namehello/servlet-name

  !-- 这是在浏览器中输入的访问该servlet的url --
  url-pattern/nicolas/url-pattern
  /servlet-mapping
  servlet
  servlet-namehelloservlet/servlet-name
  servlet-classcom.ncu.HelloServlet/servlet-class
  /servlet
  servlet-mapping
  servlet-namehelloservlet/servlet-name
  url-pattern/helloservlet/url-pattern
  /servlet-mapping
  servlet
  servlet-namehelloHttpServlet/servlet-name
  servlet-classcom.ncu.helloHttpServlet/servlet-class
  /servlet
  servlet-mapping
  servlet-namehelloHttpServlet/servlet-name
  url-pattern/helloHttpServlet/url-pattern
  /servlet-mapping
  servlet
  servlet-namelogin/servlet-name
  servlet-classcom.ncu.login/servlet-class
  /servlet
  servlet-mapping
  servlet-namelogin/servlet-name
  url-pattern/login/url-pattern
  /servlet-mapping
  servlet
  servlet-nameloginpro/servlet-name
  servlet-classcom.ncu.LoginPro/servlet-class
  /servlet
  servlet-mapping
  servlet-nameloginpro/servlet-name
  url-pattern/loginpro/url-pattern
  /servlet-mapping
  servlet
  servlet-namewelcome/servlet-name
  servlet-classcom.ncu.Welcome/servlet-class
  /servlet
  servlet-mapping
  servlet-namewelcome/servlet-name
  url-pattern/welcome/url-pattern
  /servlet-mapping
/web-app