javaWeb通过验证码的使用实现简单登录

简单的流程图

1.用户给第一次访问login.jsp页面时，会想服务器发送两个请求，一个请求是显示图片，还有一个是显示表单

2.第一个请求发送后服务器中verifyServlet处理，随机生成验证码图片，并保存到session中，然后响应给客户端

3.第二个请求后服务器LoginServlet处理，获取表单验证码，以及session中的验证码，再判断两个验证码是否相等，相等就向下执行即 success.jsp，否则跳转到login.jsp页面

1.创建login.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'login.jsp' starting page</title>
    
	<meta http-equiv="pragma" content="no-cache">
	<meta http-equiv="cache-control" content="no-cache">
	<meta http-equiv="expires" content="0">    
	<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
	<meta http-equiv="description" content="This is my page">
	<!--
	<link rel="stylesheet" type="text/css" href="styles.css">
	-->

  </head>
  
  <body>
    <%--本页面提供登录表单,还有显示错误信息 --%>
   <h1>登录</h1> 
   <%
   	//读取uname的cookie
   	String uname="";
   	Cookie[] cs=request.getCookies();
   	if(cs!=null){
   		for(Cookie c:cs){
   			if("uname".equals(c.getName())){
   				uname=c.getValue();
   			}
   		}
   	}
    %>
   
   <%
    String message="";
   	String msg=(String)request.getAttribute("msg");
   	if(msg!=null){
   	 	message=msg;
   	 }
    %>
   
   <font color="red"><b><%=message %></b></font>
   <form action="/ServletDemo2/LoginServlet1" method="post">
     用户名：<input type="text" name="username" value=<%=uname %> /><br>
      密  码：<input type="password"  name="pawword" /><br>
      验证码:<input type="text" name="verifycode" size="3">
       <img src="/ServletDemo2/VerifyServlet" >
     <!--  <a href="javascript:_change()">换一张</a> -->
  
      <input type="submit" value="登录" />
   
   </form>
  </body>
</html>

2.success.jsp(只是简单的展示)

<body>
    <h1>succ1</h1>
    <%
    String username=(String)session.getAttribute("username");
    if(username==null){
    	/*
    	向request域中保存错误信息，转发到login.jsp
    	*/
    	request.setAttribute("msg", "请先登录再访问");
    	request.getRequestDispatcher("/session2/login.jsp").forward(request, response);
    	return;
    }
     %>
    
    欢迎登陆成功<%=username %>
  </body>

3.然后是VerifyServlet

package com.klay.servlet.session;

import java.awt.image.BufferedImage;
import java.io.IOException;

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 com.klay.image.VerifyCode;

/**
 * Servlet implementation class VerifyServlet
 */
@WebServlet("/VerifyServlet")
public class VerfiyServlet extends HttpServlet
{
	private static final long serialVersionUID = 1L;

	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        VerifyCode vc = new VerifyCode();
        BufferedImage image = vc.getImage();
        request.getSession().setAttribute("session_vcode", vc.getText());// 保存图片上的文本到session

        VerifyCode.output(image, response.getOutputStream());
	}

}

4.LoginServlet

package com.klay.servlet.session;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class LoginServlet extends HttpServlet
{

    /**
     * @Fields serialVersionUID : TODO(用一句话描述这个变量表示什么)
     */
    private static final long serialVersionUID = 1L;

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp)
            throws ServletException, IOException
    {
        /**
         * 获取校验码
         */
        String sessionCode = (String) req.getSession()
                .getAttribute("session_vcode");

        String paraCode = req.getParameter("verifycode");

        if (!paraCode.equalsIgnoreCase(sessionCode))
        {
            req.setAttribute("msg", "验证码错误");
            req.getRequestDispatcher("/session2/login.jsp").forward(req, resp);
            // return是这里执行完，就不玩下执行了。
            return;
        }

        /**
         * 获取表单信息
         */
        req.setCharacterEncoding("utf-8");

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

        /**
         * 校验用户名和密码
         */
        if (!"kevin".equalsIgnoreCase(username))// 成功
        {
            Cookie cookie = new Cookie("uname", username);
            resp.addCookie(cookie);

            /*
             * 成功就保存用户信息到session，并重定向succ1.jsp
             */
            HttpSession session = req.getSession();
            session.setAttribute("username", username);
            resp.sendRedirect("/ServletDemo2/session2/succ1.jsp");
        }
        else
        {// 失败
         // 如果失败，保存错误信息到requset，转发到login.jsp
         // (服务器内部跳转只有一个request请求，重定向会有新的request，就不能获取错误信息)
            req.setAttribute("msg", "用户名或密码错误");
            RequestDispatcher rd = req
                    .getRequestDispatcher("/session2/login.jsp");
            rd.forward(req, resp);// 转发

        }

    }

}

原文链接：https://blog.csdn.net/clay996/article/details/80845301

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