验证码原理和实现

Posted 2021-11-24 bakelFF

1、验证码的作用

验证码是目前大多网站所支持并使用于注册登录的。就在于其作用能有效防止暴力攻击、恶意登录注册，验证码每次都不同,

这就可以排除,用其他病毒或者软件自动申请用户及自动登陆.有效防止这种问题。

 

 

2、原理及知识点分析 

 1.原理

    验证码于服务器端生成，发送给客户端，并以图像格式显示。客户端提交所显示的验证码，客户端接收并进行比较，若比对失败则不能实现登录或注册，反之成功后跳转相应界面。

    2.主要知识

    服务器端的相关实现，前端运用 html 5，CSS 3 ,(可空白留给美工实现，须有  HTML  基础知识)。

    主要是三部分:

                           (提交界面， 成功及失败的)  jsp  

                           (后台对应提交  jsp  验证提交内容的) servlet  (生成验证码的) servlet

                           XML  文档

3、验证码实现 

前台代码：

<a style="cursor: hand" onclick="reload()">
<img alt="加载中..." src="${pageContext.request.contextPath }/CheckCodeServlet" id="img" border="1">
</a>

 

<script type="text/javascript">
		function reload(){
			document.getElementById("img").src
             = document.getElementById("img").src+"?aa="+new Date().getTime();//nocache
		}
</script>

java代码：

package com.school.controller;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.util.Random;
import javax.imageio.ImageIO;
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 javafx.scene.text.Font;

/**
 *验证码
 */
@WebServlet("/CheckCodeServlet")
public class CheckCodeServlet extends HttpServlet {
	
	protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		//设置缓存
		response.setHeader("pragma", "No-cache");
		response.setHeader("Cache-Control", "No-cache");
		response.setDateHeader("Expires", 0);
		//设置返回数据的类型
		response.setContentType("image/gif");
		//设置画板大小
		int width = 100;
		int height = 40;
		BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
		//画笔
		Graphics g = image.getGraphics();
		java.awt.Font font = new java.awt.Font("宋体",java.awt.Font.BOLD,25);
		g.setFont(font);
		String imagePath = request.getServletContext().getRealPath("/img/codeBackg.jpg");
		Image image1 = ImageIO.read(new File(imagePath));
		g.drawImage(image1,0,0,100,40,null);
		String source = "0123456789abcdefghijklmABCDEFGH好人坏人";
		String infor  = "";
		for (int i = 0; i < 4; i++) {
	        //随机取一个字符
			int index =  new Random().nextInt(source.length()-1);
			char myCode = source.charAt(index);
			//让字的颜色随机
			Random random = new Random();
			g.setColor(new Color(20+random.nextInt(120),20+random.nextInt(120),20+random.nextInt(120)));
			//画入文字
			g.drawString(myCode+"", 15+i*20, 20+new Random().nextInt(10));
			//画入干扰线
			g.drawLine(random.nextInt(100), random.nextInt(40), random.nextInt(100), random.nextInt(40));
			infor += myCode;
		}
		//记录到session，以备将来匹配
		request.getSession().setAttribute("infor", infor);
		//释放资源
		g.dispose();
		OutputStream out  = response.getOutputStream();
		ImageIO.write(image,"gif", out);
		out.flush();
		out.close();	
	}

	/**
	 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
	 */
	protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
		doGet(request, response);
	}

}

//接收输入的验证码
String code = request.getParameter("code");
//接收java生成的验证码
String infor = (String) request.getSession().getAttribute("infor");

//用equalsIgoreCase()方法判断是否相等，不区分大小写
if(!code.equalsIgnoreCase(infor)){
	//不正确
	loginError.put("code", "验证码不正确");
}