登录注册验证码编写以及动态验证

1、验证码工具类

        CheckCodeServlet

package com.rk.utils;

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 java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

/**
 * 验证码
 */
@WebServlet("/checkCodeServlet")
public class CheckCodeServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {
		
		//服务器通知浏览器不要缓存
		response.setHeader("pragma","no-cache");
		response.setHeader("cache-control","no-cache");
		response.setHeader("expires","0");
		
		//在内存中创建一个长80，宽30的图片，默认黑色背景
		//参数一：长
		//参数二：宽
		//参数三：颜色
		int width = 80;
		int height = 30;
		BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
		
		//获取画笔
		Graphics g = image.getGraphics();
		//设置画笔颜色为灰色
		g.setColor(Color.GRAY);
		//填充图片
		g.fillRect(0,0, width,height);
		
		//产生4个随机验证码，12Ey
		String checkCode = getCheckCode();
		//将验证码放入HttpSession中
		request.getSession().setAttribute("CHECKCODE_SERVER",checkCode);
		
		//设置画笔颜色为黄色
		g.setColor(Color.YELLOW);
		//设置字体的小大
		g.setFont(new Font("黑体",Font.BOLD,24));
		//向图片上写入验证码
		g.drawString(checkCode,15,25);
		
		//将内存中的图片输出到浏览器
		//参数一：图片对象
		//参数二：图片的格式，如PNG,JPG,GIF
		//参数三：图片输出到哪里去
		ImageIO.write(image,"PNG",response.getOutputStream());
	}
	/**
	 * 产生4位随机字符串 
	 */
	private String getCheckCode() {
		String base = "0123456789ABCDEFGabcdefg";
		int size = base.length();
		Random r = new Random();
		StringBuffer sb = new StringBuffer();
		for(int i=1;i<=4;i++){
			//产生0到size-1的随机值
			int index = r.nextInt(size);
			//在base字符串中获取下标为index的字符
			char c = base.charAt(index);
			//将c放入到StringBuffer中去
			sb.append(c);
		}
		return sb.toString();
	}
	public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		this.doGet(request,response);
	}
}

2、login.jsp页面显示验证码

         <div class="form-inline">
            <label  class="col-sm-2 control-label">Check</label>
            <input type="text" name="verifycode" class="form-control col-sm-6" id="verifycode" placeholder="Please Check" style="width: 120px;"/>
            <a href="javascript:refreshCode()" onclick="refreshCode()" class="col-sm-4">
                <img src="${pageContext.request.contextPath}/checkCodeServlet" title="看不清点击刷新" id="vcode"/>
            </a>
        </div>

3、使用js让其切换

<script>
    //切换验证码
    function refreshCode() {
        //1、获取验证码图片对象
        var vcode = document.getElementById("vcode");
        //2、设置其src属性，加时间戳
        vcode.src="${pageContext.request.contextPath}/checkCodeServlet?time="+new Date().getTime();
    }
</script>

4、后台校验验证码

 String verifycode1 = request.getParameter("verifycode");//用户输入的验证码
        String checkcode_server = (String) request.getSession().getAttribute("CHECKCODE_SERVER");//生成的验证码
        if(verifycode1.equals("")||!checkcode_server.equalsIgnoreCase(verifycode1))//不输入verifycode为空字符串，不是null
        {
            model.addAttribute("msg","验证码错误");
            request.getSession().removeAttribute("CHECKCODE_SERVER");//使用过后要移除
            return "login";//返回到登录页面
        }

结果: