Java Web之验证码

　　今天来模拟一下验证码，我们需要三个文件，两个Servlet，一个jsp

　　直接贴代码吧

RandomCodeServlet：主要负责生产验证码

package com.vae.RandomCode;

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;
import java.util.UUID;
@WebServlet("/randomcode")
public class RandomCodeServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //生成随机数
        String randomCode= UUID.randomUUID().toString().substring(0,5);
        //把随机数放进session，作为对比的凭证
        req.getSession().setAttribute("RANDOM_IN_SESSION",randomCode);

        //创建图片对象
        int width=80;
        int height=40;
        int imageType=BufferedImage.TYPE_INT_RGB;
        BufferedImage image=new BufferedImage(width,height,imageType);

        //画板
        Graphics g=image.getGraphics();
        g.setColor(Color.YELLOW);
        //绘制一个实心的矩形
        g.fillRect(1,1,width-2,height-2);

        //把随机数画进图片中
        g.setColor(Color.BLACK);
        Font font=new Font("宋体",Font.BOLD+Font.ITALIC,20);
        g.setFont(font);
        g.drawString(randomCode,10,20);
        //干扰线，这个的目的就是为了防止黑客去用软件识别验证码
        g.setColor(Color.GRAY);
        Random r=new Random();
        for (int i = 0; i < 100; i++) {
            g.fillRect(r.nextInt(width),r.nextInt(height),2,2);
        }

        //关闭
        g.dispose();
        //把图片对象以流的方式保存出去
        ImageIO.write(image,"jpg",resp.getOutputStream());



    }
}

LoginServlet：主要负责接收JSP传来的参数，验证码和用户输入的验证码进行一个对比

package com.vae.RandomCode;

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.io.IOException;
@WebServlet("/randomlogin")
public class LoginServlet extends HttpServlet {
    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //1.接收参数
        String name=req.getParameter("username");
        String email=req.getParameter("email");
        String randomcode=req.getParameter("randomcode");
        //2.获取session中的随机数，判断验证码是否正确
        String randomcodesession=req.getSession().getAttribute("RANDOM_IN_SESSION").toString();
        if (!randomcode.equalsIgnoreCase(randomcodesession)) {
            req.setAttribute("errogMsg","验证码不对，请重新输入");
            req.getRequestDispatcher("/randomcode/randomlogin.jsp").forward(req,resp);
            return;
        }
        System.out.println("验证码正确");
        req.getSession().removeAttribute("RANDOM_IN_SESSION"); //删除缓存

    }

}

最后一个是我们的JSP

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>验证码登录</title>
</head>
<body>
<h3>用户登录</h3>
${errogMsg}
<form action="/randomlogin" method="post">
    账号：<input type="text" name="username" id="username" required/><br>
    邮箱：<input type="email" name="email" id="email" required><br>
    验证码：<input type="text" name="randomcode" id="randomcode" size="5" maxlength="5">
    <img src="/randomcode" id="randomcodeImg" title="看不清，换一张"
          style="cursor: pointer;"  onclick="change()" >

    <input type="submit" value="注册">
</form>

<script type="text/javascript">
    function change() {
        //刷新验证码的图片
        document.getElementById("randomcodeImg").src="/randomcode?"+new Date().getTime();
    }
</script>

</body>
</html>

　　看看效果

就这么简单，但是有一个问题啊，就是表单重复提交了怎么办？我们不能表单重复提交，这个问题下篇文章专门来介绍一下

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