Response——验证码功能的实现

验证码怎么来的？

• 前端实现
• 后端实现，需要用到Java的图片类，生成一个图片

package com.kuang.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
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;

public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //如何让浏览器5秒自动刷新一次
        resp.setHeader("refresh","3");

        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);

        //得到图片
        Graphics2D g = (Graphics2D)image.getGraphics();  //相当于一支笔

        //设置图片的背景颜色
        g.setColor(Color.white);
        //填充背景色
        g.fillRect(0,0,80,20);

        //给图片写数据
        g.setColor(Color.blue);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(makeNum(),0,20);

        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/jpeg");

        //网站存在缓存，我们不能让浏览器缓存
        resp.setDateHeader("exprise",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");


        //把图片写给浏览器
        boolean write = ImageIO.write(image, "jpg",resp.getOutputStream());

    }

    //生成随机数
        private  String makeNum(){
            Random random = new Random();
            String num = random.nextInt(9999999)+ "";
            StringBuffer sb = new StringBuffer();
            //保证是7位数，如果不是，就追加0
            for(int i=0;i<7-num.length();i++){
                sb.append("0");
            }
            String s = sb.toString()+num;
            return  num;
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        super.doPost(req, resp);
    }
}

• web.xml

 
        ImageServlet
        com.kuang.servlet.ImageServlet
    
    
        ImageServlet
        /img