package com.mahe666.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 VerificationCode extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //如何让浏览器每5秒自动刷新一次
        resp.setHeader("refresh","2");

        //在内存中创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
        //得到图片，graphics相当于在图片上画画的笔
        Graphics2D g = (Graphics2D) image.getGraphics();
        //设置图片的背景颜色
        g.setColor(Color.white);
        //填充白色
        g.fillRect(0,0,80,20);
        //给图片写数据
            //设置画笔颜色
        g.setColor(Color.BLUE);
        g.setFont(new Font(null,Font.BOLD,20));
        g.drawString(randomNum(),0,20);

        //告诉浏览器，这个请求用图片的方式打开
        resp.setContentType("image/jpg");
        //网站存在缓存，不让浏览器缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");

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

    }
    //生成6位随机数
    public String randomNum(){
        Random random = new Random();
        //nextInt里面的参数代表几位数和上限
        String num = random.nextInt(999999)+"";
        StringBuffer sb = new StringBuffer();
        for (int i = 0;i < 6-num.length(); i++){
            //不足六位的用0补
            sb.append("0");
        }
        return sb.toString() + num;

    }


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