java实现验证码三秒刷新

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java实现验证码三秒刷新

作为Java后端人掌握原理就行。

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 {@Overrideprotected 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");//在内存中创建图片//宽高三颜色BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_3BYTE_BGR);//在内存中得到图片Graphics2D g= (Graphics2D) image.getGraphics();//生成一个笔//设置图片背景颜色g.setColor(Color.white);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);//进行画画//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    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boolean write = ImageIO.write(image,"jpg", resp.getOutputStream());}public String makeNum(){//生成随机数/*** 保证必须是7位  如果 i < 7-num.length()要是成负数就会保存* 然后不够的直接用0填充*/Random random = new Random();String num = random.nextInt(9999999) + "";StringBuffer sb = new StringBuffer();for (int i = 0; i < 7-num.length(); i++) {sb.append("0");}String s = sb.toString() + num;return num;}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doGet(req, resp);}
}