后端实现：需要用到java的图片类，生产一个图片?
public class ImageServlet extends HttpServlet
{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException
{
//如何让浏览器每3秒刷新一次
resp.setHeader("Refresh","3");
//在内存中创建一个图片
BufferedImage image = new BufferedImage(80, 25, BufferedImage.TYPE_INT_RGB);
//得到图片
Graphics2D g =(Graphics2D) image.getGraphics();
//设置图片的背景颜色
g.setColor(Color.white);
g.fillRect(0,0,80,40);
//给图片写数据
g.setColor(Color.BLUE);//第一次设置白色的背景，第二次写数据使用蓝色
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，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());
}
//生成随机数
public String makeNum(){
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");
}
num = sb.toString()+num;
return num;
}
}<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
version="3.0"
metadata-complete="true">
<servlet>
<servlet-name>image</servlet-name>
<servlet-class>com.yinbo.servlet.ImageServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>image</servlet-name>
<url-pattern>/image</url-pattern>
</servlet-mapping>
</web-app>
