全部代码：
package com.ftzlovedsj.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;
/**
* @author ${范涛之}
* @Description
* @create 2021-10-05 21:57
*/
public class ImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//如何让浏览器五秒刷新一次
resp.setHeader("refresh","3");
//在内存中创建一个图片
BufferedImage bufferedImage = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
//得到图片
Graphics2D g = (Graphics2D) bufferedImage.getGraphics();
//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);
//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","np-cache");
resp.setHeader("Pragma","no-cache");
//把图片写给浏览器
boolean write = ImageIO.write(bufferedImage,"jpg", resp.getOutputStream());
}
//生成随机数
private String makeNum(){
Random random = new Random();
String num = random.nextInt(9999999) + "";
StringBuffer sb = new StringBuffer(); //StringBuffer
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路由
<servlet>
<servlet-name>image</servlet-name>
<servlet-class>com.ftzlovedsj.servlet.ImageServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>image</servlet-name>
<url-pattern>/image</url-pattern>
</servlet-mapping>
效果图：
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