Response生成验证码

类代码：

package com.yin;


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 Image extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //浏览器3秒刷新1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,一只2D的画笔
        Graphics2D g=(Graphics2D)image.getGraphics();
        //设置图片的背景颜色
        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.setHeader("Cache-Control","no-cache");
        resp.setHeader("Pragma","no-cache");
        //吧图片写给浏览器
        ImageIO.write(image,"jpg",resp.getOutputStream());
    }

    private String makeNum(){
        Random random=new Random();
        String num=random.nextInt(999999)+"";
        StringBuffer sb=new 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.doGet(req, resp);
    }
}

　　web.xml中插入

    <servlet>
        <servlet-name>image</servlet-name>
        <servlet-class>com.yin.Image</servlet-class>
    </servlet>
    <servlet-mapping>
        <servlet-name>image</servlet-name>
        <url-pattern>/img</url-pattern>
    </servlet-mapping>

　　显示结果；