Response生成验证码

类代码：

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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

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<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；