[Java知识库]JavaWeb Servlet 生成简易图片验证码

Servlet 类

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;

/**
 * Servlet 生成一个简易的图片验证码，并3秒刷新一次
* */
public class ImageServlet extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //  让浏览器页面3秒自动刷新
        resp.setHeader("refresh","3");
        // 在内存创建一个图片
        BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_BGR);
        // 得到图片
        Graphics2D graphics2D = (Graphics2D)image.getGraphics(); // 相当于画笔
        // 设置图片的背景颜色
        graphics2D.setColor(Color.white);
        graphics2D.fillRect(0,0,80,20);
        // 给图片写数据
        graphics2D.setColor(Color.BLUE);
        graphics2D.setFont(new Font(null,Font.BOLD,20));
        graphics2D.drawString(getRandomNum(),0,20);
        // 告诉浏览器以图片的方式打开
        resp.setContentType("image/jpeg");
        // 网站存在缓存，不让网站缓存
        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());
    }

    @Override
    protected void doPut(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }

    // 生成随机数
    public String getRandomNum(){
        Random random = new Random();
        String num = random.nextInt(9999999) + "";

        StringBuilder stringBuffer = new StringBuilder();
        for (int i=0;i<7-num.length();i++){
            stringBuffer.append(0);
        }

        num = stringBuffer.toString()+num;
        return num;
    }
}

web.xml

<?xml version="1.0" encoding="UTF-8" ?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
                http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">

    <!--注册Servlet-->
   
    <servlet>
        <servlet-name>img</servlet-name>
        <servlet-class>com.test.servlet.ImageServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>img</servlet-name>
        <url-pattern>/img</url-pattern>
    </servlet-mapping>


</web-app>

生成效果（每三秒书刷新一次）：

?