JavaWeb 验证码

package com.gen;

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 imageController extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //设置浏览器三秒刷新一次
        resp.setHeader("refresh", "3");
        //在内存中创建一个图片
        BufferedImage bufferedImage = new BufferedImage(100, 30, BufferedImage.TYPE_INT_RGB);
        //获取图片
        Graphics2D graphics = (Graphics2D) bufferedImage.getGraphics();
        //设置背景颜色
        graphics.setColor(Color.white);
        //设置字体
        graphics.setFont(new Font(null,Font.BOLD,30));
        graphics.drawString(makenum(), 0, 30);
        //指定浏览器要打开的方式
        resp.setContentType("image/jpeg");
        //设置浏览器无缓存
        resp.setDateHeader("expires",-1);
        resp.setHeader("Cache-control","no-cache");
        resp.setHeader("Pragma","no-cache");
        //输出客户端
        ImageIO.write(bufferedImage,"jpg",resp.getOutputStream());
    }

    private String makenum() {
        int num = new Random().nextInt(9999);
        StringBuffer sb = new StringBuffer();
        for (int j = 0; j < 4.; j++) {
            sb.append("0");
        }
        return sb.toString() + num;
    }

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