package com.cx;

//生成随机数的图片

import java.awt.Color;

import java.awt.Font;

import java.awt.Graphics;

import java.awt.image.BufferedImage;

import java.io.IOException;

import java.io.PrintWriter;

import java.util.Random;

import javax.imageio.ImageIO;

import javax.servlet.ServletException;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

public class CreateCode extends HttpServlet {

    public void doGet(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        //7.禁止浏览器缓存随机图片

        response.setDateHeader("Expires", -1);

        response.setHeader("Cache-Control", "no-cache");

        response.setHeader("Pragma", "no-cache");

        //6.通知客户机以图片方式打开发送过去的数据

        response.setHeader("Content-Type", "image/jpeg");

        //1.在内存中创建一副图片

        BufferedImage image=new BufferedImage(80, 30, BufferedImage.TYPE_INT_RGB);

        //2.在图片上写数据

        Graphics g=image.getGraphics();

        //设背景色

        g.setColor(Color.WHITE);

        g.fillRect(0, 0, 80, 30);

        //3.设置写入数据的颜色和字体

        g.setColor(Color.BLACK);

        g.setFont(new Font(null,Font.BOLD, 20));

        //4.向图片上写数据

        String num=makeNum();

        //将随机生成的数值保存到session

        request.getSession().setAttribute("checkcode", num);

        g.drawString(num, 0, 20);

        //5.把写好的数据的图片输出给浏览器

        ImageIO.write(image, "jpg", response.getOutputStream());

    }

    //该函数生成随机7位数

    public String makeNum(){

        Random r=new Random();

        //这里9999999可以生成7位

        String num=r.nextInt(9999)+"";

        StringBuffer sb=new StringBuffer();

        //如果不够4位，前面不补零

        for(int i=0;i<4-num.length();i++){

            sb.append("0");

        }

        num=sb.toString()+num;

        return num;

    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)

            throws ServletException, IOException {

        this.doGet(request, response);

    }

}

//使用

//<img src="/验证码的url"/>