验证码

强制刷新 :除了禁止缓存以为，还需要给服务端传递一个唯一的参数值（没有实际用处）。随机数、时间

生成代码

<%@ page import="java.awt.*" %>
<%@ page import="java.util.Random" %>
<%@ page import="java.awt.image.BufferedImage" %>
<%@ page import="javax.imageio.ImageIO" %>
<%@ page contentType="image/jpeg;charset=UTF-8" language="java" %>
<%!
        //随机产生颜色值
        public Color getColor(){
            Random ran=new Random();
            int r = ran.nextInt(256);
            int g = ran.nextInt(256);
            int p = ran.nextInt(256);
            return new Color(r,g,p);//red green blue三原色0-255
        }
        //产生验证码值
        public  String getNum(){
            //0-8999    1000-9999
            int ran=(int)(Math.random()*9000)+1000;
            return String.valueOf(ran);
        }
%>
<%

    //禁止缓存，防止 验证码过期
    response.setHeader("Pragma","no-cache");
    response.setHeader("Cache-control","no-cache");
    response.setHeader("Expires","0");


    //绘制验证码
    BufferedImage image=new BufferedImage(80,30,BufferedImage.TYPE_INT_RGB);
    //画笔
    Graphics graphics = image.getGraphics();
    graphics.fillRect(0,0,80,30);
    //绘制干扰线条
    for(int i=0;i<60;i++){
        Random random=new Random();
     int xBegin  = random.nextInt(80);
     int yBegin  = random.nextInt(30);

     int xEnd= random.nextInt(xBegin+10);
     int yEnd= random.nextInt(yBegin+10);

     graphics.setColor(getColor());
     //绘制线条
     graphics.drawLine(xBegin,yBegin,xEnd,yEnd);
    }
    graphics.setFont(new Font("seif",Font.BOLD,20));
    //绘制验证码
    graphics.setColor(Color.BLACK);
    String checkCode=getNum();
    StringBuffer sb=new StringBuffer();
    for(int i=0;i<checkCode.length();i++){
        sb.append(checkCode.charAt(i));//验证码的每一位数字
    }
    graphics.drawString(sb.toString(),15,20);//绘制验证码

    //将验证码真实值保存zaisession中
    session.setAttribute("checkCode",checkCode);

    //真实的产生图片
    ImageIO.write(image,"jpeg",response.getOutputStream());

    //关闭
    out.clear();
    out=pageContext.pushBody();//<input type="image" src="xxx">
%>