如何用jsp页面生成随机的验证数字码

checkNum.jsp

<%@ page language="java" import="java.util.*,java.sql.*" pageEncoding="UTF-8"%>

<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,javax.imageio.*"%>

<%

String path = request.getContextPath();

String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";

%>

<%!

Color  getRandColor(int fc,int bc)//给定范围随机选颜色

{

Random random = new Random();

if(fc>255) fc= 255;

if(bc>255) bc= 255;

int r= fc+random.nextInt(bc-fc);

int g= fc+random.nextInt(bc-fc);

int b= fc+random.nextInt(bc-fc);

return new Color(r,g,b);

}

%>

<%

response.setHeader("Pragma","No-cache");//设置页面不缓冲

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

response.setDateHeader("Expires",0);

int width=60,height=20;

BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);

Graphics g = image.getGraphics();//获取图像上下文

Random random = new Random();//生成随机对象

g.setColor(getRandColor(200,250));

g.fillRect(0,0,width,height);

g.setFont(new Font("Times New Roman",Font.PLAIN,18));//设置字体

for(int i=0;i<155;i++)

{

int x=random.nextInt(width);

int y=random.nextInt(height);

int x1 = random.nextInt(12);

int y1 = random.nextInt(12);

g.drawLine(x,y,x+x1,y+y1);

}

//随机产生验证码

String sRand = "";

for(int i=0;i<4;i++)

{

String rand = String.valueOf(random.nextInt(10));

sRand+=rand;

//将验证码显示到图像中

g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));

//设置显示随机数的颜色

g.drawString(rand,13*i+6,16);

}

//将验证码存放到session中

session.setAttribute("rand",sRand);

//图像生效

g.dispose();

//输出图像到页面

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

out.clear();

out = pageContext.pushBody();

%>

可以在登录login.jsp下直接通过：   这种格式调用； 

                验证码:<input class="imgbutton"  name="checknum" type="text" size="15" id ="checknum" maxlength="4"/>

      <img src="checknum.jsp" alt="Change" border="1" οnclick="changeCheckNum()"/><br/>

      <input type="submit" name="submit" value="login"/>