写好的验证界面(四位数数据随机组合)

<%@ page contentType="image/jpeg" 
pageEncoding="GBK"
import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %> 
<%! 
Color getRandColor(int fc,int bc){//给定范围获得随机颜色 
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); 
} 
%> 
<% 
//设置页面不缓存 
//System.setProperty("java.awt.headless","true");
out.clear();
response.setHeader("Pragma","No-cache"); 
response.setHeader("Cache-Control","no-cache"); 
response.setDateHeader("Expires", 0); 

// 在内存中创建图象 
int width=60, height=20; 
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); 

// 获取图形上下文 
Graphics g = image.getGraphics(); 

//生成随机类 
Random random = new Random(); 

// 设定背景色 
g.setColor(getRandColor(200,250)); 
g.fillRect(0, 0, width, height); 

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

//画边框 
//g.setColor(new Color()); 
//g.drawRect(0,0,width-1,height-1); 


// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到 
g.setColor(getRandColor(160,200)); 
for (int i=0;i<155;i++) 
{ 
int x = random.nextInt(width); 
int y = random.nextInt(height); 
int xl = random.nextInt(12); 
int yl = random.nextInt(12); 
g.drawLine(x,y,x+xl,y+yl); 
} 

// 取随机产生的认证码(4位数字) 
String sRand=""; 
for (int i=0;i<4;i++){ 
String rand=String.valueOf(random.nextInt(10)); 
sRand+=rand; 
// 将认证码显示到图象中 
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));//调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成 
g.drawString(rand,13*i+6,16); 
} 

// 将认证码存入SESSION 
request.getSession().setAttribute("rand",sRand); 
System.out.println(sRand);


// 图象生效 
g.dispose(); 

// 输出图象到页面 
ImageIO.write(image, "JPEG", response.getOutputStream()); 
out.clear();
out = pageContext.pushBody();

%>