jsp动态生成验证码的类

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.imageio.stream.ImageOutputStream;

public class RandomNumUtil {
    private ByteArrayInputStream image;//图像   
    private String str;//验证码   
       
    private RandomNumUtil(){   
        init();//初始化属性   
    }   
     
    public static RandomNumUtil Instance(){   
        return new RandomNumUtil();   
    }   
     
    public ByteArrayInputStream getImage(){   
        return this.image;   
    }   
     
    public String getString(){   
        return this.str;   
    }   
       
    private void init() {   
        //       在内存中创建图象   
        int width=85, 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));   
        //       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(6位数字)  
        String sRand="";
        for (int i=0;i<6;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);
        }
        //赋值验证码
        this.str=sRand; 
        
        //图象生效   
        g.dispose();   
        ByteArrayInputStream input=null;   
        ByteArrayOutputStream output = new ByteArrayOutputStream();   
        try{   
            ImageOutputStream imageOut = ImageIO.createImageOutputStream(output);   
            ImageIO.write(image, "JPEG", imageOut);   
            imageOut.close();   
            input = new ByteArrayInputStream(output.toByteArray());   
        }catch(Exception e){   
            System.out.println("验证码图片产生出现错误："+e.toString());   
        }   
           
        this.image=input; 
    }   
     
    private Color getRandColor(int fc,int bc){   
        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);   
   }
}