生成验证码图片

package com.test;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;   
import java.awt.image.BufferedImage;   
import java.io.IOException;   
import java.io.OutputStream;   
import java.util.Random;   
  
import javax.imageio.ImageIO;   
  
public class ImageNum {   
       
    //验证码图片中可以出现的字符集，可根据需要修改   
    private char mapTable[]={   
            'a','b','c','d','e','h',   
            'j','k','m','n','p','q',   
            'r','s','t','u','v','w',   
            'x','y','z','0','2','3',   
            '4','5','6','7','8','9'  
    };   
       
    public String getCertPic(int width, int height,OutputStream os) {   
        if(width<=0) {   
            width=60;   
        }   
        if(height<=0) {   
            height=20;   
        }   
           
        BufferedImage image = new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB);   
        //获取图形上下文   
        Graphics g = image.getGraphics();   
        //设定背景颜色   
        g.setColor(new Color(0xDCDCDC));   
        g.fillRect(0, 0, width, height);   
        //画边框   
        g.setColor(Color.black);   
        g.drawRect(0, 0, width-1, height-1);   
        //随机产生的验证码   
        String strEnsure="";   
        //4代表4位验证码，如果要生成等多位的验证码 ，则加大数值   
        
        for(int i=0; i<4; i++) {   
            strEnsure += mapTable[(int)(mapTable.length*Math.random())];
        }
        //将验证码显示在图像中，如果要生成更多位的验证码，增加drawString语句   
        g.setColor(Color.black);   
        g.setFont(new Font("Atlantic Inline", Font.PLAIN,18));   
        String str = strEnsure.substring(0, 1);   
        g.drawString(str, 8, 17);   
         str = strEnsure.substring(1, 2);   
         g.drawString(str, 20, 15);   
         str = strEnsure.substring(2, 3);   
         g.drawString(str, 35, 18);   
         str = strEnsure.substring(3, 4);   
         g.drawString(str, 45, 15);   
         //随机产生10个干扰点   
            
         Random random = new Random();   
         for(int i=0; i<10; i++ ) {   
             int x = random.nextInt(width);   
             int y = random.nextInt(height);   
             g.drawOval(x, y, 1, 1);   
         }
        //释放图形上下文   
         g.dispose();   
         try{   
             //输出图像到页面   
             ImageIO.write(image, "JPEG", os);
         }catch(IOException e) {   
             return "";   
         }   
        return strEnsure;   
    }   
}