动态验证码 关键代码

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;
/**
 * 动态验证码 关键代码
 * @author xiaer
 *
 */
public class ImageEnsure {
	public ImageEnsure() {
	}
	
	private char mapTable[]={
			  'A','B','C','D','E','F',
			  'G','H','I','J','K','L',
			  'M','N','P','Q','R',
			  'S','T','U','V','W','X',
			  'Y','Z','0','1','2','3',
			  '4','5','6','7','8','9'};


	public String getEnsure(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(); 

		  // 设定背景色 
		  g.setColor(new Color(0xFCF000)); 
		  g.fillRect(0, 0, width, height); 

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

		  // 取随机产生的认证码
		  String strEnsure = "";

		  // 4代表4位验证码
		  for(int i=0; i<4; ++i) {
		   strEnsure += mapTable[(int)(mapTable.length*Math.random())];
		  }
		  
		  // 将认证码显示到图象中 
		  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50个干扰点
		  Random rand = new Random();
		  for (int i=0;i<50;i++) 
		  { 
		   int x = rand.nextInt(width); 
		   int y = rand.nextInt(height); 
		   g.drawOval(x,y,1,1); 
		  } 



		// 释放图形上下文
		g.dispose(); 
		
		try {
			// 输出图象到页面 
			ImageIO.write(image, "JPEG", os);
		} catch (IOException e) {
			return "";
		}finally{
			
		}
		
		return strEnsure;
	}
/*	
	public static void main(String []args) {
		try{
			BufferedOutputStream os = new BufferedOutputStream(
											new FileOutputStream("c:\\test.jpg"));
	       new ImageEnsure().getEnsure(100, 200, os);
			os.flush();
			os.close();
		} catch(Exception e) {}
	}
*/
}