<%@ page language="java"  pageEncoding="gb2312"%>
<%@ page contentType="image/jpeg" %>
<%@ page import="java.awt.*,java.awt.image.*" %>
<%@ page import="java.util.*,javax.imageio.*" %>

<%!
//產生隨機顏色函數
	Color getRandColor(int fc,int bc){
		Random r=new Random();
		if(fc>255) fc=255;
		if(bc>255) bc=255;
		int red=fc+r.nextInt(bc-fc);
		int green=fc+r.nextInt(bc-fc);
		int blue=fc+r.nextInt(bc-fc);
		return new Color(red,green,blue);
	}
 %>
 <%
 //設置頁面不緩存
 	response.setHeader("Pragma","NO-cache");
 	response.setHeader("Cache-Control","no-cache");
 	response.setDateHeader("Expires",0);
 	
 //創建隨機類
 	Random r=new Random();
 	
 //在內存中創建圖像，寬度為width,高度為height
 	int width=90,height=20;
 	BufferedImage pic=new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);
 
 //獲取圖形上下文環境
 	Graphics gc=pic.getGraphics();
 
 //設定背景色并進行填充
 	gc.setColor(getRandColor(200,250));
 	gc.fillRect(0,0,width,height);
 	
 //設定圖形上下文環境字體
 	gc.setFont(new Font("Times New Roman",Font.PLAIN,18));
 	
 //隨機產生200條干擾直線，使圖像中的認證碼不易被其他分析程序探測到
 	gc.setColor(getRandColor(160,200));
 	for(int i=0;i<200;i++){
 		int x1=r.nextInt(width);
 		int y1=r.nextInt(height);
 		int x2=r.nextInt(15);
 		int y2=r.nextInt(15);
 		gc.drawLine(x1,y1,x2,y2);
 		
 	}
 //隨機產生100個干擾點
 	gc.setColor(getRandColor(120,240));
 	for(int i=0;i<100;i++){
 		int x=r.nextInt(width);
 		int y=r.nextInt(height);
 		gc.drawOval(x,y,0,0);
 	}
 	
 //隨機產生4位數字的驗證碼
 	String RS="";
 	String rn="";
 	for(int i=0;i<6;i++){
 		//產生10以內的隨機數字rn
 		rn=String.valueOf(r.nextInt(10));
 		RS+=rn;
 		//將認證碼用drawString函數顯示到圖像里
 		gc.setColor(new Color(20+r.nextInt(110),20+r.nextInt(110),20+r.nextInt(110)));
 		gc.drawString(rn,13*i+6,16);
 		}
 //釋放圖形上下文環境
 	gc.dispose();
 
 //將認證碼RS存放到session中共享
 	session.setAttribute("random",RS);
 	
 //輸出生成后的驗證碼圖像到頁面
 	ImageIO.write(pic,"JPEG",response.getOutputStream());
 	
  %>