<!--
實現登陸驗證碼，隨機生成4個數字并顯示于圖像之中 createMa.jsp
-->



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

<%!
Color getRandColor(int fc,int bc){		//在確定的范圍中獲得隨機顏色
        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);
        }
%>

<%								//設置頁面不緩存
response.setHeader("Pragma","No-cache");
response.setHeader("Cache-Control","no-cache");
response.setDateHeader("Expires", 0);

//在內存中創建圖象
int width=60, height=20;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
 								//獲取圖形上下文
Graphics g = image.getGraphics();
								//生成隨機類
Random random = new Random();
 								//設定背景色
g.setColor(getRandColor(200,250));
g.fillRect(0, 0, width, height);
								//設定字體
g.setFont(new Font("Times New Roman",Font.PLAIN,18));
								//隨機產生50條干擾線，使圖象中的認證碼不易被其它程序探測到
g.setColor(getRandColor(160,200));
for (int i=0;i<50;i++){
	int x = random.nextInt(width);
	int y = random.nextInt(height);
  int xl = random.nextInt(width);
  int yl = random.nextInt(height);
	g.drawLine(x,y,x+xl,y+yl);
}
		
								//取隨機產生的認證碼(4位數字)
String sRand="";
for (int i=0;i<4;i++){
    String rand=String.valueOf(random.nextInt(10));
    sRand+=rand;
    								//將認證碼顯示到圖象中
g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
								//調用函數出來的顏色相同，可能是因為種子太接近，所以只能直接生成
    g.drawString(rand,13*i+6,16);
}
 								//將認證碼存入SESSION
session.setAttribute("rand",sRand);
 								//圖象生效
g.dispose();
								
								//輸出圖象到頁面
ImageIO.write(image, "JPEG", response.getOutputStream());
%>