<%
	OutputStream o = response.getOutputStream();
%>
<%@ page language="java" import="java.util.*" pageEncoding="gbk"%>
<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*,java.io.OutputStream" %>

<%!Color getRandColor(int fc, int bc) {//給定范圍獲得隨機顏色
		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);
	response.setContentType("image/jpeg");

	// 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));

	//畫邊框
	//g.setColor(new Color());
	//g.drawRect(0,0,width-1,height-1);

	// 隨機產生155條干擾線，使圖象中的認證碼不易被其它程序探測到
	for (int i = 0; i < 20; i++) {
		int x2 = random.nextInt(width);
		int y2 = random.nextInt(height);
		int x3 = random.nextInt(12);
		int y3 = random.nextInt(12);
		g.drawLine(x2, y2, x2 + x3, y2 + y3);
	}

	// 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)));
	//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(12);
		int yl = random.nextInt(12);
		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", o);
	o.flush();
	out.clear();
	out = pageContext.pushBody();
%>