<%@ page contentType="image/JPEG"  
    import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"  
    pageEncoding="GBK"%>  
<%!Color getRandColor(int fc, int bc) {//給定範圍獲得隨機顏色   
        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);   
    }%>  
<%   
    //設定頁面不快取   
    response.setHeader("Pragma", "No-cache");   
    response.setHeader("Cache-Control", "no-cache");   
    response.setDateHeader("Expires", 0);   

    // 在記憶體中建立圖象   
    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);   

    //設定字型   
    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條幹擾線，使圖象中的認證碼不易被其它程式探測到   
    g.setColor(getRandColor(160, 200));   
    for (int i = 0; i < 100; 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)));//呼叫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("code", sRand);   

    // 圖象生效   
    g.dispose();   

    // 輸出圖象到頁面   
    ImageIO.write(image, "JPEG", response.getOutputStream());   
%>