生成验证图片

    private void createImage(OutputStream out) {
        int width = 100;
        int height = 60;
        BufferedImage bimage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        Graphics2D g = bimage.createGraphics();
        //设置背景色
        g.setBackground(Color.WHITE);
        g.clearRect(0, 0, width, height);

        g.setColor(Color.GRAY);
        g.drawRect(0, 0, width - 1, height - 1);

        //绘制背景线条
        Random random = new Random();
        g.setColor(new Color(random.nextInt(40) + 160, random.nextInt(40) + 160, random.nextInt(40) + 160));
        for (int i = 0; i < 120; 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);
        }

        //绘制随机数值
        String str = "";
        int[] ns = {10, 26, 26, 48, 65, 97};
        for (int i = 0; i < 6; i++) {
            int n = (int) (random.nextInt(3));
            String s = String.valueOf((char) (random.nextInt(ns[n]) + ns[n + 3]));
            str += s;
            g.setFont(new Font("Arial", random.nextInt(3), 15 + random.nextInt(10)));
            g.setColor(new Color((int) (Math.random() * 255), (int) (Math.random() * 255), (int) (Math.random() * 255)));
            g.drawString(s, (5 + i * 15), random.nextInt(10) + 30);
        }
        System.out.println(str);
        
        g.dispose();
        bimage.flush();
        
        //编码生成jpeg图片
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
        JPEGEncodeParam param = encoder.getDefaultJPEGEncodeParam(bimage);
        param.setQuality(1.0f, false);
        encoder.setJPEGEncodeParam(param);
        try {
            encoder.encode(bimage);
        } catch (IOException ioe) {
            ioe.printStackTrace();
        }
    }