servlet向浏览器输出验证码图片

servlet向浏览器输出验证码图片,注册页面的<img> 标签的src属性只需要指向该servlet即可

public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		//通知浏览器不要缓存图片
		response.setHeader("Expires", "-1");
		response.setHeader("Cache-Control", "no-cache");
		response.setHeader("Pragma", "no-cache");
		//通知浏览器以图片方式打开
		response.setHeader("Content-type", "image/jpeg");
		//在内存中创建一张图片
		BufferedImage image = new BufferedImage(100, 20, BufferedImage.TYPE_INT_RGB);
		//得到图片
		Graphics2D  g = (Graphics2D) image.getGraphics();

<span style="white-space:pre">		</span>//设置背景色
		g.setColor(Color.WHITE);
		g.fillRect(0, 0, 100, 20);
		//向图片上写数据
		g.setColor(Color.GRAY);
		g.setFont(new Font(null,Font.BOLD,20));
		g.drawString(makeNum(), 0, 20);
		//写到浏览器
		ImageIO.write(image, "jpg", response.getOutputStream());
	}

	private String makeNum() {
		Random r = new Random();
		String num = r.nextInt(9999) + "";
		for (int i = 0; i < 4 - num.length(); i++)
		{
			num += r.nextInt(9) ;
		}
		return num;
	}