CodeServlet：

@WebServlet(name = "codeServlet",urlPatterns = "/codeServlet")
public class CodeServlet extends HttpServlet {

	private static final long serialVersionUID = 1L;

	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		doGet(request, response);
	}

	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		response.setContentType("image/png");
		response.setHeader("Pragma", "no-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);
		HttpSession session = request.getSession();

		int width = 60;
		int height = 20;
		String w = request.getParameter("w");
		String h = request.getParameter("h");
		if (StringUtils.isNumericSpace(w)) {
			width = Integer.parseInt(w);
		}
		if (StringUtils.isNumericSpace(h)) {
			height = Integer.parseInt(h);
		}

		int fontSize = getFontSize(width, height);
		BufferedImage image = new BufferedImage(width, height,
				BufferedImage.TYPE_INT_RGB);
		Graphics g = image.getGraphics();
		Random random = new Random();
		g.setColor(getRandColor(200, 250));
		g.fillRect(0, 0, width, height);
		g.setFont(new Font("Verdana", Font.BOLD, fontSize));
		g.setColor(getRandColor(160, 200));
		for (int i = 0; i < 155; 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);
		}

		String authCode = RandomStringUtils.random(4, true, false);
		for (int i = 0; i < authCode.length(); i++) {
			g.setColor(new Color(20 + random.nextInt(110), 20 + random
					.nextInt(110), 20 + random.nextInt(110)));
			g.drawString(String.valueOf(authCode.charAt(i)), fontSize * i,
					fontSize);
		}
		g.dispose();
		ImageIO.write(image, "png", response.getOutputStream());
		session.setAttribute("AUTH_CODE", authCode);
	}

	private Color getRandColor(int fc, int bc) {
		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);
	}

	private int getFontSize(int width, int height) {
		int fontSize = (width + 10) / 4;
		int h = height - 4;
		if (fontSize > h) {
			fontSize = h;
		}
		return fontSize;
	}

}

在WebMvcConfig 添加注解：

@ServletComponentScan(basePackages = {"com.demo.frame.common.servlet"})