Servlet生成随机验证码图片

1、servlet：

@SuppressWarnings("serial")
public class CheckCodeServlet extends HttpServlet {

	@Override
	protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		generateCode(response);
	}
	
	private void generateCode(HttpServletResponse response) throws ServletException, IOException {
		// 输出验证码图片
		/*
		 * step1.绘图
		 */
		// 先创建一个画布(内存映像对象)
		BufferedImage image = new BufferedImage(80, 30, BufferedImage.TYPE_INT_RGB);
		// 获得画笔
		Graphics g = image.getGraphics();
		// 设置画笔颜色，用来画背景
		g.setColor(new Color(255, 255, 255));
		// 给画布设置背景
		g.fillRect(0, 0, 100, 30);
		// 再次设置画笔颜色，用来画前景
		Random r = new Random();
		g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));
		// 设置字体(字体,风格,大小)
		g.setFont(new Font("微软雅黑", Font.BOLD | Font.ITALIC, 22));
		// 生成验证码
		String number = getNumber(r, 5);
		System.out.println("number:" + number);
		// 将验证码(number)绑定到session对象上
		//Session session = request.getSession();
		//session.setAttribute("number", number);
		// 在画布上绘图
		g.drawString(number, 1, 25);// 此处的1和25是左下角的坐标
		// 加一些干扰线
		for (int i = 0; i < 8; i++) {
			g.setColor(new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255)));
			g.drawLine(r.nextInt(80), r.nextInt(30), r.nextInt(80), r.nextInt(30));
		}
		/*
		 * step2.将图片压缩，然后输出，发送给客户端
		 */
		// 设置消息头:content-type:image/jpeg
		response.setContentType("image/jpeg");
		// 获得字节输出流(图片是二进制数据)
		OutputStream os = response.getOutputStream();
		// 将原始图片(image)按照指定的算法压缩(jpeg),将压缩之后得到的字节写入response对象
		ImageIO.write(image, "jpeg", os);
		os.close();
	}
	
	private String getNumber(Random r, int size) {
		StringBuilder sb = new StringBuilder();
		String chars = "0123456789abcdefghijklmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ";
		for (int i = 0; i < size; i++) {
			sb.append(chars.charAt(r.nextInt(chars.length())));
		}
		return sb.toString();
	}
}

2、html：

注：加上随机数Math.random()是为了解决浏览器缓存的问题！