web 服务端取得访问某个页面返回值的问题

目标：
　　访问 http://localhost/preview/a.css 的时候，如果 preview 中并没有 a.css 这个文件，就接着访问 html/a.css


解决办法：
　　在filter 中 wraper 了 response ，得到 error code，发现是 404，就接着访问下一个。代码如下：
　　我觉得挺土的，有没有好办法取得 response 的 error code 呢？或是其它方法解决这个问题？

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException,
			ServletException {
		HttpServletRequest req = (HttpServletRequest) request;
		HttpServletResponse resp = (HttpServletResponse) response;
		ServletResponseWraper wraper = new ServletResponseWraper(resp);
		chain.doFilter(request, wraper);
		if (wraper.getStatus() == HttpServletResponse.SC_NOT_FOUND) {
			if (isPreview(req)) {
				String path = getHtmlUrl(req);
				wraper.status = HttpServletResponse.SC_OK;
				req.getRequestDispatcher(path).forward(req, wraper);
			} else {
				wraper.getResponse().sendError(wraper.getStatus(), wraper.getRootMessage());
			}
		}
	}

	private String getHtmlUrl(HttpServletRequest req) {
		String path = req.getRequestURI().replaceFirst(req.getContextPath(), "");
		path = path.replaceFirst("/preview", "");
		path = "/html" + path;
		return path;
	}

	private boolean isPreview(HttpServletRequest req) {
		String path = req.getRequestURI().replaceFirst(req.getContextPath(), "");
		boolean isPreview = path.startsWith("/preview");
		return isPreview;
	}

	private class ServletResponseWraper implements HttpServletResponse {
		private HttpServletResponse response;
		private int status = HttpServletResponse.SC_OK;
		private String msg;
		private String rootMessage;

		public ServletResponseWraper(HttpServletResponse response) {
			while (response instanceof ServletResponseWraper) {
				ServletResponseWraper wraper = (ServletResponseWraper) response;
				setRootMessage(wraper.getRootMessage());
				setMessage(wraper.getMessage());
				response = wraper.getResponse();
			}
			this.response = response;
		}

		public HttpServletResponse getResponse() {
			return response;
		}

		public void setRootMessage(String message) {
			if (rootMessage == null)
				rootMessage = message;
		}

		public String getRootMessage() {
			return rootMessage;
		}

		public int getStatus() {
			return status;
		}

		public String getMessage() {
			return msg;
		}

		public void setMessage(String message) {
			setRootMessage(message);
			msg = message;
		}

...
		public void sendError(int sc, String msg) throws IOException {
			status = sc;
			setMessage(msg);
			//			response.sendError(sc, msg);
		}

		public void sendError(int sc) throws IOException {
			status = sc;
			//			response.sendError(sc);
		}

...
	}