透过filter实现对输出内容的压缩处理

通过filter实现对输出内容的压缩处理
在实际当中大量的js和页面内容使得页面呈现要花很长时间，特别是使用ext。如是找到这种办法去处理一下，还没有测试有多大的优化性能。全部实现代码在附件中

public class CompressionFilter implements Filter {
	// 适合在上JBoss, Jetty, JOnAS, OC4J, Orion,and Tomcat,其它的可能有bug
	static boolean useFilter = true;

	public static final String ENCODING = "UTF-8";
	
	private static final String _GZIP = "gzip";
	
	private static final String _ALREADY_FILTERED = CompressionFilter.class.getName() + "_ALREADY_FILTERED";

	private static final String _COMPRESS = "compress";
	
	public static String[] BOOLEANS = {"true", "t", "y", "on", "1"};

	private static Log _log = LogFactory.getLog(CompressionFilter.class);

	public void init(FilterConfig config) {
	}

	public void doFilter(
			ServletRequest req, ServletResponse res, FilterChain chain)
		throws IOException, ServletException {

		if (_log.isDebugEnabled()) {
			if (useFilter) {
				_log.debug("Compression is enabled");
			}
			else {
				_log.debug("Compression is disabled");
			}
		}

		HttpServletRequest httpReq = (HttpServletRequest)req;
		HttpServletResponse httpRes = (HttpServletResponse)res;

		String completeURL = httpReq.getRequestURL().toString();

		if (useFilter && isCompress(httpReq) && !isInclude(httpReq) &&
			acceptsGzip(httpReq) && !isAlreadyFiltered(httpReq)) {

			if (_log.isDebugEnabled()) {
				_log.debug("Compressing " + completeURL);
			}

			httpReq.setAttribute(_ALREADY_FILTERED, Boolean.TRUE);

			CompressionResponse compressionResponse =
				new CompressionResponse(httpRes);

			chain.doFilter(req, compressionResponse);

			compressionResponse.finishResponse();
		}
		else {
			if (_log.isDebugEnabled()) {
				_log.debug("Not compressing " + completeURL);
			}

			chain.doFilter(req, res);
		}
	}

	public void destroy() {
	}

	protected boolean isAlreadyFiltered(HttpServletRequest req) {
		if (req.getAttribute(_ALREADY_FILTERED) != null) {
			return true;
		}
		else {
			return false;
		}
	}

	protected boolean isCompress(HttpServletRequest req) {
		if (!getBoolean(req.getParameter(_COMPRESS), true)) {
			return false;
		}
		else {
			return true;
		}
	}

	protected boolean isInclude(HttpServletRequest req) {
		String uri = (String)req.getAttribute("javax.servlet.include.request_uri");
		if (uri == null) {
			return false;
		}
		else {
			return true;
		}
	}
	
	protected boolean acceptsGzip(HttpServletRequest req) {
		String acceptEncoding = req.getHeader("Accept-Encoding");
		if ((acceptEncoding != null) &&
			(acceptEncoding.indexOf(_GZIP) != -1)) {
			return true;
		}
		else {
			return false;
		}
	}
	
	protected boolean getBoolean(String value, boolean defaultValue) {
		if (value != null) {
			try {
				value = value.trim();

				if (value.equalsIgnoreCase(BOOLEANS[0]) ||
					value.equalsIgnoreCase(BOOLEANS[1]) ||
					value.equalsIgnoreCase(BOOLEANS[2]) ||
					value.equalsIgnoreCase(BOOLEANS[3]) ||
					value.equalsIgnoreCase(BOOLEANS[4])) {

					return true;
				}
				else {
					return false;
				}
			}
			catch (Exception e) {
			}
		}

		return defaultValue;
	}
}