CacheFilter.java

package org.sigmah.server.servlet.filter;

/*
 * #%L
 * Sigmah
 * %%
 * Copyright (C) 2010 - 2016 URD
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public
 * License along with this program.  If not, see
 * <http://www.gnu.org/licenses/gpl-3.0.html>.
 * #L%
 */


import java.io.IOException;
import java.util.Date;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.lang3.StringUtils;

import com.google.inject.Singleton;

/**
 * <p>
 * Instructs browsers to cache application ressources "until the sun explodes" (or actually a year). Exceptions are made
 * for files containing the token ".nocache."
 * </p>
 * <p>
 * See http://www.infoq.com/articles/gwt-high-ajax
 * See http://www.gwtproject.org/doc/latest/DevGuideCompilingAndDebugging.html#perfect_caching
 * </p>
 * <p>
 * Apache configuration example:
 * 
 * <pre>
 * <Files *.nocache.*>
 *   ExpiresActive on
 *   ExpiresDefault "now"
 *   Header merge Cache-Control "public, max-age=0, must-revalidate"
 * </Files>
 * 		
 * <Files *.cache.*>
 *   ExpiresActive on
 *   ExpiresDefault "now plus 1 year"
 *   Header set dumbHeader "dumb header flag to control filter mechanism."
 * </Files>
 * </pre>
 * 
 * </p>
 * 
 * @author Denis Colliot (dcolliot@ideia.fr)
 */
@Singleton
public class CacheFilter implements Filter {

	/**
	 * Resources containing one of these value(s) will <b>never</b> be cached.
	 * 
	 * @see #containsAny(String, String...)
	 */
	private static final String[] NO_CACHE_FILTERS = { ".nocache.", "manifest" };

	/**
	 * Resources containing one of these value(s) will be cached.
	 * 
	 * @see #containsAny(String, String...)
	 */
	private static final String[] CACHE_FILTERS = { ".cache.", "/gxt" };

	/**
	 * Year period in milliseconds.
	 */
	private static final long YEAR = 365 * 24 * 60 * 60 * 1000L;

	/**
	 * Sigmah custom header.
	 * Used to control that responses headers are correctly set.
	 */
	private static final String CUSTOM_HEADER_NAME = "sigmahHeader";

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain filterChain) throws IOException, ServletException {

		if (!(request instanceof HttpServletRequest) || !(response instanceof HttpServletResponse)) {
			// Just in case.
			filterChain.doFilter(request, response);
			return;
		}

		final HttpServletRequest httpRequest = (HttpServletRequest) request;
		final HttpServletResponse httpResponse = (HttpServletResponse) response;
		final String requestURI = httpRequest.getRequestURI();

		if (containsAny(requestURI, CACHE_FILTERS)) {
			// Cached resource.
			httpResponse.setDateHeader("Expires", new Date().getTime() + YEAR);

			// Control flag.
			httpResponse.setHeader(CUSTOM_HEADER_NAME, "Resource cached by Sigmah filter.");

		} else if (containsAny(requestURI, NO_CACHE_FILTERS)) {
			// Never cached resource.
			httpResponse.setDateHeader("Expires", 0);
			httpResponse.setHeader("Cache-Control", "no-cache, public, max-age=0, must-revalidate");

			// Set IE extended HTTP/1.1 no-cache headers (use addHeader).
			httpResponse.addHeader("Cache-Control", "post-check=0, pre-check=0");

			// Set standard HTTP/1.0 no-cache header.
			httpResponse.setHeader("Pragma", "no-cache");

			// Control flag.
			httpResponse.setHeader(CUSTOM_HEADER_NAME, "Resource NOT cached by Sigmah filter.");
		}
		
		// Define content-type for JSON files.
		if(requestURI.contains(".json")) {
			httpResponse.setContentType("application/json");
		}

		filterChain.doFilter(request, response);
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void init(final FilterConfig filterConfig) throws ServletException {
		// Nothing to initialize.
	}

	/**
	 * {@inheritDoc}
	 */
	@Override
	public void destroy() {
		// Nothing to destroy.
	}

	/**
	 * Returns if the given {@code seq} contains any of the given {@code searchSeqs}.
	 * The search is case insensitive.
	 * 
	 * <pre>
	 * containsAny(null, null) → false
	 * containsAny(*, null) → false
	 * containsAny(null, *) → false
	 * containsAny("abc", "a") → true
	 * containsAny("abc", "abcd", "efg") → false
	 * containsAny("abc", "aB") → true
	 * containsAny("abc", "aBk") → false
	 * containsAny("abc", "aBk", "abC") → true
	 * </pre>
	 * 
	 * @param seq
	 *          The sequence.
	 * @param searchSeqs
	 *          The search sequence(s).
	 * @return {@code true} if the given {@code seq} contains any of the given {@code searchSeqs}, {@code false}
	 *         otherwise.
	 */
	private static boolean containsAny(final String seq, final String... searchSeqs) {

		if (seq == null || searchSeqs == null) {
			return false;
		}

		for (final String searchSeq : searchSeqs) {
			if (StringUtils.containsIgnoreCase(seq, searchSeq)) {
				return true;
			}
		}

		return false;
	}

}