src/java/grails/plugin/cache/web/HttpDateFormatter.java

/* Copyright 2012-2013 SpringSource.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package grails.plugin.cache.web;

import java.io.Serializable;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

import org.slf4j.LoggerFactory;

/**
 * RFC 2616 - HTTP/1.1 Protocol
 * <p/>
 * Section 3.3.1 defines the preferred full date and time as:
 *
 * <pre>
 * HTTP-date    = rfc1123-date
 * rfc1123-date = wkday "," SP date1 SP time SP "GMT"
 * date1        = 2DIGIT SP month SP 4DIGIT
 * ; day month year (e.g., 02 Jun 1982)
 * time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
 * ; 00:00:00 - 23:59:59
 * wkday        = "Mon" | "Tue" | "Wed"
 * | "Thu" | "Fri" | "Sat" | "Sun"
 * month        = "Jan" | "Feb" | "Mar" | "Apr"
 * | "May" | "Jun" | "Jul" | "Aug"
 * | "Sep" | "Oct" | "Nov" | "Dec"
 * </pre>
 * <p/>
 * An example is <code>Sun, 06 Nov 1994 08:49:37 GMT</code>
 * <p/>
 * These are used in request and response headers.
 * <p/>
 *
 * Based on net.sf.ehcache.constructs.web.HttpDateFormatter.
 *
 * @author Greg Luck
 * @author Burt Beckwith
 */
public class HttpDateFormatter implements Serializable {

	private static final long serialVersionUID = 1;

	protected final SimpleDateFormat httpDateFormat = new SimpleDateFormat(
			"EEE, dd MMM yyyy HH:mm:ss z", Locale.US);

	/**
	 * Constructs a new formatter.
	 * <p/>
	 * Note that this class is not thread-safe for use by multiple threads, as
	 * SimpleDateFormat is not. Each thread should create their own instance of
	 * this class.
	 */
	public HttpDateFormatter() {
		httpDateFormat.setTimeZone(TimeZone.getTimeZone("GMT"));
	}

	/**
	 * @param date
	 * @return A date formatted in accordance with Section 3.3.1 of RFC 2616
	 */
	public synchronized String formatHttpDate(Date date) {
		return httpDateFormat.format(date);
	}

	/**
	 * Parses dates supplied in accordance with Section 3.3.1 of RFC 2616
	 *
	 * @param date
	 *           a date formatted in accordance with Section 3.3.1 of RFC 2616
	 * @return the parsed Date. If the date cannot be parsed, the start of POSIX
	 *         time, 1/1/1970 is returned, which will have the effect of expiring
	 *         the content.
	 */
	public synchronized Date parseDateFromHttpDate(String date) {
		try {
			return httpDateFormat.parse(date);
		}
		catch (ParseException e) {
			LoggerFactory.getLogger(getClass()).debug(
					"ParseException on date {}. 1/1/1970 will be returned", date);
			return new Date(0);
		}
	}
}