Clock.java

/*******************************************************************************
 * gMix open source project - https://svs.informatik.uni-hamburg.de/gmix/
 * Copyright (C) 2014  SVS
 *
 * 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/>.
 *******************************************************************************/
package staticContent.framework.clock;

import staticContent.framework.config.Settings;


/**
 * Provides a clock, which can be synchronized with a SNTP server (See RFC 
 * 2030 for further information).
 * <p>
 * Can retrieve SNTP messages from a SNTP server at regular intervals and 
 * calculate the local clock's offset each time. The local clock's offset 
 * calculation is implemented according to the SNTP algorithm specified in RFC 
 * 2030.  
 * <p>
 * The method <code>getTime()</code> can be used to generate timestamps (The 
 * typical accuracy of a SNTP client/server exchange is fractions of a second).
 * <p>
 * The System's time is never changed.
 * <p>
 * Uses Adam Buckley's class <code>NtpMessage</code> as message format.
 * 
 * @see NtpMessage
 */
public class Clock {

	private boolean useSNTPclock;
	private NtpClock ntpClock;
	
	
	public Clock(Settings settings) {
		this.useSNTPclock = settings.getPropertyAsBoolean("USE_SYNCHRONIZED_CLOCK");
		if (useSNTPclock)
			this.ntpClock = new NtpClock(settings);
	}
	
	
	/**
	 * Returns the number of milliseconds since January 1, 1970, 00:00:00 
	 * GMT from a (synchronized) clock.
	 * 
	 * @return	The number of milliseconds since January 1, 1970, 00:00:00 GMT.
	 */
	public long getTime() {
		if (useSNTPclock)
			return ntpClock.getTime();
		else
			return System.currentTimeMillis();
	}
	
}