timestamp.java

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package org.apache.commons.net.ntp;
/*
 * Copyright 2001-2005 The Apache Software Foundation
 *
 * 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.
 */


import java.util.TimeZone;
import java.util.Date;
import java.util.Locale;
import java.lang.ref.SoftReference;
import java.text.SimpleDateFormat;
import java.text.DateFormat;

/***
 * TimeStamp class represents the Network Time Protocol (NTP) timestamp
 * as defined in RFC-1305 and SNTP (RFC-2030). It is represented as a
 * 64-bit unsigned fixed-point number in seconds relative to 0-hour on 1-January-1900.
 * The 32-bit low-order bits are the fractional seconds whose precision is
 * about 200 picoseconds. Assumes overflow date when date passes MAX_LONG
 * and reverts back to 0 is 2036 and not 1900. Test for most significant
 * bit: if MSB=0 then 2036 basis is used otherwise 1900 if MSB=1.
 * <p>
 * Methods exist to convert NTP timestamps to and from the equivalent Java date
 * representation, which is the number of milliseconds since the standard base
 * time known as "the epoch", namely January 1, 1970, 00:00:00 GMT.
 * </p>
 *
 * @author Jason Mathews, MITRE Corp
 * @version $Revision: 165675 $ $Date: 2005-05-02 15:09:55 -0500 (Mon, 02 May 2005) $
 * @see java.util.Date
 */
public class TimeStamp implements java.io.Serializable, Comparable
{

    /**
     * baseline NTP time if bit-0=0 -> 7-Feb-2036 @ 06:28:16 UTC
     */
    protected static final long msb0baseTime = 2085978496000L;

    /**
     *  baseline NTP time if bit-0=1 -> 1-Jan-1900 @ 01:00:00 UTC
     */
    protected static final long msb1baseTime = -2208988800000L;

    /**
     * Default NTP date string format. E.g. Fri, Sep 12 2003 21:06:23.860.
     * See <code>java.text.SimpleDateFormat</code> for code descriptions.
     */
    public final static String NTP_DATE_FORMAT = "EEE, MMM dd yyyy HH:mm:ss.SSS";

    /*
     * Caches for the DateFormatters used by various toString methods.
     */
    private static SoftReference simpleFormatter = null;
    private static SoftReference utcFormatter = null;

    /**
     * NTP timestamp value: 64-bit unsigned fixed-point number as defined in RFC-1305
     * with high-order 32 bits the seconds field and the low-order 32-bits the
     * fractional field.
     */
    private long ntpTime;

    private static final long serialVersionUID = 8139806907588338737L;

    // initialization of static time bases
    /*
    static {
        TimeZone utcZone = TimeZone.getTimeZone("UTC");
        Calendar calendar = Calendar.getInstance(utcZone);
        calendar.set(1900, Calendar.JANUARY, 1, 0, 0, 0);
        calendar.set(Calendar.MILLISECOND, 0);
        msb1baseTime = calendar.getTime().getTime();
        calendar.set(2036, Calendar.FEBRUARY, 7, 6, 28, 16);
        calendar.set(Calendar.MILLISECOND, 0);
        msb0baseTime = calendar.getTime().getTime();
    }
    */

    /***
     * Constructs a newly allocated NTP timestamp object
     * that represents the native 64-bit long argument.
     */
    public TimeStamp(long ntpTime)
    {
        this.ntpTime = ntpTime;
    }

    /***
     * Constructs a newly allocated NTP timestamp object
     * that represents the value represented by the string
     * in hexdecimal form (e.g. "c1a089bd.fc904f6d").
     *
     * @throws NumberFormatException - if the string does not contain a parsable timestamp.
     */
    public TimeStamp(String s) throws NumberFormatException
    {
        ntpTime = decodeNtpHexString(s);
    }

    /***
     * Constructs a newly allocated NTP timestamp object
     * that represents the Java Date argument.
     *
     * @param d - the Date to be represented by the Timestamp object.
     */
    public TimeStamp(Date d)
    {
        ntpTime = (d == null) ? 0 : toNtpTime(d.getTime());
    }

    /***
     * Returns the value of this Timestamp as a long value.
     *
     * @return the 64-bit long value represented by this object.
     */
    public long ntpValue()
    {
        return ntpTime;
    }

    /***
     * Returns high-order 32-bits representing the seconds of this NTP timestamp.
     *
     * @return seconds represented by this NTP timestamp.
     */
    public long getSeconds()
    {
        return (ntpTime >>> 32) & 0xffffffffL;
    }

    /***
     * Returns low-order 32-bits representing the fractional seconds.
     *
     * @return fractional seconds represented by this NTP timestamp.
     */
    public long getFraction()
    {
        return ntpTime & 0xffffffffL;
    }

    /***
     * Convert NTP timestamp to Java standard time.
     *
     * @return NTP Timestamp in Java time
     */
    public long getTime()
    {
        return getTime(ntpTime);
    }

    /***
     * Convert NTP timestamp to Java Date object.
     *
     * @return NTP Timestamp in Java Date
     */
    public Date getDate()
    {
        long time = getTime(ntpTime);
        return new Date(time);
    }

    /***
     * Convert 64-bit NTP timestamp to Java standard time.
     *
     * Note that java time (milliseconds) by definition has less precision
     * then NTP time (picoseconds) so converting NTP timestamp to java time and back
     * to NTP timestamp loses precision. For example, Tue, Dec 17 2002 09:07:24.810 EST
     * is represented by a single Java-based time value of f22cd1fc8a, but its
     * NTP equivalent are all values ranging from c1a9ae1c.cf5c28f5 to c1a9ae1c.cf9db22c.
     *
     * @param ntpTimeValue
     * @return the number of milliseconds since January 1, 1970, 00:00:00 GMT
     * represented by this NTP timestamp value.
     */
    public static long getTime(long ntpTimeValue)
    {
        long seconds = (ntpTimeValue >>> 32) & 0xffffffffL;	// high-order 32-bits
        long fraction = ntpTimeValue & 0xffffffffL;		// low-order 32-bits

        // Use round-off on fractional part to preserve going to lower precision
        fraction = Math.round(1000D * fraction / 0x100000000L);

        /*
         * If the most significant bit (MSB) on the seconds field is set we use
         * a different time base. The following text is a quote from RFC-2030 (SNTP v4):
         *
         *  If bit 0 is set, the UTC time is in the range 1968-2036 and UTC time
         *  is reckoned from 0h 0m 0s UTC on 1 January 1900. If bit 0 is not set,
         *  the time is in the range 2036-2104 and UTC time is reckoned from
         *  6h 28m 16s UTC on 7 February 2036.
         */
        long msb = seconds & 0x80000000L;
        if (msb == 0) {
            // use base: 7-Feb-2036 @ 06:28:16 UTC
            return msb0baseTime + (seconds * 1000) + fraction;
        } else {
            // use base: 1-Jan-1900 @ 01:00:00 UTC
            return msb1baseTime + (seconds * 1000) + fraction;
        }
    }

    /***
     * Helper method to convert Java time to NTP timestamp object.
     * Note that Java time (milliseconds) by definition has less precision
     * then NTP time (picoseconds) so converting Ntptime to Javatime and back
     * to Ntptime loses precision. For example, Tue, Dec 17 2002 09:07:24.810
     * is represented by a single Java-based time value of f22cd1fc8a, but its
     * NTP equivalent are all values from c1a9ae1c.cf5c28f5 to c1a9ae1c.cf9db22c.
     * @param   date   the milliseconds since January 1, 1970, 00:00:00 GMT.
     * @return NTP timestamp object at the specified date.
     */
    public static TimeStamp getNtpTime(long date)
    {
        return new TimeStamp(toNtpTime(date));
    }

    /***
     * Constructs a NTP timestamp object and initializes it so that
     * it represents the time at which it was allocated, measured to the
     * nearest millisecond.
     * @return NTP timestamp object set to the current time.
     * @see     java.lang.System#currentTimeMillis()
     */
    public static TimeStamp getCurrentTime()
    {
        return getNtpTime(System.currentTimeMillis());
    }

    /***
     * Convert NTP timestamp hexstring (e.g. "c1a089bd.fc904f6d") to the NTP