Package org.dspace.util

Class DateMathParser

  • public class DateMathParser
extends Object
    This class (Apache license) is copied from Apache Solr, adding some tweaks to resolve an unneeded dependency. See the original.

    A Simple Utility class for parsing "math" like strings relating to Dates.

    The basic syntax support addition, subtraction and rounding at various levels of granularity (or "units"). Commands can be chained together and are parsed from left to right. '+' and '-' denote addition and subtraction, while '/' denotes "round". Round requires only a unit, while addition/subtraction require an integer value and a unit. Command strings must not include white space, but the "No-Op" command (empty string) is allowed.... 

       /HOUR
      ... Round to the start of the current hour
   /DAY
      ... Round to the start of the current day
   +2YEARS
      ... Exactly two years in the future from now
   -1DAY
      ... Exactly 1 day prior to now
   /DAY+6MONTHS+3DAYS
      ... 6 months and 3 days in the future from the start of
          the current day
   +6MONTHS+3DAYS/DAY
      ... 6 months and 3 days in the future from now, rounded
          down to nearest day

    (Multiple aliases exist for the various units of time (ie: MINUTE and MINUTES; MILLI, MILLIS, MILLISECOND, and MILLISECONDS.) The complete list can be found by inspecting the keySet of CALENDAR_UNITS)

    All commands are relative to a "now" which is fixed in an instance of DateMathParser such that p.parseMath("+0MILLISECOND").equals(p.parseMath("+0MILLISECOND")) no matter how many wall clock milliseconds elapse between the two distinct calls to parse (Assuming no other thread calls "setNow" in the interim). The default value of 'now' is the time at the moment the DateMathParser instance is constructed, unless overridden by the NOW request parameter.

    All commands are also affected to the rules of a specified TimeZone (including the start/end of DST if any) which determine when each arbitrary day starts. This not only impacts rounding/adding of DAYs, but also cascades to rounding of HOUR, MIN, MONTH, YEAR as well. The default TimeZone used is UTC unless overridden by the TZ request parameter.

    Historical dates: The calendar computation is completely done with the Gregorian system/algorithm. It does not switch to Julian or anything else, unlike the default GregorianCalendar.

    See Also:
    SolrRequestInfo#getClientTimeZone, SolrRequestInfo#getNOW

    • Field Detail

      • DEFAULT_MATH_TZ

        public static final TimeZone DEFAULT_MATH_TZ
        Default TimeZone for DateMath rounding (UTC)

      • CALENDAR_UNITS

        public static final Map<String,​ChronoUnit> CALENDAR_UNITS
        A mapping from (uppercased) String labels identifying time units, to the corresponding ChronoUnit value (e.g. "YEARS") used to set/add/roll that unit of measurement.

        A single logical unit of time might be represented by multiple labels for convenience (i.e. DATE==DAYS, MILLI==MILLIS)

        See Also:
        Calendar

    • Constructor Detail

      • DateMathParser

        public DateMathParser()
        Default constructor that assumes UTC should be used for rounding unless otherwise specified in the SolrRequestInfo
        See Also:
        SolrRequestInfo#getClientTimeZone

      • DateMathParser

        public DateMathParser​(TimeZone tz)
        Parameters:
        tz - The TimeZone used for rounding (to determine when hours/days begin). If null, then this method defaults to the value dictated by the SolrRequestInfo if it exists -- otherwise it uses UTC.
        See Also:
        DEFAULT_MATH_TZ, Calendar.getInstance(TimeZone, Locale), SolrRequestInfo#getClientTimeZone

    • Method Detail

      • parseMath

        public static Date parseMath​(Date now,
                             String val)
                      throws Exception
        Parses a String which may be a date (in the standard ISO-8601 format) followed by an optional math expression.
        Parameters:
        now - an optional fixed date to use as "NOW"
        val - the string to parse
        Returns:
        result of applying the parsed expression to "NOW".
        Throws:
        Exception

      • getTimeZone

        public TimeZone getTimeZone()
        Returns:
        the time zone

      • setNow

        public void setNow​(Date n)
        Defines this instance's concept of "now".
        Parameters:
        n - new value of "now".
        See Also:
        getNow()

      • getNow

        public Date getNow()
        Returns a clone of this instance's concept of "now" (never null). If setNow was never called (or if null was specified) then this method first defines 'now' as the value dictated by the SolrRequestInfo if it exists -- otherwise it uses a new Date instance at the moment getNow() is first called.
        Returns:
        "now".
        See Also:
        setNow(java.util.Date), SolrRequestInfo#getNOW

      • parseMath

        public Date parseMath​(String math)
               throws ParseException
        Parses a date expression relative to "now".
        Parameters:
        math - a date expression such as "+24MONTHS".
        Returns:
        the result of applying the expression to the current time.
        Throws:
        ParseException - positions in ParseExceptions are token positions, not character positions.

      • main

        public static void main​(String[] argv)
                 throws Exception
        For manual testing. With one argument, test one-argument parseMath. With two (or more) arguments, test two-argument parseMath.
        Parameters:
        argv - date math expressions.
        Throws:
        Exception - passed through.