private Duration convert(String source, DurationStyle style, ChronoUnit unit) {
		style = (style != null) ? style : DurationStyle.detect(source);
		return style.parse(source, unit);
	}

	/**
	 * Simple formatting, for example '1s'.(簡(jiǎn)單格式)
	 */
	SIMPLE("^([+-]?\\d+)([a-zA-Z]{0,2})$") {
 
		......
	},
 
	/**
	 * ISO-8601 formatting. (ISO-8601格式)
	 */
	ISO8601("^[+-]?[pP].*$") {
 
		......
	};

	/**
	 * Units that we support.
	 */
	enum Unit {
 
		/**
		 * Nanoseconds.
		 */
		NANOS(ChronoUnit.NANOS, "ns", Duration::toNanos),
 
		/**
		 * Microseconds.
		 */
		MICROS(ChronoUnit.MICROS, "us", (duration) -> duration.toNanos() / 1000L),
 
		/**
		 * Milliseconds.
		 */
		MILLIS(ChronoUnit.MILLIS, "ms", Duration::toMillis),
 
		/**
		 * Seconds.
		 */
		SECONDS(ChronoUnit.SECONDS, "s", Duration::getSeconds),
 
		/**
		 * Minutes.
		 */
		MINUTES(ChronoUnit.MINUTES, "m", Duration::toMinutes),
 
		/**
		 * Hours.
		 */
		HOURS(ChronoUnit.HOURS, "h", Duration::toHours),
 
		/**
		 * Days.
		 */
		DAYS(ChronoUnit.DAYS, "d", Duration::toDays);

          "PT20.345S" -- parses as "20.345 seconds"
          "PT15M"     -- parses as "15 minutes" (where a minute is 60 seconds)
          "PT10H"     -- parses as "10 hours" (where an hour is 3600 seconds)
          "P2D"       -- parses as "2 days" (where a day is 24 hours or 86400 seconds)
          "P2DT3H4M"  -- parses as "2 days, 3 hours and 4 minutes"
          "PT-6H3M"    -- parses as "-6 hours and +3 minutes"
          "-PT6H3M"    -- parses as "-6 hours and -3 minutes"
          "-PT-6H+3M"  -- parses as "+6 hours and -3 minutes"

/**
     * Obtains a {@code Duration} from a text string such as {@code PnDTnHnMn.nS}.
     * <p>
     * This will parse a textual representation of a duration, including the
     * string produced by {@code toString()}. The formats accepted are based
     * on the ISO-8601 duration format {@code PnDTnHnMn.nS} with days
     * considered to be exactly 24 hours.
     * <p>
     * The string starts with an optional sign, denoted by the ASCII negative
     * or positive symbol. If negative, the whole period is negated.
     * The ASCII letter "P" is next in upper or lower case.
     * There are then four sections, each consisting of a number and a suffix.
     * The sections have suffixes in ASCII of "D", "H", "M" and "S" for
     * days, hours, minutes and seconds, accepted in upper or lower case.
     * The suffixes must occur in order. The ASCII letter "T" must occur before
     * the first occurrence, if any, of an hour, minute or second section.
     * At least one of the four sections must be present, and if "T" is present
     * there must be at least one section after the "T".
     * The number part of each section must consist of one or more ASCII digits.
     * The number may be prefixed by the ASCII negative or positive symbol.
     * The number of days, hours and minutes must parse to an {@code long}.
     * The number of seconds must parse to an {@code long} with optional fraction.
     * The decimal point may be either a dot or a comma.
     * The fractional part may have from zero to 9 digits.
     * <p>
     * The leading plus/minus sign, and negative values for other units are
     * not part of the ISO-8601 standard.
     * <p>
     * Examples:
     * <pre>
     *    "PT20.345S" -- parses as "20.345 seconds"
     *    "PT15M"     -- parses as "15 minutes" (where a minute is 60 seconds)
     *    "PT10H"     -- parses as "10 hours" (where an hour is 3600 seconds)
     *    "P2D"       -- parses as "2 days" (where a day is 24 hours or 86400 seconds)
     *    "P2DT3H4M"  -- parses as "2 days, 3 hours and 4 minutes"
     *    "P-6H3M"    -- parses as "-6 hours and +3 minutes"
     *    "-P6H3M"    -- parses as "-6 hours and -3 minutes"
     *    "-P-6H+3M"  -- parses as "+6 hours and -3 minutes"
     * </pre>
     *
     * @param text  the text to parse, not null
     * @return the parsed duration, not null
     * @throws DateTimeParseException if the text cannot be parsed to a duration
     */
    public static Duration parse(CharSequence text) {
        Objects.requireNonNull(text, "text");
        Matcher matcher = PATTERN.matcher(text);
        if (matcher.matches()) {
            // check for letter T but no time sections
            if ("T".equals(matcher.group(3)) == false) {
                boolean negate = "-".equals(matcher.group(1));
                String dayMatch = matcher.group(2);
                String hourMatch = matcher.group(4);
                String minuteMatch = matcher.group(5);
                String secondMatch = matcher.group(6);
                String fractionMatch = matcher.group(7);
                if (dayMatch != null || hourMatch != null || minuteMatch != null || secondMatch != null) {
                    long daysAsSecs = parseNumber(text, dayMatch, SECONDS_PER_DAY, "days");
                    long hoursAsSecs = parseNumber(text, hourMatch, SECONDS_PER_HOUR, "hours");
                    long minsAsSecs = parseNumber(text, minuteMatch, SECONDS_PER_MINUTE, "minutes");
                    long seconds = parseNumber(text, secondMatch, 1, "seconds");
                    int nanos = parseFraction(text,  fractionMatch, seconds < 0 ? -1 : 1);
                    try {
                        return create(negate, daysAsSecs, hoursAsSecs, minsAsSecs, seconds, nanos);
                    } catch (ArithmeticException ex) {
                        throw (DateTimeParseException) new DateTimeParseException("Text cannot be parsed to a Duration: overflow", text, 0).initCause(ex);
                    }
                }
            }
        }
        throw new DateTimeParseException("Text cannot be parsed to a Duration", text, 0);
    }