TimeConverter - converts Strings like "11w8d12h3m12s49ms" into milliseconds

TimeConverter.java

package org.outofrange.timeconverter;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class TimeConverter {
	private static final Pattern PATTERN = Pattern.compile("(\\d+)([A-Za-z]+)");

	private TimeConverter() { }

	public static long toMillis(String input) {
		long sum = 0;

		for (Duration d : getDurationParts(input)) {
			sum += d.toMillis();
		}

		return sum;
	}

	private static List<Duration> getDurationParts(String input) {
		final List<Duration> durations = new ArrayList<>();

		final Matcher matcher = PATTERN.matcher(input);
		while (matcher.find()) {
			final long value = Long.valueOf(matcher.group(1));
			final TimeStringUnit timeStringUnit = TimeStringUnit.forChars(matcher.group(2));
			durations.add(new Duration(value, timeStringUnit));
		}

		return durations;
	}

	private static class Duration {
		private final long value;
		private final TimeStringUnit timeStringUnit;

		public Duration(long value, TimeStringUnit timeStringUnit) {
			this.value = value;
			this.timeStringUnit = timeStringUnit;
		}

		public long toMillis() {
			return timeStringUnit.toMillis(value);
		}
	}

	private enum TimeStringUnit {
		WEEKS("w") { public long toMillis(long d) { return 7 * TimeUnit.DAYS.toMillis(d); } },
		DAYS("d") { public long toMillis(long d) { return TimeUnit.DAYS.toMillis(d); } },
		HOURS("h") { public long toMillis(long d) { return TimeUnit.HOURS.toMillis(d); } },
		MINUTES("m") { public long toMillis(long d) { return TimeUnit.MINUTES.toMillis(d); } },
		SECONDS("s") { public long toMillis(long d) { return TimeUnit.SECONDS.toMillis(d); } },
		MILLISECONDS("ms") { public long toMillis(long d) { return d; } };

		private final String unit;

		TimeStringUnit(String unit) {
			this.unit = unit;
		}

		public String getUnit() {
			return unit;
		}

		public long toMillis(long d) {
			throw new AbstractMethodError();
		}

		public static TimeStringUnit forChars(String unit) {
			for (TimeStringUnit timeStringUnit : TimeStringUnit.values()) {
				if (timeStringUnit.getUnit().equals(unit)) {
					return timeStringUnit;
				}
			}

			throw new IllegalArgumentException();
		}
	}
}