This class also helps you to limit the resolution of your dates. Do not + * save dates with a finer resolution than you really need, as then + * RangeQuery and PrefixQuery will require more memory and become slower. + * + *
Compared to {@link DateField} the strings generated by the methods
+ * in this class take slightly more space, unless your selected resolution
+ * is set to Resolution.DAY or lower.
+ *
+ *
+ * Another approach is {@link NumericUtils}, which provides
+ * a sortable binary representation (prefix encoded) of numeric values, which
+ * date/time are.
+ * For indexing a {@link Date} or {@link Calendar}, just get the unix timestamp as
+ * long using {@link Date#getTime} or {@link Calendar#getTimeInMillis} and
+ * index this as a numeric value with {@link NumericField}
+ * and use {@link NumericRangeQuery} to query it.
+ */
+public class DateTools {
+
+ final static TimeZone GMT = TimeZone.getTimeZone("GMT");
+
+ private static final ThreadLocalyyyyMMddHHmmssSSS or shorter,
+ * depending on resolution; using GMT as timezone
+ */
+ public static String dateToString(Date date, Resolution resolution) {
+ return timeToString(date.getTime(), resolution);
+ }
+
+ /**
+ * Converts a millisecond time to a string suitable for indexing.
+ *
+ * @param time the date expressed as milliseconds since January 1, 1970, 00:00:00 GMT
+ * @param resolution the desired resolution, see
+ * {@link #round(long, DateTools.Resolution)}
+ * @return a string in format yyyyMMddHHmmssSSS or shorter,
+ * depending on resolution; using GMT as timezone
+ */
+ public static String timeToString(long time, Resolution resolution) {
+ final Date date = new Date(round(time, resolution));
+ return TL_FORMATS.get()[resolution.formatLen].format(date);
+ }
+
+ /**
+ * Converts a string produced by timeToString or
+ * dateToString back to a time, represented as the
+ * number of milliseconds since January 1, 1970, 00:00:00 GMT.
+ *
+ * @param dateString the date string to be converted
+ * @return the number of milliseconds since January 1, 1970, 00:00:00 GMT
+ * @throws ParseException if dateString is not in the
+ * expected format
+ */
+ public static long stringToTime(String dateString) throws ParseException {
+ return stringToDate(dateString).getTime();
+ }
+
+ /**
+ * Converts a string produced by timeToString or
+ * dateToString back to a time, represented as a
+ * Date object.
+ *
+ * @param dateString the date string to be converted
+ * @return the parsed time as a Date object
+ * @throws ParseException if dateString is not in the
+ * expected format
+ */
+ public static Date stringToDate(String dateString) throws ParseException {
+ try {
+ return TL_FORMATS.get()[dateString.length()].parse(dateString);
+ } catch (Exception e) {
+ throw new ParseException("Input is not a valid date string: " + dateString, 0);
+ }
+ }
+
+ /**
+ * Limit a date's resolution. For example, the date 2004-09-21 13:50:11
+ * will be changed to 2004-09-01 00:00:00 when using
+ * Resolution.MONTH.
+ *
+ * @param resolution The desired resolution of the date to be returned
+ * @return the date with all values more precise than resolution
+ * set to 0 or 1
+ */
+ public static Date round(Date date, Resolution resolution) {
+ return new Date(round(date.getTime(), resolution));
+ }
+
+ /**
+ * Limit a date's resolution. For example, the date 1095767411000
+ * (which represents 2004-09-21 13:50:11) will be changed to
+ * 1093989600000 (2004-09-01 00:00:00) when using
+ * Resolution.MONTH.
+ *
+ * @param resolution The desired resolution of the date to be returned
+ * @return the date with all values more precise than resolution
+ * set to 0 or 1, expressed as milliseconds since January 1, 1970, 00:00:00 GMT
+ */
+ @SuppressWarnings("fallthrough")
+ public static long round(long time, Resolution resolution) {
+ final Calendar calInstance = TL_CAL.get();
+ calInstance.setTimeInMillis(time);
+
+ switch (resolution) {
+ //NOTE: switch statement fall-through is deliberate
+ case YEAR:
+ calInstance.set(Calendar.MONTH, 0);
+ case MONTH:
+ calInstance.set(Calendar.DAY_OF_MONTH, 1);
+ case DAY:
+ calInstance.set(Calendar.HOUR_OF_DAY, 0);
+ case HOUR:
+ calInstance.set(Calendar.MINUTE, 0);
+ case MINUTE:
+ calInstance.set(Calendar.SECOND, 0);
+ case SECOND:
+ calInstance.set(Calendar.MILLISECOND, 0);
+ case MILLISECOND:
+ // don't cut off anything
+ break;
+ default:
+ throw new IllegalArgumentException("unknown resolution " + resolution);
+ }
+ return calInstance.getTimeInMillis();
+ }
+
+ /** Specifies the time granularity. */
+ public static enum Resolution {
+
+ YEAR(4), MONTH(6), DAY(8), HOUR(10), MINUTE(12), SECOND(14), MILLISECOND(17);
+
+ final int formatLen;
+ final SimpleDateFormat format;//should be cloned before use, since it's not threadsafe
+
+ Resolution(int formatLen) {
+ this.formatLen = formatLen;
+ // formatLen 10's place: 11111111
+ // formatLen 1's place: 12345678901234567
+ this.format = new SimpleDateFormat("yyyyMMddHHmmssSSS".substring(0,formatLen),Locale.US);
+ this.format.setTimeZone(GMT);
+ }
+
+ /** this method returns the name of the resolution
+ * in lowercase (for backwards compatibility) */
+ @Override
+ public String toString() {
+ return super.toString().toLowerCase(Locale.ENGLISH);
+ }
+
+ }
+
+}