DateField.java :  » Search-Engine » snapper » org » enhydra » snapper » wrapper » lucene » Java Open Source

package org.enhydra.snapper.wrapper.lucene;

/**

 */

import java.util.Date;

/**
 * Provides support for converting dates to strings and vice-versa.
 * The strings are structured so that lexicographic sorting orders by date,
 * which makes them suitable for use as field values and search terms.
 * 
 * <P>
 * Note that you do not have to use this class, you can just save your
 * dates as strings if lexicographic sorting orders them by date. This is
 * the case for example for dates like <code>yyyy-mm-dd hh:mm:ss</code>
 * (of course you can leave out the delimiter characters to save some space).
 * The advantage with using such a format is that you can easily save dates
 * with the required granularity, e.g. leaving out seconds. This saves memory
 * when searching with a RangeQuery or PrefixQuery, as Lucene
 * expands these queries to a BooleanQuery with potentially very many terms. 
 * 
 * <P>
 * Note: dates before 1970 cannot be used, and therefore cannot be
 * indexed when using this class.
 */
public class DateField {
  private DateField() {}

  // make date strings long enough to last a millenium
  private static int DATE_LEN = Long.toString(1000L*365*24*60*60*1000,
                 Character.MAX_RADIX).length();

  public static String MIN_DATE_STRING() {
    return timeToString(0);
  }

  public static String MAX_DATE_STRING() {
    char[] buffer = new char[DATE_LEN];
    char c = Character.forDigit(Character.MAX_RADIX-1, Character.MAX_RADIX);
    for (int i = 0 ; i < DATE_LEN; i++)
      buffer[i] = c;
    return new String(buffer);
  }

  /**
   * Converts a Date to a string suitable for indexing.
   * @throws RuntimeException if the date specified in the
   * method argument is before 1970
   */
  public static String dateToString(Date date) {
    return timeToString(date.getTime());
  }
  /**
   * Converts a millisecond time to a string suitable for indexing.
   * @throws RuntimeException if the time specified in the
   * method argument is negative, that is, before 1970
   */
  public static String timeToString(long time) {
    if (time < 0)
      throw new RuntimeException("time too early");

    String s = Long.toString(time, Character.MAX_RADIX);

    if (s.length() > DATE_LEN)
      throw new RuntimeException("time too late");

    // Pad with leading zeros
    if (s.length() < DATE_LEN) {
      StringBuffer sb = new StringBuffer(s);
      while (sb.length() < DATE_LEN)
        sb.insert(0, 0);
      s = sb.toString();
    }

    return s;
  }

  /** Converts a string-encoded date into a millisecond time. */
  public static long stringToTime(String s) {
    return Long.parseLong(s, Character.MAX_RADIX);
  }
  /** Converts a string-encoded date into a Date object. */
  public static Date stringToDate(String s) {
    return new Date(stringToTime(s));
  }
}