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The source code

package org.apache.lucene.document;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

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.
 * 
 * 

* 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 yyyy-mm-dd hh:mm:ss * (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. * *

* 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)); } }

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