001/*
002 * Copyright (c) 2010-2024 Mark Allen, Norbert Bartels.
003 *
004 * Permission is hereby granted, free of charge, to any person obtaining a copy
005 * of this software and associated documentation files (the "Software"), to deal
006 * in the Software without restriction, including without limitation the rights
007 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
008 * copies of the Software, and to permit persons to whom the Software is
009 * furnished to do so, subject to the following conditions:
010 *
011 * The above copyright notice and this permission notice shall be included in
012 * all copies or substantial portions of the Software.
013 *
014 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
015 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
016 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
017 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
018 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
019 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
020 * THE SOFTWARE.
021 */
022package com.restfb.util;
023
024import java.lang.ref.SoftReference;
025import java.text.DateFormat;
026import java.text.SimpleDateFormat;
027import java.util.HashMap;
028import java.util.Map;
029import java.util.TimeZone;
030
031/**
032 * a DateFormat strategy that returns a cached SimpleDateFormat instance.
033 * <p>
034 * For every format string an instance of the SimpleDateFormat is saved on a per thread base, so the SimpleDateFormat
035 * instance is reused and you get an major speedup.
036 * <p>
037 * Attention: to prevent a possible memory leak while using this strategy you have to clean up the inner ThreadLocal
038 * with the {@code clearThreadLocal} method.
039 * 
040 * @since 1.7.0
041 */
042public class CachedDateFormatStrategy implements DateFormatStrategy {
043
044  @Override
045  public DateFormat formatFor(String format) {
046    return SimpleDateFormatHolder.formatFor(format);
047  }
048
049  public void clearThreadLocal() {
050    SimpleDateFormatHolder.clearThreadLocal();
051  }
052
053  private static final class SimpleDateFormatHolder {
054
055    private static final ThreadLocal<SoftReference<Map<String, SimpleDateFormat>>> THREADLOCAL_FORMATTER_MAP =
056        ThreadLocal.withInitial(() -> new SoftReference<>(new HashMap<>()));
057
058    private static SimpleDateFormat formatFor(String pattern) {
059      SoftReference<Map<String, SimpleDateFormat>> ref = THREADLOCAL_FORMATTER_MAP.get();
060      Map<String, SimpleDateFormat> formatterMap = ref.get();
061      return formatterMap.computeIfAbsent(pattern, SimpleDateFormatHolder::createSDF);
062    }
063
064    private static SimpleDateFormat createSDF(String pattern) {
065      SimpleDateFormat sdf = new SimpleDateFormat(pattern);
066      sdf.setTimeZone(TimeZone.getTimeZone("UTC"));
067      return sdf;
068    }
069
070    private static void clearThreadLocal() {
071      THREADLOCAL_FORMATTER_MAP.remove();
072    }
073  }
074
075}