001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements. See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache license, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License. You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the license for the specific language governing permissions and
015 * limitations under the license.
016 */
017package org.apache.logging.log4j.core.util;
018
019import org.apache.logging.log4j.status.StatusLogger;
020import org.apache.logging.log4j.util.PropertiesUtil;
021
022/**
023 * Factory for {@code Clock} objects.
024 */
025public final class ClockFactory {
026
027    /**
028     * Name of the system property that can be used to specify a {@code Clock}
029     * implementation class. The value of this property is {@value}.
030     */
031    public static final String PROPERTY_NAME = "log4j.Clock";
032    private static final StatusLogger LOGGER = StatusLogger.getLogger();
033
034    // private static final Clock clock = createClock();
035
036    private ClockFactory() {
037    }
038
039    /**
040     * Returns a {@code Clock} instance depending on the value of system
041     * property {@link #PROPERTY_NAME}.
042     * <p>
043     * If system property {@code log4j.Clock=CachedClock} is specified,
044     * this method returns an instance of {@link CachedClock}. If system
045     * property {@code log4j.Clock=CoarseCachedClock} is specified, this
046     * method returns an instance of {@link CoarseCachedClock}.
047     * </p>
048     * <p>
049     * If another value is specified, this value is taken as the fully qualified
050     * class name of a class that implements the {@code Clock} interface. An
051     * object of this class is instantiated and returned.
052     * </p>
053     * <p>
054     * If no value is specified, or if the specified value could not correctly
055     * be instantiated or did not implement the {@code Clock} interface, then an
056     * instance of {@link SystemClock} is returned.
057     * </p>
058     *
059     * @return a {@code Clock} instance
060     */
061    public static Clock getClock() {
062        return createClock();
063    }
064
065    private static Clock createClock() {
066        final String userRequest = PropertiesUtil.getProperties().getStringProperty(PROPERTY_NAME);
067        if (userRequest == null || "SystemClock".equals(userRequest)) {
068            LOGGER.debug("Using default SystemClock for timestamps");
069            return new SystemClock();
070        }
071        if (CachedClock.class.getName().equals(userRequest)
072                || "CachedClock".equals(userRequest)) {
073            LOGGER.debug("Using specified CachedClock for timestamps");
074            return CachedClock.instance();
075        }
076        if (CoarseCachedClock.class.getName().equals(userRequest)
077                || "CoarseCachedClock".equals(userRequest)) {
078            LOGGER.debug("Using specified CoarseCachedClock for timestamps");
079            return CoarseCachedClock.instance();
080        }
081        try {
082            final Clock result = Loader.newCheckedInstanceOf(userRequest, Clock.class);
083            LOGGER.debug("Using {} for timestamps", result.getClass().getName());
084            return result;
085        } catch (final Exception e) {
086            final String fmt = "Could not create {}: {}, using default SystemClock for timestamps";
087            LOGGER.error(fmt, userRequest, e);
088            return new SystemClock();
089        }
090    }
091}