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     */
017    package org.apache.logging.log4j.core.util;
018    
019    import org.apache.logging.log4j.status.StatusLogger;
020    import org.apache.logging.log4j.util.PropertiesUtil;
021    
022    /**
023     * Factory for {@code Clock} objects.
024     */
025    public 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    }