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.core.time.PreciseClock;
020import org.apache.logging.log4j.status.StatusLogger;
021import org.apache.logging.log4j.util.PropertiesUtil;
022import org.apache.logging.log4j.util.Supplier;
023
024import java.util.HashMap;
025import java.util.Map;
026
027/**
028 * Factory for {@code Clock} objects.
029 */
030public final class ClockFactory {
031
032    /**
033     * Name of the system property that can be used to specify a {@code Clock}
034     * implementation class. The value of this property is {@value}.
035     */
036    public static final String PROPERTY_NAME = "log4j.Clock";
037    private static final StatusLogger LOGGER = StatusLogger.getLogger();
038
039    // private static final Clock clock = createClock();
040
041    private ClockFactory() {
042    }
043
044    /**
045     * Returns a {@code Clock} instance depending on the value of system
046     * property {@link #PROPERTY_NAME}.
047     * <p>
048     * If system property {@code log4j.Clock=CachedClock} is specified,
049     * this method returns an instance of {@link CachedClock}. If system
050     * property {@code log4j.Clock=CoarseCachedClock} is specified, this
051     * method returns an instance of {@link CoarseCachedClock}.
052     * </p>
053     * <p>
054     * If another value is specified, this value is taken as the fully qualified
055     * class name of a class that implements the {@code Clock} interface. An
056     * object of this class is instantiated and returned.
057     * </p>
058     * <p>
059     * If no value is specified, or if the specified value could not correctly
060     * be instantiated or did not implement the {@code Clock} interface, then an
061     * instance of {@link SystemClock} is returned.
062     * </p>
063     *
064     * @return a {@code Clock} instance
065     */
066    public static Clock getClock() {
067        return createClock();
068    }
069
070    private static Map<String, Supplier<Clock>> aliases() {
071        final Map<String, Supplier<Clock>> result = new HashMap<>();
072        result.put("SystemClock",       SystemClock::new);
073        result.put("SystemMillisClock", SystemMillisClock::new);
074        result.put("CachedClock",       CachedClock::instance);
075        result.put("CoarseCachedClock", CoarseCachedClock::instance);
076        result.put("org.apache.logging.log4j.core.util.CachedClock", CachedClock::instance);
077        result.put("org.apache.logging.log4j.core.util.CoarseCachedClock", CoarseCachedClock::instance);
078        return result;
079    }
080
081    private static Clock createClock() {
082        final String userRequest = PropertiesUtil.getProperties().getStringProperty(PROPERTY_NAME);
083        if (userRequest == null) {
084            LOGGER.trace("Using default SystemClock for timestamps.");
085            return logSupportedPrecision(new SystemClock());
086        }
087        final Supplier<Clock> specified = aliases().get(userRequest);
088        if (specified != null) {
089            LOGGER.trace("Using specified {} for timestamps.", userRequest);
090            return logSupportedPrecision(specified.get());
091        }
092        try {
093            final Clock result = Loader.newCheckedInstanceOf(userRequest, Clock.class);
094            LOGGER.trace("Using {} for timestamps.", result.getClass().getName());
095            return logSupportedPrecision(result);
096        } catch (final Exception e) {
097            final String fmt = "Could not create {}: {}, using default SystemClock for timestamps.";
098            LOGGER.error(fmt, userRequest, e);
099            return logSupportedPrecision(new SystemClock());
100        }
101    }
102
103    private static Clock logSupportedPrecision(final Clock clock) {
104        final String support = clock instanceof PreciseClock ? "supports" : "does not support";
105        LOGGER.debug("{} {} precise timestamps.", clock.getClass().getName(), support);
106        return clock;
107    }
108}