    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.util;
    018
    019    import java.io.IOException;
    020    import java.net.URL;
    021    import java.util.Collection;
    022    import java.util.Enumeration;
    023    import java.util.HashSet;
    024    import java.util.Properties;
    025    import java.util.concurrent.locks.Lock;
    026    import java.util.concurrent.locks.ReentrantLock;
    027
    028    import org.apache.logging.log4j.Logger;
    029    import org.apache.logging.log4j.spi.Provider;
    030    import org.apache.logging.log4j.status.StatusLogger;
    031
    032    /**
    033     * <em>Consider this class private.</em>
    034     * Utility class for Log4j {@link Provider}s. When integrating with an application container framework, any Log4j
    035     * Providers not accessible through standard classpath scanning should {@link #loadProvider(java.net.URL, ClassLoader)}
    036     * a classpath accordingly.
    037     */
    038    public final class ProviderUtil {
    039
    040        /**
    041         * Resource name for a Log4j 2 provider properties file.
    042         */
    043        protected static final String PROVIDER_RESOURCE = "META-INF/log4j-provider.properties";
    044        private static final String API_VERSION = "Log4jAPIVersion";
    045
    046        private static final String[] COMPATIBLE_API_VERSIONS = {
    047            "2.0.0", "2.1.0"
    048        };
    049
    050        private static final Logger LOGGER = StatusLogger.getLogger();
    051
    052        protected static final Collection<Provider> PROVIDERS = new HashSet<Provider>();
    053
    054        /**
    055         * Guards the ProviderUtil singleton instance from lazy initialization. This is primarily used for OSGi support.
    056         *
    057         * @since 2.1
    058         */
    059        protected static final Lock STARTUP_LOCK = new ReentrantLock();
    060        // STARTUP_LOCK guards INSTANCE for lazy initialization; this allows the OSGi Activator to pause the startup and
    061        // wait for a Provider to be installed. See LOG4J2-373
    062        private static volatile ProviderUtil INSTANCE;
    063
    064        private ProviderUtil() {
    065            for (final LoaderUtil.UrlResource resource : LoaderUtil.findUrlResources(PROVIDER_RESOURCE)) {
    066                loadProvider(resource.getUrl(), resource.getClassLoader());
    067            }
    068        }
    069
    070        /**
    071         * Loads an individual Provider implementation. This method is really only useful for the OSGi bundle activator
    072         * and this class itself.
    073         *
    074         * @param url the URL to the provider properties file
    075         * @param cl the ClassLoader to load the provider classes with
    076         */
    077        protected static void loadProvider(final URL url, final ClassLoader cl) {
    078            try {
    079                final Properties props = PropertiesUtil.loadClose(url.openStream(), url);
    080                if (validVersion(props.getProperty(API_VERSION))) {
    081                    PROVIDERS.add(new Provider(props, url, cl));
    082                }
    083            } catch (final IOException e) {
    084                LOGGER.error("Unable to open {}", url, e);
    085            }
    086        }
    087
    088        /**
    089         * @deprecated Use {@link #loadProvider(java.net.URL, ClassLoader)} instead. Will be removed in 3.0.
    090         */
    091        @Deprecated
    092        protected static void loadProviders(final Enumeration<URL> urls, final ClassLoader cl) {
    093            if (urls != null) {
    094                while (urls.hasMoreElements()) {
    095                    loadProvider(urls.nextElement(), cl);
    096                }
    097            }
    098        }
    099
    100        public static Iterable<Provider> getProviders() {
    101            lazyInit();
    102            return PROVIDERS;
    103        }
    104
    105        public static boolean hasProviders() {
    106            lazyInit();
    107            return !PROVIDERS.isEmpty();
    108        }
    109
    110        /**
    111         * Lazily initializes the ProviderUtil singleton.
    112         *
    113         * @since 2.1
    114         */
    115        protected static void lazyInit() {
    116            //noinspection DoubleCheckedLocking
    117            if (INSTANCE == null) {
    118                try {
    119                    STARTUP_LOCK.lockInterruptibly();
    120                    try {
    121                        if (INSTANCE == null) {
    122                            INSTANCE = new ProviderUtil();
    123                        }
    124                    } finally {
    125                        STARTUP_LOCK.unlock();
    126                    }
    127                } catch (final InterruptedException e) {
    128                    LOGGER.fatal("Interrupted before Log4j Providers could be loaded.", e);
    129                    Thread.currentThread().interrupt();
    130                }
    131            }
    132        }
    133
    134        public static ClassLoader findClassLoader() {
    135            return LoaderUtil.getThreadContextClassLoader();
    136        }
    137
    138        private static boolean validVersion(final String version) {
    139            for (final String v : COMPATIBLE_API_VERSIONS) {
    140                if (version.startsWith(v)) {
    141                    return true;
    142                }
    143            }
    144            return false;
    145        }
    146    }