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    }