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 }