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.util; 018 019import java.io.IOException; 020import java.net.URL; 021import java.util.Collection; 022import java.util.Enumeration; 023import java.util.HashSet; 024import java.util.Properties; 025import java.util.concurrent.locks.Lock; 026import java.util.concurrent.locks.ReentrantLock; 027 028import org.apache.logging.log4j.Logger; 029import org.apache.logging.log4j.spi.Provider; 030import 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 */ 038public 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}