org.apache.logging.log4j.util.ProviderUtil Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache license, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the license for the specific language governing permissions and
* limitations under the license.
*/
package org.apache.logging.log4j.util;
import java.io.IOException;
import java.net.URL;
import java.util.Collection;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Properties;
import java.util.ServiceLoader;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.spi.Provider;
import org.apache.logging.log4j.status.StatusLogger;
/**
* Consider this class private. Utility class for Log4j {@link Provider}s. When integrating with an application
* container framework, any Log4j Providers not accessible through standard classpath scanning should
* {@link #loadProvider(java.net.URL, ClassLoader)} a classpath accordingly.
*/
public final class ProviderUtil {
/**
* Resource name for a Log4j 2 provider properties file.
*/
protected static final String PROVIDER_RESOURCE = "META-INF/log4j-provider.properties";
/**
* Loaded providers.
*/
protected static final Collection PROVIDERS = new HashSet<>();
/**
* Guards the ProviderUtil singleton instance from lazy initialization. This is primarily used for OSGi support.
*
* @since 2.1
*/
protected static final Lock STARTUP_LOCK = new ReentrantLock();
private static final String API_VERSION = "Log4jAPIVersion";
private static final String[] COMPATIBLE_API_VERSIONS = {"2.6.0"};
private static final Logger LOGGER = StatusLogger.getLogger();
// STARTUP_LOCK guards INSTANCE for lazy initialization; this allows the OSGi Activator to pause the startup and
// wait for a Provider to be installed. See LOG4J2-373
private static volatile ProviderUtil instance;
private ProviderUtil() {
for (final ClassLoader classLoader : LoaderUtil.getClassLoaders()) {
try {
loadProviders(classLoader);
} catch (final Throwable ex) {
LOGGER.debug("Unable to retrieve provider from ClassLoader {}", classLoader, ex);
}
}
for (final LoaderUtil.UrlResource resource : LoaderUtil.findUrlResources(PROVIDER_RESOURCE)) {
loadProvider(resource.getUrl(), resource.getClassLoader());
}
}
protected static void addProvider(final Provider provider) {
PROVIDERS.add(provider);
LOGGER.debug("Loaded Provider {}", provider);
}
/**
* Loads an individual Provider implementation. This method is really only useful for the OSGi bundle activator and
* this class itself.
*
* @param url the URL to the provider properties file
* @param cl the ClassLoader to load the provider classes with
*/
protected static void loadProvider(final URL url, final ClassLoader cl) {
try {
final Properties props = PropertiesUtil.loadClose(url.openStream(), url);
if (validVersion(props.getProperty(API_VERSION))) {
final Provider provider = new Provider(props, url, cl);
PROVIDERS.add(provider);
LOGGER.debug("Loaded Provider {}", provider);
}
} catch (final IOException e) {
LOGGER.error("Unable to open {}", url, e);
}
}
/**
*
* @param classLoader null can be used to mark the bootstrap class loader.
*/
protected static void loadProviders(final ClassLoader classLoader) {
final ServiceLoader serviceLoader = ServiceLoader.load(Provider.class, classLoader);
for (final Provider provider : serviceLoader) {
if (validVersion(provider.getVersions()) && !PROVIDERS.contains(provider)) {
PROVIDERS.add(provider);
}
}
}
/**
* @deprecated Use {@link #loadProvider(java.net.URL, ClassLoader)} instead. Will be removed in 3.0.
*/
@Deprecated
protected static void loadProviders(final Enumeration urls, final ClassLoader cl) {
if (urls != null) {
while (urls.hasMoreElements()) {
loadProvider(urls.nextElement(), cl);
}
}
}
public static Iterable getProviders() {
lazyInit();
return PROVIDERS;
}
public static boolean hasProviders() {
lazyInit();
return !PROVIDERS.isEmpty();
}
/**
* Lazily initializes the ProviderUtil singleton.
*
* @since 2.1
*/
protected static void lazyInit() {
// noinspection DoubleCheckedLocking
if (instance == null) {
try {
STARTUP_LOCK.lockInterruptibly();
try {
if (instance == null) {
instance = new ProviderUtil();
}
} finally {
STARTUP_LOCK.unlock();
}
} catch (final InterruptedException e) {
LOGGER.fatal("Interrupted before Log4j Providers could be loaded.", e);
Thread.currentThread().interrupt();
}
}
}
public static ClassLoader findClassLoader() {
return LoaderUtil.getThreadContextClassLoader();
}
private static boolean validVersion(final String version) {
for (final String v : COMPATIBLE_API_VERSIONS) {
if (version.startsWith(v)) {
return true;
}
}
return false;
}
}