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.ArrayList;
022    import java.util.Collection;
023    import java.util.Enumeration;
024    import java.util.Properties;
025    
026    import org.apache.logging.log4j.Logger;
027    import org.apache.logging.log4j.spi.Provider;
028    import org.apache.logging.log4j.status.StatusLogger;
029    
030    /**
031     * <em>Consider this class private.</em>
032     */
033    public final class ProviderUtil {
034    
035        private static final String PROVIDER_RESOURCE = "META-INF/log4j-provider.properties";
036        private static final String API_VERSION = "Log4jAPIVersion";
037    
038        private static final String[] COMPATIBLE_API_VERSIONS = {
039            "2.0.0"
040        };
041    
042        private static final Logger LOGGER = StatusLogger.getLogger();
043    
044        private static final Collection<Provider> PROVIDERS = new ArrayList<Provider>();
045    
046        private ProviderUtil() {
047        }
048    
049        static {
050            final ClassLoader cl = findClassLoader();
051            Enumeration<URL> enumResources = null;
052            try {
053                enumResources = cl.getResources(PROVIDER_RESOURCE);
054            } catch (final IOException e) {
055                LOGGER.fatal("Unable to locate {}", PROVIDER_RESOURCE, e);
056            }
057            loadProviders(enumResources);
058        }
059    
060        protected static void loadProviders(final Enumeration<URL> enumResources) {
061            if (enumResources != null) {
062                while (enumResources.hasMoreElements()) {
063                    final URL url = enumResources.nextElement();
064                    try {
065                        final Properties props = PropertiesUtil.loadClose(url.openStream(), url);
066                        if (!validVersion(props.getProperty(API_VERSION))) {
067                            continue;
068                        }
069                        PROVIDERS.add(new Provider(props, url));
070                    } catch (final IOException ioe) {
071                        LOGGER.error("Unable to open {}", url, ioe);
072                    }
073                }
074            }
075        }
076    
077        public static Iterable<Provider> getProviders() {
078            return PROVIDERS;
079        }
080    
081        public static boolean hasProviders() {
082            return !PROVIDERS.isEmpty();
083        }
084    
085        public static ClassLoader findClassLoader() {
086            ClassLoader cl;
087            if (System.getSecurityManager() == null) {
088                cl = Thread.currentThread().getContextClassLoader();
089            } else {
090                cl = java.security.AccessController.doPrivileged(
091                    new java.security.PrivilegedAction<ClassLoader>() {
092                        @Override
093                        public ClassLoader run() {
094                            return Thread.currentThread().getContextClassLoader();
095                        }
096                    }
097                );
098            }
099            if (cl == null) {
100                cl = ProviderUtil.class.getClassLoader();
101            }
102    
103            return cl;
104        }
105    
106        private static boolean validVersion(final String version) {
107            for (final String v : COMPATIBLE_API_VERSIONS) {
108                if (version.startsWith(v)) {
109                    return true;
110                }
111            }
112            return false;
113        }
114    }