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.security.AccessController;
020    import java.security.PrivilegedAction;
021    
022    /**
023     * <em>Consider this class private.</em> Utility class for ClassLoaders.
024     * @see ClassLoader
025     * @see Thread#getContextClassLoader()
026     */
027    // TODO: migrate any other useful methods from Loader in log4j-core
028    public final class LoaderUtil {
029        private LoaderUtil() {}
030    
031        private static final PrivilegedAction<ClassLoader> TCCL_GETTER = new ThreadContextClassLoaderGetter();
032    
033        static {
034            final SecurityManager sm = System.getSecurityManager();
035            if (sm != null) {
036                sm.checkPermission(new RuntimePermission("getClassLoader"));
037            }
038        }
039    
040        /**
041         * Gets the current Thread ClassLoader. Returns the system ClassLoader if the TCCL is {@code null}.
042         *
043         * @return the current ThreadContextClassLoader.
044         */
045        public static ClassLoader getThreadContextClassLoader() {
046            return System.getSecurityManager() == null
047                ? TCCL_GETTER.run()
048                : AccessController.doPrivileged(TCCL_GETTER);
049        }
050    
051        private static class ThreadContextClassLoaderGetter implements PrivilegedAction<ClassLoader> {
052            @Override
053            public ClassLoader run() {
054                final ClassLoader cl = Thread.currentThread().getContextClassLoader();
055                // if the TCCL is null, that means we're using the system CL
056                return cl == null ? ClassLoader.getSystemClassLoader() : cl;
057            }
058        }
059    }