001    // Copyright 2009, 2011 The Apache Software Foundation
002    //
003    // Licensed under the Apache License, Version 2.0 (the "License");
004    // you may not use this file except in compliance with the License.
005    // You may obtain a copy of the License at
006    //
007    //     http://www.apache.org/licenses/LICENSE-2.0
008    //
009    // Unless required by applicable law or agreed to in writing, software
010    // distributed under the License is distributed on an "AS IS" BASIS,
011    // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
012    // See the License for the specific language governing permissions and
013    // limitations under the License.
014    
015    package org.apache.tapestry5.ioc.internal.util;
016    
017    import java.util.concurrent.locks.Lock;
018    import java.util.concurrent.locks.ReentrantLock;
019    
020    /**
021     * Internal utilities for identifying the JDK version, used in the rare cases
022     * that we are patching around JDK bugs.
023     */
024    public class JDKUtils
025    {
026        /**
027         * Is the running JVM JDK 1.5?
028         */
029        public static final boolean JDK_1_5 = isVersion("1.5");
030    
031        private static boolean isVersion(String versionId)
032        {
033            return System.getProperty("java.specification.version").equals(versionId);
034        }
035    
036        /**
037         * Returns a {@link ReentrantLock} used to serialize access to the construction of a thread local; this is only needed under JDK 1.5 (due to a bug in the JDK);
038         * for other JDKs, a {@link DummyLock} is returned.
039         *
040         * @return lock to use when creating
041         * @since 5.3
042         */
043        public static Lock createLockForThreadLocalCreation()
044        {
045            return JDK_1_5 ? new ReentrantLock() : new DummyLock();
046        }
047    }