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.commons.discovery.jdk;
018    
019    import java.io.IOException;
020    import java.net.URL;
021    import java.util.Enumeration;
022    
023    /**
024     * JDK Hooks to extract properties/resources.
025     */
026    public abstract class JDKHooks {
027    
028        private static final JDKHooks jdkHooks;
029    
030        static {
031            jdkHooks = new JDK12Hooks();
032        }
033    
034        /**
035         * Hidden constructor, this class can't be directly instantiated.
036         */
037        protected JDKHooks() { }
038    
039        /**
040         * Return singleton object representing JVM hooks/tools.
041         *
042         * TODO: add logic to detect JDK level.
043         *
044         * @return The detected {@code JDKHooks}
045         */
046        public static final JDKHooks getJDKHooks() {
047            return jdkHooks;
048        }
049    
050        /**
051         * Get the system property
052         *
053         * @param propName name of the property
054         * @return value of the property
055         */
056        public abstract String getSystemProperty(final String propName);
057    
058        /**
059         * The thread context class loader is available for JDK 1.2
060         * or later, if certain security conditions are met.
061         *
062         * @return The thread context class loader, if available.
063         *         Otherwise return null.
064         */
065        public abstract ClassLoader getThreadContextClassLoader();
066    
067        /**
068         * The system class loader is available for JDK 1.2
069         * or later, if certain security conditions are met.
070         *
071         * @return The system class loader, if available.
072         *         Otherwise return null.
073         */
074        public abstract ClassLoader getSystemClassLoader();
075    
076        /**
077         * Resolve resource with given names and make them available in
078         * the returned iterator.
079         *
080         * @param loader The class loader used to resolve resources
081         * @param resourceName The resource name to resolve
082         * @return The iterator over the URL resolved resources
083         * @throws IOException if any error occurs while loading the resource
084         */
085        public abstract Enumeration<URL> getResources(ClassLoader loader, String resourceName) throws IOException;
086    
087    }