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 */
017package org.apache.commons.discovery.jdk;
018
019import java.io.IOException;
020import java.net.URL;
021import java.util.Enumeration;
022
023/**
024 * JDK Hooks to extract properties/resources.
025 */
026public 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}