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.jnet;
018    
019    import java.net.URLStreamHandler;
020    import java.net.URLStreamHandlerFactory;
021    
022    /**
023     * A dynamic url stream handler factory that stores the current delegate factory
024     * in a thread local variable.
025     *
026     * This allows to change the url handler factory at runtime dynamically through
027     * the {@link #push(URLStreamHandlerFactory)} and {@link #pop()} methods.
028     */
029    public class DynamicURLStreamHandlerFactory extends ParentAwareURLStreamHandlerFactory {
030    
031        /** The thread local holding the current factory. */
032        protected static final ThreadLocal FACTORY = new InheritableThreadLocal();
033    
034        /**
035         * Push a url stream handler factory on top of the stack.
036         */
037        public static void push(URLStreamHandlerFactory factory) {
038            // no need to synchronize as we use a thread local
039            if ( !(factory instanceof ParentAwareURLStreamHandlerFactory) ) {
040                factory = new URLStreamHandlerFactoryWrapper(factory);
041            }
042            URLStreamHandlerFactory old = (URLStreamHandlerFactory) FACTORY.get();
043            ((ParentAwareURLStreamHandlerFactory)factory).setParentFactory(old);
044            FACTORY.set(factory);
045        }
046    
047        /**
048         * Pop the lastest url stream handler factory from the stack.
049         */
050        public static void pop() {
051            ParentAwareURLStreamHandlerFactory factory = (ParentAwareURLStreamHandlerFactory)FACTORY.get();
052            if ( factory != null ) {
053                FACTORY.set(factory.getParent());
054            }
055        }
056    
057        /**
058         * @see org.apache.commons.jnet.ParentAwareURLStreamHandlerFactory#create(java.lang.String)
059         */
060        protected URLStreamHandler create(String protocol) {
061            ParentAwareURLStreamHandlerFactory factory = (ParentAwareURLStreamHandlerFactory)FACTORY.get();
062            if ( factory != null ) {
063                return factory.createURLStreamHandler(protocol);
064            }
065            return null;
066        }
067    }