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 parent aware url stream handler factory delegates to a parent
024     * url stream handler factory,
025     */
026    public abstract class ParentAwareURLStreamHandlerFactory implements URLStreamHandlerFactory {
027    
028        protected URLStreamHandlerFactory parentFactory;
029    
030        /**
031         * Set the parent factory.
032         * @param factory
033         */
034        public void setParentFactory(URLStreamHandlerFactory factory) {
035            this.parentFactory = factory;
036        }
037    
038        /**
039         * Return the parent factory.
040         * @return The parent factory.
041         */
042        public URLStreamHandlerFactory getParent() {
043            return this.parentFactory;
044        }
045    
046        /**
047         * @see java.net.URLStreamHandlerFactory#createURLStreamHandler(java.lang.String)
048         */
049        public URLStreamHandler createURLStreamHandler(String protocol) {
050            URLStreamHandler handler = this.create(protocol);
051            if ( handler == null && this.parentFactory != null ) {
052                handler = this.parentFactory.createURLStreamHandler(protocol);
053            }
054            return handler;
055        }
056    
057        /**
058         * This method can be overwritten by subclasses to instantiate url stream
059         * handlers for the given protocol.
060         * @param protocol The protocol.
061         * @return A url stream handler for the protocol or null.
062         */
063        protected abstract URLStreamHandler create(String protocol);
064    }