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.resource.names;
018    
019    import java.util.Vector;
020    
021    import org.apache.commons.discovery.ResourceNameDiscover;
022    import org.apache.commons.discovery.ResourceNameIterator;
023    import org.apache.commons.discovery.log.DiscoveryLogFactory;
024    import org.apache.commons.logging.Log;
025    
026    
027    /**
028     * Holder for multiple ResourceNameDiscover instances.
029     * The result is the union of the results from each
030     * (not a chained sequence, where results feed the next in line.
031     *
032     * @author Richard A. Sitze
033     */
034    public class NameDiscoverers
035        extends ResourceNameDiscoverImpl
036        implements ResourceNameDiscover
037    {
038        private static Log log = DiscoveryLogFactory.newLog(NameDiscoverers.class);
039        public static void setLog(Log _log) {
040            log = _log;
041        }
042    
043        private Vector discoverers = new Vector();
044        
045        /**
046         *  Construct a new resource name discoverer
047         */
048        public NameDiscoverers() {
049        }
050        
051        /**
052         * Specify an additional class loader to be used in searching.
053         * The order of loaders determines the order of the result.
054         * It is recommended to add the most specific loaders first.
055         */
056        public void addResourceNameDiscover(ResourceNameDiscover discover) {
057            if (discover != null) {
058                discoverers.addElement(discover);
059            }
060        }
061    
062        protected ResourceNameDiscover getResourceNameDiscover(int idx) {
063            return (ResourceNameDiscover)discoverers.get(idx);
064        }
065    
066        protected int size() {
067            return discoverers.size();
068        }
069    
070        /**
071         * Set of results of all discoverers.
072         * 
073         * @return ResourceIterator
074         */
075        public ResourceNameIterator findResourceNames(final String resourceName) {
076            if (log.isDebugEnabled())
077                log.debug("find: resourceName='" + resourceName + "'");
078    
079            return new ResourceNameIterator() {
080                private int idx = 0;
081                private ResourceNameIterator iterator = null;
082                
083                public boolean hasNext() {
084                    if (iterator == null  ||  !iterator.hasNext()) {
085                        iterator = getNextIterator();
086                        if (iterator == null) {
087                            return false;
088                        }
089                    }
090                    return iterator.hasNext();
091                }
092                
093                public String nextResourceName() {
094                    return iterator.nextResourceName();
095                }
096                
097                private ResourceNameIterator getNextIterator() {
098                    while (idx < size()) {
099                        ResourceNameIterator iter =
100                            getResourceNameDiscover(idx++).findResourceNames(resourceName);
101    
102                        if (iter.hasNext()) {
103                            return iter;
104                        }
105                    }
106                    return null;
107                }
108            };
109        }
110    }