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;
018    
019    import org.apache.commons.discovery.Resource;
020    import org.apache.commons.discovery.ResourceDiscover;
021    import org.apache.commons.discovery.ResourceIterator;
022    import org.apache.commons.discovery.ResourceNameIterator;
023    import org.apache.commons.discovery.resource.names.ResourceNameDiscoverImpl;
024    
025    
026    /**
027     * Helper class for methods implementing the ResourceDiscover interface.
028     * 
029     * @author Richard A. Sitze
030     */
031    public abstract class ResourceDiscoverImpl
032        extends ResourceNameDiscoverImpl
033        implements ResourceDiscover
034    {
035        private ClassLoaders classLoaders;
036    
037        
038        /**
039         * Construct a new resource discoverer
040         */
041        public ResourceDiscoverImpl() {
042        }
043        
044        /**
045         *  Construct a new resource discoverer
046         */
047        public ResourceDiscoverImpl(ClassLoaders classLoaders) {
048            setClassLoaders(classLoaders);
049        }
050    
051        /**
052         * Specify set of class loaders to be used in searching.
053         */
054        public void setClassLoaders(ClassLoaders loaders) {
055            classLoaders = loaders;
056        }
057    
058        /**
059         * Specify a new class loader to be used in searching.
060         * The order of loaders determines the order of the result.
061         * It is recommended to add the most specific loaders first.
062         */
063        public void addClassLoader(ClassLoader loader) {
064            getClassLoaders().put(loader);
065        }
066    
067        protected ClassLoaders getClassLoaders() {
068            if (classLoaders == null) {
069                classLoaders = ClassLoaders.getLibLoaders(this.getClass(), null, true);
070            }
071            return classLoaders;
072        }
073    
074        /**
075         * Locate names of resources that are bound to <code>resourceName</code>.
076         * 
077         * @return ResourceNameIterator
078         */
079        public ResourceNameIterator findResourceNames(String resourceName) {
080            return findResources(resourceName);
081        }
082    
083        /**
084         * Locate names of resources that are bound to <code>resourceNames</code>.
085         * 
086         * @return ResourceNameIterator
087         */
088        public ResourceNameIterator findResourceNames(ResourceNameIterator resourceNames) {
089            return findResources(resourceNames);
090        }
091    
092        /**
093         * Locate resources that are bound to <code>resourceName</code>.
094         * 
095         * @return ResourceIterator
096         */
097        public abstract ResourceIterator findResources(String resourceName);
098    
099        /**
100         * Locate resources that are bound to <code>resourceNames</code>.
101         * 
102         * @return ResourceIterator
103         */
104        public ResourceIterator findResources(final ResourceNameIterator inputNames) {
105            return new ResourceIterator() {
106                private ResourceIterator resources = null;
107                private Resource resource = null;
108                
109                public boolean hasNext() {
110                    if (resource == null) {
111                        resource = getNextResource();
112                    }
113                    return resource != null;
114                }
115                
116                public Resource nextResource() {
117                    Resource rsrc = resource;
118                    resource = null;
119                    return rsrc;
120                }
121                
122                private Resource getNextResource() {
123                    while (inputNames.hasNext() &&
124                           (resources == null  ||  !resources.hasNext())) {
125                        resources = findResources(inputNames.nextResourceName());
126                    }
127        
128                    return (resources != null  &&  resources.hasNext())
129                           ? resources.nextResource()
130                           : null;
131                }
132            };
133        }
134    }