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.xbean.classloader;
018
019import java.util.Enumeration;
020import java.util.Iterator;
021import java.util.Collection;
022import java.util.NoSuchElementException;
023
024/**
025 * @version $Rev: 437551 $ $Date: 2006-08-28 08:14:47 +0200 (lun. 28 ao?t 2006) $
026 */
027public class ResourceEnumeration implements Enumeration {
028    private Iterator iterator;
029    private final String resourceName;
030    private Object next;
031
032    public ResourceEnumeration(Collection resourceLocations, String resourceName) {
033        this.iterator = resourceLocations.iterator();
034        this.resourceName = resourceName;
035    }
036
037    public boolean hasMoreElements() {
038        fetchNext();
039        return (next != null);
040    }
041
042    public Object nextElement() {
043        fetchNext();
044
045        // save next into a local variable and clear the next field
046        Object next = this.next;
047        this.next = null;
048
049        // if we didn't have a next throw an exception
050        if (next == null) {
051            throw new NoSuchElementException();
052        }
053        return next;
054    }
055
056    private void fetchNext() {
057        if (iterator == null) {
058            return;
059        }
060        if (next != null) {
061            return;
062        }
063
064        try {
065            while (iterator.hasNext()) {
066                ResourceLocation resourceLocation = (ResourceLocation) iterator.next();
067                ResourceHandle resourceHandle = resourceLocation.getResourceHandle(resourceName);
068                if (resourceHandle != null) {
069                    next = resourceHandle.getUrl();
070                    return;
071                }
072            }
073            // no more elements
074            // clear the iterator so it can be GCed
075            iterator = null;
076        } catch (IllegalStateException e) {
077            // Jar file was closed... this means the resource finder was destroyed
078            // clear the iterator so it can be GCed
079            iterator = null;
080            throw e;
081        }
082    }
083}