001/*
002 * Copyright (C) 2014 Jörg Prante
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 *      http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016package org.xbib.elasticsearch.plugin.jdbc.classloader;
017
018import java.net.URL;
019import java.util.Collection;
020import java.util.Enumeration;
021import java.util.Iterator;
022import java.util.NoSuchElementException;
023
024public class ResourceEnumeration implements Enumeration<URL> {
025
026    private Iterator iterator;
027
028    private final String resourceName;
029
030    private URL 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 URL nextElement() {
043        fetchNext();
044        // save next into a local variable and clear the next field
045        URL next = this.next;
046        this.next = null;
047        // if we didn't have a next throw an exception
048        if (next == null) {
049            throw new NoSuchElementException();
050        }
051        return next;
052    }
053
054    private void fetchNext() {
055        if (iterator == null) {
056            return;
057        }
058        if (next != null) {
059            return;
060        }
061        try {
062            while (iterator.hasNext()) {
063                ResourceLocation resourceLocation = (ResourceLocation) iterator.next();
064                ResourceHandle resourceHandle = resourceLocation.getResourceHandle(resourceName);
065                if (resourceHandle != null) {
066                    next = resourceHandle.getUrl();
067                    return;
068                }
069            }
070            // no more elements
071            // clear the iterator so it can be GCed
072            iterator = null;
073        } catch (IllegalStateException e) {
074            // Jar file was closed... this means the resource finder was destroyed
075            // clear the iterator so it can be GCed
076            iterator = null;
077            throw e;
078        }
079    }
080}