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/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.xbean.classloader;

import java.net.URL;
import java.util.Collection;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * @author Dain Sundstrom
 */
public class ResourceEnumeration implements Enumeration {

	private Iterator iterator;
	private final String resourceName;
	private URL next;

	public ResourceEnumeration(Collection resourceLocations, String resourceName) {
		this.iterator = resourceLocations.iterator();
		this.resourceName = resourceName;
	}

	public boolean hasMoreElements() {
		fetchNextIfNull();
		return (next != null);
	}

	public URL nextElement() {
		fetchNextIfNull();

		// save next into a local variable and clear the next field
		URL next = this.next;
		this.next = null;

		// if we didn't have a next throw an exception
		if (next == null) {
			throw new NoSuchElementException();
		}
		return next;
	}

	private void fetchNextIfNull() {
		if (iterator == null) {
			return;
		}
		if (next != null) {
			return;
		}

		try {
			while (iterator.hasNext()) {
				ResourceLocation resourceLocation = iterator.next();
				ResourceHandle resourceHandle = resourceLocation.getResourceHandle(resourceName);
				if (resourceHandle != null) {
					next = resourceHandle.getUrl();
					return;
				}
			}
			// no more elements
			// clear the iterator so it can be GCed
			iterator = null;
		} catch (IllegalStateException e) {
			// Jar file was closed... this means the resource finder was destroyed
			// clear the iterator so it can be GCed
			iterator = null;
			throw e;
		}
	}
}