xbean-classloader/src/main/java/org/apache/xbean/classloader/ResourceEnumeration.java

/**
 *
 * Copyright 2005 The Apache Software Foundation
 *
 *  Licensed 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.util.Enumeration;
import java.util.Iterator;
import java.util.Collection;
import java.util.NoSuchElementException;

/**
 * @version $Rev$ $Date: 2006-06-01 06:35:48 +0200 (Thu, 01 Jun 2006) $
 */
public class ResourceEnumeration implements Enumeration {
    private Iterator iterator;
    private final String resourceName;
    private Object next;

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

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

    public Object nextElement() {
        fetchNext();

        // save next into a local variable and clear the next field
        Object 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 fetchNext() {
        if (iterator == null) {
            return;
        }
        if (next != null) {
            return;
        }

        try {
            while (iterator.hasNext()) {
                ResourceLocation 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;
        }
    }
}