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The backport-spi library is backport of Service Provider Interface to Java5 with extra features.
There is a newer version: 1.0.1
/*
 *    Copyright 2010 The backport-spi Team
 *
 *    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 com.googlecode.bspi;

import java.io.Closeable;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.Enumeration;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.NoSuchElementException;

/**
 * 
 * @version $Id: ServiceIterator.java 4 2010-07-24 18:45:26Z simone.tripodi $
 * @param 
 */
final class ServiceIterator implements Iterator {

    private static final Charset UTF_8 = Charset.forName("UTF-8");

    private final Class service;

    private final ClassLoader classLoader;

    private final Enumeration serviceResources;

    private final LinkedHashMap providers;

    private Iterator pending = null;

    private String nextName = null;

    public ServiceIterator(Class service,
            ClassLoader classLoader,
            Enumeration serviceResources,
            LinkedHashMap providers) {
        this.service = service;
        this.classLoader = classLoader;
        this.serviceResources = serviceResources;
        this.providers = providers;
    }

    public boolean hasNext() {
        if (this.nextName != null) {
            return true;
        }

        while ((this.pending == null) || !this.pending.hasNext()) {
            if (!serviceResources.hasMoreElements()) {
                return false;
            }
            this.pending = parseServiceFile(this.serviceResources.nextElement());
        }

        this.nextName = this.pending.next();
        return true;
    }

    public S next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }
        String className = this.nextName;
        this.nextName = null;
        try {
            S provider = this.service.cast(
                    Class.forName(className, true, this.classLoader).newInstance());
            providers.put(className, provider);
            return provider;
        } catch (ClassNotFoundException e) {
            throw new ServiceConfigurationError("Provider '"
                    + className
                    + "' not found", e);
        } catch (ClassCastException e) {
            throw new ServiceConfigurationError("Provider '"
                    + className
                    + "' is not assignable to Service '"
                    + this.service.getName()
                    + "'", e);
        } catch (Throwable e) {
            throw new ServiceConfigurationError("Provider '"
                    + className
                    + "' could not be instantiated", e);
        }
    }

    public void remove() {
        throw new UnsupportedOperationException();
    }

    private Iterator parseServiceFile(URL url) {
        InputStream inputStream = null;
        Reader reader = null;
        try {
            inputStream = url.openStream();
            reader = new InputStreamReader(inputStream, UTF_8);
            ServiceFileParser serviceFileParser = new ServiceFileParser(reader);
            serviceFileParser.setProviders(this.providers);
            serviceFileParser.parse();
            return serviceFileParser.iterator();
        } catch (Exception e) {
            throw new ServiceConfigurationError("An error occurred while reading service resource '"
                    + url
                    + "' for service class '"
                    + this.service.getName()
                    + "'", e);
        } finally {
            closeQuietly(reader);
            closeQuietly(inputStream);
        }
    }

    private static void closeQuietly(Closeable closeable) {
        if (closeable != null) {
            try {
                closeable.close();
            } catch (IOException e) {
                // close quietly
            }
        }
    }

}