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Common application code (Apache License v2) 2008-2013 Matt Gumbley, DevZendo.org
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/**
 * Copyright (C) 2008-2010 Matt Gumbley, DevZendo.org 
 *
 * 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.devzendo.commonapp.spring.springloader;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * Factory / helper class for obtaining a SpringLoader
 *
 * @author matt
 *
 */
public final class SpringLoaderFactory {
    private static SpringLoader instance;

    /**
     * Thou shalt not instantiate
     */
    private SpringLoaderFactory() {
        // do nothing
    }

    /**
     * @return the singleton instance of the SpringLoader, instantiated
     * with no application contexts.
     * This should be the only singleton in the system.
     */
    public static synchronized SpringLoader getInstance() {
        if (instance == null) {
            initAppContext(new ArrayList ());
        }
        return instance;
    }

    /**
     * @param contextFiles a list of application context files with which
     * to initialise the SpringLoader
     * @return the SpringLoader
     */
    public static SpringLoader initialise(final List  contextFiles) {
        return initAppContext(contextFiles);
    }

    /**
     * @param contextFiles a list of application context files with which
     * to initialise the SpringLoader
     * @return the SpringLoader
     */
    public static SpringLoader initialise(final String... contextFiles) {
        return initAppContext(Arrays.asList(contextFiles));
    }

    private static synchronized SpringLoader initAppContext(final List  contextFiles) {
        // add ourselves in to the list of application contexts
        final List  expandContextFiles = new ArrayList (contextFiles);
        expandContextFiles.add("org/devzendo/commonapp/spring/springloader/SpringLoader.xml");
        // Can't just stash the newly created ClassPathXmlApplicationContext
        // in the SpringLoaderImpl, since this is a static method, so that's
        // why we're ApplicationContextAware.
        final ApplicationContext aC = new ClassPathXmlApplicationContext(expandContextFiles.toArray(new String[0]));
        // use the application context to instantiate a SpringLoader (one of these classes)
        instance = (SpringLoader) aC.getBean("springLoader");
        return instance;
    }
}