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002 * Licensed to the Apache Software Foundation (ASF) under one   *
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004 * distributed with this work for additional information        *
005 * regarding copyright ownership.  The ASF licenses this file   *
006 * to you under the Apache License, Version 2.0 (the            *
007 * "License"); you may not use this file except in compliance   *
008 * with the License.  You may obtain a copy of the License at   *
009 *                                                              *
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019
020package org.apache.james.mime4j.storage;
021
022/**
023 * Allows for a default {@link StorageProvider} instance to be configured on an
024 * application level.
025 * <p>
026 * The default instance can be set by either calling
027 * {@link #setInstance(StorageProvider)} when the application starts up or by
028 * setting the system property
029 * <code>org.apache.james.mime4j.defaultStorageProvider</code> to the class
030 * name of a <code>StorageProvider</code> implementation.
031 * <p>
032 * If neither option is used or if the class instantiation fails this class
033 * provides a pre-configured default instance.
034 */
035public class DefaultStorageProvider {
036
037    /** Value is <code>org.apache.james.mime4j.defaultStorageProvider</code> */
038    public static final String DEFAULT_STORAGE_PROVIDER_PROPERTY =
039        "org.apache.james.mime4j.defaultStorageProvider";
040
041    private static volatile StorageProvider instance = null;
042
043    static {
044        initialize();
045    }
046
047    private DefaultStorageProvider() {
048    }
049
050    /**
051     * Returns the default {@link StorageProvider} instance.
052     *
053     * @return the default {@link StorageProvider} instance.
054     */
055    public static StorageProvider getInstance() {
056        return instance;
057    }
058
059    /**
060     * Sets the default {@link StorageProvider} instance.
061     *
062     * @param instance
063     *            the default {@link StorageProvider} instance.
064     */
065    public static void setInstance(StorageProvider instance) {
066        if (instance == null) {
067            throw new IllegalArgumentException();
068        }
069
070        DefaultStorageProvider.instance = instance;
071    }
072
073    private static void initialize() {
074        String clazz = System.getProperty(DEFAULT_STORAGE_PROVIDER_PROPERTY);
075        try {
076            if (clazz != null) {
077                instance = (StorageProvider) Class.forName(clazz).newInstance();
078            }
079        } catch (Exception e) {
080        }
081        if (instance == null) {
082            StorageProvider backend = new TempFileStorageProvider();
083            instance = new ThresholdStorageProvider(backend, 1024);
084        }
085    }
086
087    // for unit tests only
088    static void reset() {
089        instance = null;
090        initialize();
091    }
092
093}