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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.commons.text.lookup;

import java.util.ResourceBundle;

/**
 * Looks up keys from resource bundles.
 * 
 * Looks up the value for a given key in the format "BundleName:BundleKey".
 * 
 * 
 * For example: "com.domain.messages:MyKey".
 * 
 *
 * @see ResourceBundle
 * @since 1.3
 */
final class ResourceBundleStringLookup extends AbstractStringLookup {

    /**
     * Defines the singleton for this class.
     */
    static final ResourceBundleStringLookup INSTANCE = new ResourceBundleStringLookup();

    /**
     * No need to build instances for now.
     */
    private ResourceBundleStringLookup() {
        // empty
    }

    /**
     * Looks up the value for the key in the format "BundleName:BundleKey".
     *
     * For example: "com.domain.messages:MyKey".
     *
     * @param key
     *            the key to be looked up, may be null
     * @return The value associated with the key.
     * @see ResourceBundle
     * @see ResourceBundle#getBundle(String)
     * @see ResourceBundle#getString(String)
     */
    @Override
    public String lookup(final String key) {
        if (key == null) {
            return null;
        }
        final String[] keys = key.split(":");
        final int keyLen = keys.length;
        if (keyLen != 2) {
            throw IllegalArgumentExceptions
                    .format("Bad ResourceBundle key format [%s]. Expected format is BundleName:KeyName.", key);
        }
        final String bundleName = keys[0];
        final String bundleKey = keys[1];
        try {
            // The ResourceBundle class caches bundles, no need to cache here.
            return ResourceBundle.getBundle(bundleName).getString(bundleKey);
        } catch (final Exception e) {
            throw IllegalArgumentExceptions.format(e, "Error looking up ResourceBundle [%s] and key [%s].", bundleName,
                    bundleKey);
        }
    }

}