001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.reloading;
018
019/**
020 * <p>
021 * An interface to be implemented by objects which can detect whether a reload operation is required.
022 * </p>
023 * <p>
024 * This interface is used by a {@link ReloadingController} object. When a reloading check is to be performed, it is
025 * delegated to a concrete implementation. The implementation decides whether (specific) criteria for a reload are
026 * fulfilled, so that the controller can react accordingly.
027 * </p>
028 * <p>
029 * This interface does not define how a check for a reload is performed. This is completely up to a concrete
030 * implementation. There is just one method for executing the check and one method to notify the
031 * {@code ReloadingDetector} that the reload actually happened; this method can be used to reset the internal state so
032 * that the conditions for the next reload can be detected.
033 * </p>
034 * <p>
035 * When used together with {@code ReloadingController} an implementation does not have to be thread-safe. The controller
036 * takes care for synchronization so that an instance is accessed by a single thread only.
037 * </p>
038 *
039 * @since 2.0
040 */
041public interface ReloadingDetector {
042    /**
043     * Checks whether all criteria for a reload operation are fulfilled. This method is called by external components to
044     * find out when reloading should take place.
045     *
046     * @return <strong>true</strong> if a reload operation should be performed, <strong>false</strong> otherwise
047     */
048    boolean isReloadingRequired();
049
050    /**
051     * Notifies this object that a reload operation has been performed. This method is called after
052     * {@code reloadingRequired()} has returned <strong>true</strong>. It can be used to reset internal state in order to detect the
053     * next reload operation.
054     */
055    void reloadingPerformed();
056}