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The Service Provider Interfaces for developing HiveMQ plugins.

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/*
 * Copyright 2014 dc-square GmbH
 *
 * 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.hivemq.spi.callback.schedule;


import com.hivemq.spi.callback.AsynchronousCallback;
import com.hivemq.spi.callback.registry.CallbackRegistry;

/**
 * This callback gets called periodically based on the value provided in the
 * {@link ScheduledCallback#cronExpression()} method.
 * 
 * This callback is especially useful for recurring tasks like maintenance tasks.
 *
 * @author Dominik Obermaier
 * @since 2.0
 */
public interface ScheduledCallback extends AsynchronousCallback {


    /**
     * This method gets executed on the given schedules
     */
    void execute();

    /**
     * This method returns the quartz-like cron expression for the callback.
     * 
     * Note that this method only gets called once when adding the callback to the
     * {@link CallbackRegistry}. If you have dynamic
     * cron expressions in this method, you must manually call the
     * {@link CallbackRegistry#reloadScheduledCallbackExpression(ScheduledCallback)}
     * method in order to reload the expression
     *
     * @return a String which contains the quartz-like cron expressions.
     * @see 
     *      Documentation for quartz cron expressions
     */
    String cronExpression();
}