001/*
002 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved.
003 *
004 * Project and contact information: http://www.cascading.org/
005 *
006 * This file is part of the Cascading project.
007 *
008 * Licensed under the Apache License, Version 2.0 (the "License");
009 * you may not use this file except in compliance with the License.
010 * You may obtain a copy of the License at
011 *
012 *     http://www.apache.org/licenses/LICENSE-2.0
013 *
014 * Unless required by applicable law or agreed to in writing, software
015 * distributed under the License is distributed on an "AS IS" BASIS,
016 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
017 * See the License for the specific language governing permissions and
018 * limitations under the License.
019 */
020
021package cascading.flow;
022
023/**
024 * Interface FlowListener provides hooks for receiving events on various stages of a {@link Flow} execution.
025 * <p/>
026 * Any {@link RuntimeException} thrown from any of the listener methods will force the given {@code flow} to
027 * stop by calling {@link Flow#stop()}.
028 */
029public interface FlowListener
030  {
031  /**
032   * The onStarting event is fired when a Flow instance receives the start() message.
033   *
034   * @param flow
035   */
036  void onStarting( Flow flow );
037
038  /**
039   * The onStopping event is fired when a Flow instance receives the stop() message.
040   *
041   * @param flow
042   */
043  void onStopping( Flow flow );
044
045  /**
046   * The onCompleted event is fired when a Flow instance has completed all work whether if was success or failed. If
047   * there was a thrown exception, onThrowable will be fired before this event.
048   *
049   * @param flow
050   */
051  void onCompleted( Flow flow );
052
053  /**
054   * The onThrowable event is fired if any child {@link cascading.flow.FlowStep} throws a Throwable type. This throwable is passed
055   * as an argument to the event. This event method should return true if the given throwable was handled and should
056   * not be rethrown from the {@link Flow#complete()} method.
057   *
058   * @param flow
059   * @param throwable
060   * @return returns true if this listener has handled the given throwable
061   */
062  boolean onThrowable( Flow flow, Throwable throwable );
063  }