001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.eventbus;
016
017import static com.google.common.base.Preconditions.checkNotNull;
018
019import com.google.common.base.MoreObjects;
020
021/**
022 * Wraps an event that was posted, but which had no subscribers and thus could not be delivered.
023 *
024 * <p>Registering a DeadEvent subscriber is useful for debugging or logging, as it can detect
025 * misconfigurations in a system's event distribution.
026 *
027 * @author Cliff Biffle
028 * @since 10.0
029 */
030public class DeadEvent {
031
032  private final Object source;
033  private final Object event;
034
035  /**
036   * Creates a new DeadEvent.
037   *
038   * @param source object broadcasting the DeadEvent (generally the {@link EventBus}).
039   * @param event the event that could not be delivered.
040   */
041  public DeadEvent(Object source, Object event) {
042    this.source = checkNotNull(source);
043    this.event = checkNotNull(event);
044  }
045
046  /**
047   * Returns the object that originated this event (<em>not</em> the object that originated the
048   * wrapped event). This is generally an {@link EventBus}.
049   *
050   * @return the source of this event.
051   */
052  public Object getSource() {
053    return source;
054  }
055
056  /**
057   * Returns the wrapped, 'dead' event, which the system was unable to deliver to any registered
058   * subscriber.
059   *
060   * @return the 'dead' event that could not be delivered.
061   */
062  public Object getEvent() {
063    return event;
064  }
065
066  @Override
067  public String toString() {
068    return MoreObjects.toStringHelper(this).add("source", source).add("event", event).toString();
069  }
070}