1 /*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.eventbus;
16
17 import static com.google.common.base.Preconditions.checkNotNull;
18
19 import com.google.common.base.MoreObjects;
20
21 /**
22 * Wraps an event that was posted, but which had no subscribers and thus could not be delivered.
23 *
24 * <p>Registering a DeadEvent subscriber is useful for debugging or logging, as it can detect
25 * misconfigurations in a system's event distribution.
26 *
27 * @author Cliff Biffle
28 * @since 10.0
29 */
30 @ElementTypesAreNonnullByDefault
31 public class DeadEvent {
32
33 private final Object source;
34 private final Object event;
35
36 /**
37 * Creates a new DeadEvent.
38 *
39 * @param source object broadcasting the DeadEvent (generally the {@link EventBus}).
40 * @param event the event that could not be delivered.
41 */
42 public DeadEvent(Object source, Object event) {
43 this.source = checkNotNull(source);
44 this.event = checkNotNull(event);
45 }
46
47 /**
48 * Returns the object that originated this event (<em>not</em> the object that originated the
49 * wrapped event). This is generally an {@link EventBus}.
50 *
51 * @return the source of this event.
52 */
53 public Object getSource() {
54 return source;
55 }
56
57 /**
58 * Returns the wrapped, 'dead' event, which the system was unable to deliver to any registered
59 * subscriber.
60 *
61 * @return the 'dead' event that could not be delivered.
62 */
63 public Object getEvent() {
64 return event;
65 }
66
67 @Override
68 public String toString() {
69 return MoreObjects.toStringHelper(this).add("source", source).add("event", event).toString();
70 }
71 }