1 /*
2  * Copyright (C) 2007 The Guava Authors
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.google.common.eventbus;
18 
19 import static com.google.common.base.Preconditions.checkNotNull;
20 
21 import com.google.common.annotations.Beta;
22 
23 /**
24  * Wraps an event that was posted, but which had no subscribers and thus could
25  * not be delivered.
26  *
27  * <p>Registering a DeadEvent subscriber is useful for debugging or logging, as
28  * it can detect misconfigurations in a system's event distribution.
29  *
30  * @author Cliff Biffle
31  * @since 10.0
32  */
33 @Beta
34 public class DeadEvent {
35 
36   private final Object source;
37   private final Object event;
38 
39   /**
40    * Creates a new DeadEvent.
41    *
42    * @param source  object broadcasting the DeadEvent (generally the
43    *                {@link EventBus}).
44    * @param event   the event that could not be delivered.
45    */
DeadEvent(Object source, Object event)46   public DeadEvent(Object source, Object event) {
47     this.source = checkNotNull(source);
48     this.event = checkNotNull(event);
49   }
50 
51   /**
52    * Returns the object that originated this event (<em>not</em> the object that
53    * originated the wrapped event).  This is generally an {@link EventBus}.
54    *
55    * @return the source of this event.
56    */
getSource()57   public Object getSource() {
58     return source;
59   }
60 
61   /**
62    * Returns the wrapped, 'dead' event, which the system was unable to deliver
63    * to any registered subscriber.
64    *
65    * @return the 'dead' event that could not be delivered.
66    */
getEvent()67   public Object getEvent() {
68     return event;
69   }
70 
71 }
72