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.annotations.Beta; 020import com.google.common.base.MoreObjects; 021 022/** 023 * Wraps an event that was posted, but which had no subscribers and thus could not be delivered. 024 * 025 * <p>Registering a DeadEvent subscriber is useful for debugging or logging, as it can detect 026 * misconfigurations in a system's event distribution. 027 * 028 * @author Cliff Biffle 029 * @since 10.0 030 */ 031@Beta 032public class DeadEvent { 033 034 private final Object source; 035 private final Object event; 036 037 /** 038 * Creates a new DeadEvent. 039 * 040 * @param source object broadcasting the DeadEvent (generally the {@link EventBus}). 041 * @param event the event that could not be delivered. 042 */ 043 public DeadEvent(Object source, Object event) { 044 this.source = checkNotNull(source); 045 this.event = checkNotNull(event); 046 } 047 048 /** 049 * Returns the object that originated this event (<em>not</em> the object that originated the 050 * wrapped event). This is generally an {@link EventBus}. 051 * 052 * @return the source of this event. 053 */ 054 public Object getSource() { 055 return source; 056 } 057 058 /** 059 * Returns the wrapped, 'dead' event, which the system was unable to deliver to any registered 060 * subscriber. 061 * 062 * @return the 'dead' event that could not be delivered. 063 */ 064 public Object getEvent() { 065 return event; 066 } 067 068 @Override 069 public String toString() { 070 return MoreObjects.toStringHelper(this).add("source", source).add("event", event).toString(); 071 } 072}