1 /*
2 * *************************************************************************************************************************************************************
3 *
4 * TheseFoolishThings: Miscellaneous utilities
5 * http://tidalwave.it/projects/thesefoolishthings
6 *
7 * Copyright (C) 2009 - 2026 by Tidalwave s.a.s. (http://tidalwave.it)
8 *
9 * *************************************************************************************************************************************************************
10 *
11 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
12 * You may obtain a copy of the License at
13 *
14 * http://www.apache.org/licenses/LICENSE-2.0
15 *
16 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
17 * CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
18 *
19 * *************************************************************************************************************************************************************
20 *
21 * git clone https://bitbucket.org/tidalwave/thesefoolishthings-src
22 * git clone https://github.com/tidalwave-it/thesefoolishthings-src
23 *
24 * *************************************************************************************************************************************************************
25 */
26 package it.tidalwave.messagebus;
27
28 import jakarta.annotation.Nonnull;
29
30 /***************************************************************************************************************************************************************
31 * A simple message bus for a local publish/subscribe facility. The topic of a message is a class: a {@link Listener} subscribed to a topic receives the
32 * messages of that class and of its subclasses (or implementations, if the topic is an interface).
33 * @author Fabrizio Giudici
34 **************************************************************************************************************************************************************/
35 public interface MessageBus
36 {
37 /***********************************************************************************************************************************************************
38 * A listener to receive notifications from a {@link MessageBus}.
39 * @param <T> the static type of the topic
40 * @stereotype Listener
41 **********************************************************************************************************************************************************/
42 public static interface Listener<T>
43 {
44 /*******************************************************************************************************************************************************
45 * Notifies the reception of the given message.
46 * @param message the event
47 ******************************************************************************************************************************************************/
48 public void notify (@Nonnull T message);
49 }
50
51 /***********************************************************************************************************************************************************
52 * Publishes the given event. The topic is the class of the event.
53 * @param <T> the static type of the topic
54 * @param message the event
55 **********************************************************************************************************************************************************/
56 public <T> void publish (@Nonnull T message);
57
58 /***********************************************************************************************************************************************************
59 * Publishes the given message and topic. Passing an explicit topic can be useful when dealing with a hierarchy of events (so, perhaps a subclass is passed
60 * but the topic is the root of the hierarchy).
61 * @param <T> the static type of the topic
62 * @param topic the topic
63 * @param message the message
64 **********************************************************************************************************************************************************/
65 public <T> void publish (@Nonnull Class<T> topic, @Nonnull T message);
66
67 /***********************************************************************************************************************************************************
68 * Subscribes a {@link Listener} to a topic.
69 * @param <T> the static type of the topic
70 * @param topic the topic
71 * @param listener the listener
72 **********************************************************************************************************************************************************/
73 public <T> void subscribe (@Nonnull Class<T> topic, @Nonnull Listener<T> listener);
74
75 /***********************************************************************************************************************************************************
76 * Unsubscribes a {@link Listener} from all the topics it was subscribed to.
77 * @param listener the listener
78 **********************************************************************************************************************************************************/
79 public void unsubscribe (@Nonnull Listener<?> listener);
80 }