1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 */
19 package org.apache.shiro.event.support;
20
21 /**
22 * An event listener knows how to accept and process events of a particular type (or types).
23 * <p/>
24 * Note that this interface is in the event implementation support package (and not the event package directly)
25 * because it is a supporting concept for event bus implementations and not something that most application
26 * developers using Shiro should implement directly. App developers should instead use the
27 * {@link org.apache.shiro.event.Subscribe Subscribe} annotation on methods they wish to receive events.
28 * <p/>
29 * This interface therefore mainly represents a 'middle man' between the event bus and the actual subscribing
30 * component. As such, event bus implementors (or framework/infrastructural implementors) or those that wish to
31 * customize listener/dispatch functionality might find this concept useful.
32 * <p/>
33 * It is a concept almost always used in conjunction with a {@link EventListenerResolver} implementation.
34 *
35 * @see SingleArgumentMethodEventListener
36 * @see AnnotationEventListenerResolver
37 *
38 * @since 1.3
39 */
40 public interface EventListener {
41
42 /**
43 * Returns {@code true} if the listener instance can process the specified event object, {@code false} otherwise.
44 * @param event the event object to test
45 * @return {@code true} if the listener instance can process the specified event object, {@code false} otherwise.
46 */
47 boolean accepts(Object event);
48
49 /**
50 * Handles the specified event. Again, as this interface is an implementation concept, implementations of this
51 * method will likely dispatch the event to a 'real' processor (e.g. method).
52 *
53 * @param event the event to handle.
54 */
55 void onEvent(Object event);
56 }