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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  }