1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.configuration2.event;
18
19 import java.util.EventObject;
20
21 /**
22 * <p>
23 * The base class for all events generated by this library.
24 * </p>
25 * <p>
26 * The events produced by objects in this library are arranged in an inheritance hierarchy. This base class defines some
27 * basic properties common to all configuration events. Especially, an event has an {@link EventType} which describes
28 * its semantics. The event type can also be used for filtering for events or for defining event listeners on a
29 * fine-grained basis.
30 * </p>
31 *
32 * @since 2.0
33 */
34 public class Event extends EventObject {
35
36 /**
37 * The root event type for all configuration-related events. All specific event types have this type as super direct
38 * (directly or indirectly).
39 */
40 public static final EventType<Event> ANY = new EventType<>(null, "ANY");
41
42 private static final long serialVersionUID = -8168310049858198944L;
43
44 /**
45 * Constant for the format used in toString() for a property representation.
46 */
47 private static final String FMT_PROPERTY = " %s=%s";
48
49 /**
50 * Constant for the initial buffer size for the generation of the string representation.
51 */
52 private static final int BUF_SIZE = 256;
53
54 /** The type of this event. */
55 private final EventType<? extends Event> eventType;
56
57 /**
58 * Creates a new instance of {@code Event} and sets basic properties.
59 *
60 * @param source the object on which the Event initially occurred (must not be <b>null</b>)
61 * @param evType the type of this event (must not be <b>null</b>)
62 * @throws IllegalArgumentException if a required parameter is null
63 */
64 public Event(final Object source, final EventType<? extends Event> evType) {
65 super(source);
66 if (evType == null) {
67 throw new IllegalArgumentException("Event type must not be null!");
68 }
69 eventType = evType;
70 }
71
72 /**
73 * Gets the type of this event.
74 *
75 * @return the event type
76 */
77 public EventType<? extends Event> getEventType() {
78 return eventType;
79 }
80
81 /**
82 * Returns a string representation for this object. This string contains the event class and a list of all properties.
83 *
84 * @return a string for this object
85 */
86 @Override
87 public String toString() {
88 final StringBuilder buf = new StringBuilder(BUF_SIZE);
89 buf.append(getClass().getSimpleName());
90 buf.append(" [");
91 appendPropertyRepresentation(buf, "source", getSource());
92 appendPropertyRepresentation(buf, "eventType", getEventType());
93 buf.append(" ]");
94 return buf.toString();
95 }
96
97 /**
98 * Helper method for appending a representation for a property to the overall string representation for this object.
99 * This method is called by {@code toString()} for generating string fragments for the properties of this class. It can
100 * also be used by derived classes which extend the string representation of this base class.
101 *
102 * @param buf the target buffer
103 * @param property the name of the property
104 * @param value the property value
105 */
106 protected void appendPropertyRepresentation(final StringBuilder buf, final String property, final Object value) {
107 buf.append(String.format(FMT_PROPERTY, property, String.valueOf(value)));
108 }
109 }