001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2.event;
018
019import java.util.EventObject;
020
021/**
022 * <p>
023 * The base class for all events generated by this library.
024 * </p>
025 * <p>
026 * The events produced by objects in this library are arranged in an inheritance hierarchy. This base class defines some
027 * basic properties common to all configuration events. Especially, an event has an {@link EventType} which describes
028 * its semantics. The event type can also be used for filtering for events or for defining event listeners on a
029 * fine-grained basis.
030 * </p>
031 *
032 * @since 2.0
033 */
034public class Event extends EventObject {
035
036    /**
037     * The root event type for all configuration-related events. All specific event types have this type as super direct
038     * (directly or indirectly).
039     */
040    public static final EventType<Event> ANY = new EventType<>(null, "ANY");
041
042    private static final long serialVersionUID = -8168310049858198944L;
043
044    /**
045     * Constant for the format used in toString() for a property representation.
046     */
047    private static final String FMT_PROPERTY = " %s=%s";
048
049    /**
050     * Constant for the initial buffer size for the generation of the string representation.
051     */
052    private static final int BUF_SIZE = 256;
053
054    /** The type of this event. */
055    private final EventType<? extends Event> eventType;
056
057    /**
058     * Creates a new instance of {@code Event} and sets basic properties.
059     *
060     * @param source the object on which the Event initially occurred (must not be <b>null</b>)
061     * @param evType the type of this event (must not be <b>null</b>)
062     * @throws IllegalArgumentException if a required parameter is null
063     */
064    public Event(final Object source, final EventType<? extends Event> evType) {
065        super(source);
066        if (evType == null) {
067            throw new IllegalArgumentException("Event type must not be null!");
068        }
069        eventType = evType;
070    }
071
072    /**
073     * Helper method for appending a representation for a property to the overall string representation for this object.
074     * This method is called by {@code toString()} for generating string fragments for the properties of this class. It can
075     * also be used by derived classes which extend the string representation of this base class.
076     *
077     * @param buf the target buffer
078     * @param property the name of the property
079     * @param value the property value
080     */
081    protected void appendPropertyRepresentation(final StringBuilder buf, final String property, final Object value) {
082        buf.append(String.format(FMT_PROPERTY, property, String.valueOf(value)));
083    }
084
085    /**
086     * Gets the type of this event.
087     *
088     * @return the event type
089     */
090    public EventType<? extends Event> getEventType() {
091        return eventType;
092    }
093
094    /**
095     * Returns a string representation for this object. This string contains the event class and a list of all properties.
096     *
097     * @return a string for this object
098     */
099    @Override
100    public String toString() {
101        final StringBuilder buf = new StringBuilder(BUF_SIZE);
102        buf.append(getClass().getSimpleName());
103        buf.append(" [");
104        appendPropertyRepresentation(buf, "source", getSource());
105        appendPropertyRepresentation(buf, "eventType", getEventType());
106        buf.append(" ]");
107        return buf.toString();
108    }
109}