    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
    027 * hierarchy. This base class defines some basic properties common to all
    028 * configuration events. Especially, an event has an {@link EventType} which
    029 * describes its semantics. The event type can also be used for filtering for
    030 * events or for defining event listeners on a fine-grained basis.
    031 * </p>
    032 *
    033 * @since 2.0
    034 */
    035public class Event extends EventObject
    036{
    037    /**
    038     * The root event type for all configuration-related events. All specific
    039     * event types have this type as super direct (directly or indirectly).
    040     */
    041    public static final EventType<Event> ANY =
    042            new EventType<>(null, "ANY");
    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
    051     * representation.
    052     */
    053    private static final int BUF_SIZE = 256;
    054
    055    /** The type of this event. */
    056    private final EventType<? extends Event> eventType;
    057
    058    /**
    059     * Creates a new instance of {@code Event} and sets basic properties.
    060     *
    061     * @param source the object on which the Event initially occurred (must not
    062     *        be <b>null</b>)
    063     * @param evType the type of this event (must not be <b>null</b>)
    064     * @throws IllegalArgumentException if a required parameter is null
    065     */
    066    public Event(final Object source, final EventType<? extends Event> evType)
    067    {
    068        super(source);
    069        if (evType == null)
    070        {
    071            throw new IllegalArgumentException("Event type must not be null!");
    072        }
    073        eventType = evType;
    074    }
    075
    076    /**
    077     * Returns the type of this event.
    078     *
    079     * @return the event type
    080     */
    081    public EventType<? extends Event> getEventType()
    082    {
    083        return eventType;
    084    }
    085
    086    /**
    087     * Returns a string representation for this object. This string contains the
    088     * event class and a list of all properties.
    089     *
    090     * @return a string for this object
    091     */
    092    @Override
    093    public String toString()
    094    {
    095        final StringBuilder buf = new StringBuilder(BUF_SIZE);
    096        buf.append(getClass().getSimpleName());
    097        buf.append(" [");
    098        appendPropertyRepresentation(buf, "source", getSource());
    099        appendPropertyRepresentation(buf, "eventType", getEventType());
    100        buf.append(" ]");
    101        return buf.toString();
    102    }
    103
    104    /**
    105     * Helper method for appending a representation for a property to the
    106     * overall string representation for this object. This method is called by
    107     * {@code toString()} for generating string fragments for the properties of
    108     * this class. It can also be used by derived classes which extend the
    109     * string representation of this base class.
    110     *
    111     * @param buf the target buffer
    112     * @param property the name of the property
    113     * @param value the property value
    114     */
    115    protected void appendPropertyRepresentation(final StringBuilder buf,
    116            final String property, final Object value)
    117    {
    118        buf.append(String.format(FMT_PROPERTY, property, String.valueOf(value)));
    119    }
    120}