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/*
 * Copyright 2004-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.webflow.execution;

import java.util.EventObject;

import org.springframework.util.Assert;
import org.springframework.webflow.core.collection.AttributeMap;
import org.springframework.webflow.core.collection.CollectionUtils;

/**
 * Signals the occurrence of something an active flow execution should respond to. Each event has a string id that
 * provides a key for identifying what happened: e.g "coinInserted", or "pinDropped". Events may have attributes that
 * provide arbitrary payload data, e.g. "coin.amount=25", or "pinDropSpeed=25ms".
 * 

* As an example, a "submit" event might signal that a Submit button was pressed in a web browser. A "success" event * might signal an action executed successfully. A "finish" event might signal a subflow ended normally. *

* Why is this not an interface? A specific design choice. An event is not a strategy that defines a generic type or * role--it is essentially an immutable value object. It is expected that specializations of this base class be "Events" * and not part of some other inheritance hierarchy. * * @author Keith Donald * @author Erwin Vervaet * @author Colin Sampaleanu */ public class Event extends EventObject { /** * The event identifier. */ private final String id; /** * The time the event occurred. */ private final long timestamp = System.currentTimeMillis(); /** * Additional event attributes that form this event's payload. */ private final AttributeMap attributes; /** * Create a new event with the specified id and no payload. * @param source the source of the event (required) * @param id the event identifier (required) */ public Event(Object source, String id) { this(source, id, null); } /** * Create a new event with the specified id and payload attributes. * @param source the source of the event (required) * @param id the event identifier (required) * @param attributes additional event attributes */ public Event(Object source, String id, AttributeMap attributes) { super(source); Assert.hasText(id, "The event id is required: please set this event's id to a non-blank string identifier"); this.id = id; this.attributes = attributes != null ? attributes : CollectionUtils.EMPTY_ATTRIBUTE_MAP; } /** * Returns the event identifier. * @return the event id */ public String getId() { return id; } /** * Returns the time at which the event occurred, represented as the number of milliseconds since January 1, 1970, * 00:00:00 GMT. * @return the timestamp */ public long getTimestamp() { return timestamp; } /** * Returns an unmodifiable map storing the attributes of this event. Never returns null. * @return the event attributes (payload) */ public AttributeMap getAttributes() { return attributes; } public String toString() { return getId(); } }