EventListenerComparator.java
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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.apache.shiro.event.support;
import java.util.Comparator;
/**
* Compares two event listeners to determine the order in which they should be invoked when an event is dispatched.
* The lower the order, the sooner it will be invoked (the higher its precedence). The higher the order, the later
* it will be invoked (the lower its precedence).
* <p/>
* TypedEventListeners have a higher precedence (i.e. a lower order) than standard EventListener instances. Standard
* EventListener instances have the same order priority.
* <p/>
* When both objects being compared are TypedEventListeners, they are ordered according to the rules of the
* {@link EventClassComparator}, using the TypedEventListeners'
* {@link TypedEventListener#getEventType() eventType}.
*
* @since 1.3
*/
public class EventListenerComparator implements Comparator<EventListener> {
//event class comparator is stateless, so we can retain an instance:
private static final EventClassComparator EVENT_CLASS_COMPARATOR = new EventClassComparator();
public int compare(EventListener a, EventListener b) {
if (a == null) {
if (b == null) {
return 0;
} else {
return -1;
}
} else if (b == null) {
return 1;
} else if (a == b || a.equals(b)) {
return 0;
} else {
if (a instanceof TypedEventListener) {
TypedEventListener ta = (TypedEventListener)a;
if (b instanceof TypedEventListener) {
TypedEventListener tb = (TypedEventListener)b;
return EVENT_CLASS_COMPARATOR.compare(ta.getEventType(), tb.getEventType());
} else {
return -1; //TypedEventListeners are 'less than' (higher priority) than non typed
}
} else {
if (b instanceof TypedEventListener) {
return 1;
} else {
return 0;
}
}
}
}
}