servicebinder/src/main/java/org/apache/felix/servicebinder/InstanceReferenceListener.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.felix.servicebinder;

/**
 * This is an event listener for listening to changes in
 * the availability of the underlying object associated
 * with an <tt>InstanceReference</tt>. For the precise
 * details of when this event is fired, refer to the
 * methods below.
 * 
 * @author <a href="mailto:dev@felix.apache.org">Felix Project Team</a>
**/
public interface InstanceReferenceListener extends java.util.EventListener
{
    /**
     * This method is called when an <tt>InstanceReference</tt>'s
     * underlying object becomes valid, i.e., the instance is
     * available for use. This event is fired during the following
     * sequence of steps:
     * <p>
     * <ol>
     *   <li>Instance created.</li>
     *   <li>Dependencies bound, if any.</li>
     *   <li>Services registered, if any.</li>
     *   <li><tt>Lifecycle.activate()</tt> is called, if the instance
     *       implements the <tt>Lifecycle</tt> interface.</li>
     *   <li>Fire <tt>InstanceReferenceListener.validated()</tt>.
     * </ol>
     * @param event the associated instance reference event.
    **/
    public void validated(InstanceReferenceEvent event);

    /**
     * This method is called when an <tt>InstanceReference</tt>'s
     * underlying object is going to be invalidated. This event
     * is fired during the following sequence of steps:
     * <p>
     * <ol>
     *   <li>Fire <tt>InstanceReferenceListener.invalidating()</tt>.
     *   <li>Call <tt>Lifecycle.deactivate()</tt>, if the instance
     *       implements the <tt>Lifecycle</tt> interface.</li>
     *   <li>Unregister services, if any.</li>
     *   <li>Unbind dependencies, if any.</li>
     *   <li>Dispose instance.</li>
     * </ol>
     * <p>
     * Note: Care must be taken during this callback, because the
     * underlying object associated with the instance reference may
     * not be fully functioning. For example, this event might be
     * fired in direct response to a dependent service shutting down,
     * which then instigates the invalidation of the underlying object
     * instance.
     * @param event the associated instance reference event.
    **/
    public void invalidating(InstanceReferenceEvent event);
}