AvailabilityAware


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3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *     http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.avalon.framework.availability;
18  
19  
20  /** An Availability contract between the container and the component.
21   *
22   * <p>A component that implements AvailabilityAware, is capable to be notified
23   * that components that it has previously looked up via the 
24   * ServiceManager.lookup() method are made available and non-available, 
25   * and can gracefully handle unavailability.</p>
26   *
27   * <p>Containers are only required to support this interface, if the
28   * container supports dynamic loading/unloading of components, hot-deploys,
29   * remote components and similar cases where components may disappear for
30   * a shorter or longer period of time.</p>
31   *
32   * @since 4.5
33   *
34   * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
35   * @version $Id$
36   */
37  public interface AvailabilityAware
38  {
39      /** Notification that component is available.
40       * <p>The component that previously has been looked up in the 
41       * ServiceManager, using <i>key</i> is now available. This method can 
42       * either be called after the componentUnavailable() method signalled that 
43       * a component is no longer available, OR if the ServiceManager.lookup() 
44       * returned a null (optional lookup) indicating that the requested 
45       * component didn't exist.</p>
46       * <p>
47       *   This method will NOT be called with a <i>key</i> argument that has
48       *   not been used in a ServiceManager.lookup() previously.
49       * </p>
50       *
51       * @param key The key that was used to lookup the component in the 
52       *            ServiceManager earlier.
53       */
54      void componentAvailable( String   key );
55      
56      /** Notification that component is no longer available.
57       * <p>The component that previously has been looked up in the 
58       * ServiceManager, using <i>key</i> is no longer available. The container 
59       * does not place any restrictions on how long the component will be 
60       * unavailble, and the AvailabilityAware component, must employ one or more
61       * strategies on how to gracefully handle short and long absences of 
62       * dependent components. </p>
63       * <p>
64       *   This method will NOT be called with a <i>key</i> argument that has
65       *   not been used in a ServiceManager.lookup() previously.
66       * </p>
67       *
68       * @param key The key that was used to lookup the component in the 
69       *            ServiceManager earlier.
70       */
71      void componentUnavailable( String   key );
72  }
73
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