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Java > Open Source Codes > org > apache > avalon > framework > service > ServiceSelector


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55 package org.apache.avalon.framework.service;
56
57 /**
58  * A <code>ServiceSelector</code> selects {@link Object}s based on a
59  * supplied policy. The contract is that all the {@link Object}s implement the
60  * same role.
61  *
62  * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
63  * @version CVS $Revision: 1.13 $ $Date: 2003/02/11 15:58:42 $
64  * @see org.apache.avalon.framework.service.Serviceable
65  * @see org.apache.avalon.framework.service.ServiceSelector
66  */
67 public interface ServiceSelector
68 {
69     /**
70      * Select the {@link Object} associated with the given policy.
71      * For instance, If the {@link ServiceSelector} has a
72      * <code>Generator</code> stored and referenced by a URL, the
73      * following call could be used:
74      *
75      * <pre>
76      * try
77      * {
78      * Generator input;
79      * input = (Generator)selector.select( new URL("foo://demo/url") );
80      * }
81      * catch (...)
82      * {
83      * ...
84      * }
85      * </pre>
86      *
87      * @param policy A criteria against which a {@link Object} is selected.
88      *
89      * @return an {@link Object} value
90      * @throws ServiceException If the requested {@link Object} cannot be supplied
91      */
92     Object JavaDoc select( Object JavaDoc policy )
93         throws ServiceException;
94
95     /**
96      * Check to see if a {@link Object} exists relative to the supplied policy.
97      *
98      * @param policy a {@link Object} containing the selection criteria
99      * @return True if the component is available, False if it not.
100      */
101     boolean isSelectable( Object JavaDoc policy );
102
103     /**
104      * Return the {@link Object} when you are finished with it. This
105      * allows the {@link ServiceSelector} to handle the End-Of-Life Lifecycle
106      * events associated with the {@link Object}. Please note, that no
107      * Exception should be thrown at this point. This is to allow easy use of the
108      * ServiceSelector system without having to trap Exceptions on a release.
109      *
110      * @param object The {@link Object} we are releasing.
111      */
112     void release( Object JavaDoc object );
113 }
114
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