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


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55 package org.apache.avalon.framework.service;
56
57 /**
58  * A <code>ServiceManager</code> selects <code>Object</code>s based on a
59  * role. The contract is that all the <code>Object</code>s implement the
60  * differing roles and there is one <code>Object</code> per role. If you
61  * need to select on of many <code>Object</code>s that implement the same
62  * role, then you need to use a <code>ServiceSelector</code>. Roles are
63  * usually the full interface name.
64  *
65  * A role is better understood by the analogy of a play. There are many
66  * different roles in a script. Any actor or actress can play any given part
67  * and you get the same results (phrases said, movements made, etc.). The exact
68  * nuances of the performance is different.
69  *
70  * Below is a list of things that might be considered the different roles:
71  *
72  * <ul>
73  * <li> InputAdapter and OutputAdapter</li>
74  * <li> Store and Spool</li>
75  * </ul>
76  *
77  * The <code>ServiceManager</code> does not specify the methodology of
78  * getting the <code>Object</code>, merely the interface used to get it.
79  * Therefore the <code>ServiceManager</code> can be implemented with a
80  * factory pattern, an object pool, or a simple Hashtable.
81  *
82  * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
83  * @version CVS $Revision: 1.14 $ $Date: 2003/02/11 15:58:42 $
84  * @see org.apache.avalon.framework.service.Serviceable
85  * @see org.apache.avalon.framework.service.ServiceSelector
86  */
87 public interface ServiceManager
88 {
89     /**
90      * Get the <code>Object</code> associated with the given key. For
91      * instance, If the <code>ServiceManager</code> had a
92      * <code>LoggerComponent</code> stored and referenced by key,
93      * the following could be used:
94      * <pre>
95      * try
96      * {
97      * LoggerComponent log;
98      * myComponent = (LoggerComponent) manager.lookup( LoggerComponent.ROLE );
99      * }
100      * catch (...)
101      * {
102      * ...
103      * }
104      * </pre>
105      *
106      * @param key The lookup key of the <code>Object</code> to retrieve.
107      * @return an <code>Object</code> value
108      * @throws ServiceException if an error occurs
109      */
110     Object JavaDoc lookup( String JavaDoc key )
111         throws ServiceException;
112
113     /**
114      * Check to see if a <code>Object</code> exists for a key.
115      *
116      * @param key a string identifying the key to check.
117      * @return True if the object exists, False if it does not.
118      */
119     boolean hasService( String JavaDoc key );
120
121     /**
122      * Return the <code>Object</code> when you are finished with it. This
123      * allows the <code>ServiceManager</code> to handle the End-Of-Life Lifecycle
124      * events associated with the <code>Object</code>. Please note, that no
125      * Exception should be thrown at this point. This is to allow easy use of the
126      * ServiceManager system without having to trap Exceptions on a release.
127      *
128      * @param object The <code>Object</code> we are releasing.
129      */
130     void release( Object JavaDoc object );
131 }
132
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