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


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55
56 package org.apache.avalon.framework.service;
57
58 import org.apache.avalon.framework.component.Component;
59 import org.apache.avalon.framework.component.ComponentException;
60 import org.apache.avalon.framework.component.ComponentSelector;
61
62 /**
63  * This is a {@link ServiceSelector} implementation that can wrap around a legacy
64  * {@link ComponentSelector} object effectively adapting a {@link ComponentSelector}
65  * interface to a {@link ServiceSelector} interface.
66  * <p>
67  * This class implements the {@link Component} interface because it is used in
68  * environments which expect all components to implement Component.
69  *
70  * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
71  * @version CVS $Revision: 1.7 $ $Date: 2003/02/10 07:19:18 $
72  */
73 public class WrapperServiceSelector
74     implements ServiceSelector
75 {
76     /**
77      * The Selector we are wrapping.
78      */
79     private final ComponentSelector m_selector;
80
81     /**
82      * The role that this selector was aquired via.
83      */
84     private final String JavaDoc m_key;
85
86     /**
87      * This constructor is a constructor for a ComponentServiceManager
88      *
89      * @param key the key used to aquire this selector
90      * @param selector the selector to wrap
91      */
92     public WrapperServiceSelector( final String JavaDoc key,
93                                    final ComponentSelector selector )
94     {
95         if( null == key )
96         {
97             throw new NullPointerException JavaDoc( "key" );
98         }
99         if( null == selector )
100         {
101             throw new NullPointerException JavaDoc( "selector" );
102         }
103
104         m_key = key + "/";
105         m_selector = selector;
106     }
107
108     /**
109      * Select a service based on a policy.
110      *
111      * @param policy the policy
112      * @return the service
113      * @throws ServiceException if unable to select service
114      */
115     public Object JavaDoc select( final Object JavaDoc policy )
116         throws ServiceException
117     {
118         try
119         {
120             return m_selector.select( policy );
121         }
122         catch( final ComponentException ce )
123         {
124             throw new ServiceException( m_key + policy, ce.getMessage(), ce );
125         }
126     }
127
128     /**
129      * Check to see if a {@link Object} exists relative to the supplied policy.
130      *
131      * @param policy a {@link Object} containing the selection criteria
132      * @return True if the component is available, False if it not.
133      */
134     public boolean isSelectable( final Object JavaDoc policy )
135     {
136         return m_selector.hasComponent( policy );
137     }
138
139     /**
140      * Return the {@link Object} when you are finished with it. This
141      * allows the {@link ServiceSelector} to handle the End-Of-Life Lifecycle
142      * events associated with the {@link Object}. Please note, that no
143      * Exception should be thrown at this point. This is to allow easy use of the
144      * ServiceSelector system without having to trap Exceptions on a release.
145      *
146      * @param object The {@link Object} we are releasing.
147      */
148     public void release( Object JavaDoc object )
149     {
150         m_selector.release( (Component)object );
151     }
152
153     /**
154      * The {@link WrapperServiceManager} wraps ComponentSelectors in
155      * WrapperServiceSelectors when they are looked up. This method
156      * makes it possible to release the original component selector.
157      *
158      * @return The {@link ComponentSelector} being wrapped.
159      */
160     ComponentSelector getWrappedSelector()
161     {
162         return m_selector;
163     }
164 }
165
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