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Java > Open Source Codes > org > apache > avalon > framework > component > WrapperComponentSelector


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55
56 package org.apache.avalon.framework.component;
57
58 import org.apache.avalon.framework.service.ServiceSelector;
59 import org.apache.avalon.framework.service.ServiceException;
60
61 /**
62  * This is a {@link ServiceSelector} implementation that can wrap around a legacy
63  * {@link ComponentSelector} object effectively adapting a {@link ComponentSelector}
64  * interface to a {@link ServiceSelector} interface.
65  *
66  * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
67  * @version CVS $Revision: 1.8 $ $Date: 2003/02/11 07:13:45 $
68  */

69 public class WrapperComponentSelector
70     implements ComponentSelector
71 {
72     /**
73      * The Selector we are wrapping.
74      */

75     private final ServiceSelector m_selector;
76
77     /**
78      * The role that this selector was aquired via.
79      */

80     private final String JavaDoc m_key;
81
82     /**
83      * This constructor is a constructor for a WrapperComponentSelector.
84      *
85      * @param key the key used to aquire this selector
86      * @param selector the selector to wrap
87      */

88     public WrapperComponentSelector( final String JavaDoc key,
89                                      final ServiceSelector selector )
90     {
91         if( null == key )
92         {
93             throw new NullPointerException JavaDoc( "key" );
94         }
95         if( null == selector )
96         {
97             throw new NullPointerException JavaDoc( "selector" );
98         }
99
100         m_key = key + "/";
101         m_selector = selector;
102     }
103
104     /**
105      * Select a Component based on a policy.
106      *
107      * @param policy the policy
108      * @return the Component
109      * @throws ComponentException if unable to select service
110      */

111     public Component select( final Object JavaDoc policy )
112         throws ComponentException
113     {
114         try
115         {
116             final Object JavaDoc object = m_selector.select( policy );
117             if( object instanceof Component )
118             {
119                 return (Component)object;
120             }
121         }
122         catch( final ServiceException se )
123         {
124             throw new ComponentException( m_key + policy, se.getMessage(), se );
125         }
126
127         final String JavaDoc message = "Role does not implement the Component "
128            + "interface and thus can not be accessed via ComponentSelector";
129         throw new ComponentException( m_key + policy, message );
130     }
131
132     /**
133      * Check to see if a {@link Component} exists relative to the supplied policy.
134      *
135      * @param policy a {@link Object} containing the selection criteria
136      * @return True if the component is available, False if it not.
137      */

138     public boolean hasComponent( final Object JavaDoc policy )
139     {
140         return m_selector.isSelectable( policy );
141     }
142
143     /**
144      * Return the {@link Object} when you are finished with it. This
145      * allows the {@link ServiceSelector} to handle the End-Of-Life Lifecycle
146      * events associated with the {@link Object}. Please note, that no
147      * Exception should be thrown at this point. This is to allow easy use of the
148      * ServiceSelector system without having to trap Exceptions on a release.
149      *
150      * @param object The {@link Object} we are releasing.
151      */

152     public void release( final Component object )
153     {
154         m_selector.release( object );
155     }
156
157     /**
158      * The {@link WrapperComponentManager} wraps ServiceSelectors in
159      * WrapperServiceSelectors when they are looked up. This method
160      * makes it possible to release the original component selector.
161      *
162      * @return The {@link ServiceSelector} being wrapped.
163      */

164     ServiceSelector getWrappedSelector()
165     {
166         return m_selector;
167     }
168 }
169
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