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Java > Open Source Codes > org > apache > avalon > meta > info > ContextDescriptor


1 /*
2
3  ============================================================================
4                    The Apache Software License, Version 1.1
5  ============================================================================
6
7  Copyright (C) 1999-2002 The Apache Software Foundation. All rights reserved.
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9  Redistribution and use in source and binary forms, with or without modifica-
10  tion, are permitted provided that the following conditions are met:
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12  1. Redistributions of source code must retain the above copyright notice,
13     this list of conditions and the following disclaimer.
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23     and wherever such third-party acknowledgments normally appear.
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25  4. The names "Jakarta", "Apache Avalon", "Avalon Framework" and
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49 */
50
51 package org.apache.avalon.meta.info;
52
53 import java.util.ArrayList JavaDoc;
54 import java.util.Arrays JavaDoc;
55 import java.util.List JavaDoc;
56 import java.util.Properties JavaDoc;
57
58 /**
59  * A descriptor describing the Context that the Component
60  * is passed to describe information about Runtime environment
61  * of Component. It contains information such as;
62  * <ul>
63  * <li>classname: the classname of the Context type if it
64  * differs from base Context class (ie BlockContext).</li>
65  * <li>entries: a list of entries contained in context</li>
66  * </ul>
67  *
68  * <p>Also associated with each Context is a set of arbitrary
69  * attributes that can be used to store extra information
70  * about Context requirements.</p>
71  *
72  * @author <a HREF="mailto:dev@avalon.apache.org">Avalon Development Team</a>
73  * @version $Revision: 1.9 $ $Date: 2003/09/09 22:00:42 $
74  */
75 public class ContextDescriptor extends Descriptor
76 {
77     //---------------------------------------------------------
78 // static
79 //---------------------------------------------------------
80
81    /**
82     * The context entry key for accessing a component name.
83     */
84     public static final String JavaDoc NAME_KEY =
85             "urn:avalon:name";
86
87    /**
88     * The context entry key for accessing a component partition name.
89     */
90     public static final String JavaDoc PARTITION_KEY =
91             "urn:avalon:partition";
92
93    /**
94     * The context entry key for accessing a component home directory.
95     */
96     public static final String JavaDoc HOME_KEY =
97             "urn:avalon:home";
98
99    /**
100     * The context entry key for accessing a component temporary directory.
101     */
102     public static final String JavaDoc TEMP_KEY =
103             "urn:avalon:temp";
104
105    /**
106     * The context entry key for accessing a component classloader.
107     */
108     public static final String JavaDoc CLASSLOADER_KEY =
109             "urn:avalon:classloader";
110
111    /**
112     * Context attribute key used to declare a custom contextualization
113     * interface.
114     */
115     public static final String JavaDoc STRATEGY_KEY =
116             "urn:avalon:context.strategy";
117
118    /**
119     * Context interface classname.
120     */
121     public static final String JavaDoc AVALON_CONTEXT_CLASSNAME =
122             "org.apache.avalon.framework.context.Context";
123
124     //---------------------------------------------------------
125 // immutable state
126 //---------------------------------------------------------
127
128     private final String JavaDoc m_classname;
129
130     private final EntryDescriptor[] m_entries;
131
132     //---------------------------------------------------------
133 // constructors
134 //---------------------------------------------------------
135
136     /**
137      * Create a standard descriptor without attributes.
138      * @param entries the set of entries required within the context
139      */
140     public ContextDescriptor( final EntryDescriptor[] entries )
141     {
142         this( null, entries, null );
143     }
144
145     /**
146      * Create a descriptor without attributes.
147      * @param classname the classname of a castable interface
148      * @param entries the set of entries required within the context
149      */
150     public ContextDescriptor( final String JavaDoc classname,
151                               final EntryDescriptor[] entries )
152     {
153         this( classname, entries, null );
154     }
155
156     /**
157      * Create a descriptor.
158      * @param classname the classname of a castable interface
159      * @param entries the set of entries required within the context
160      * @param attributes supplimentary attributes associated with the context
161      * @exception NullPointerException if the entries argument is null
162      */
163     public ContextDescriptor( final String JavaDoc classname,
164                               final EntryDescriptor[] entries,
165                               final Properties JavaDoc attributes )
166             throws NullPointerException JavaDoc, IllegalArgumentException JavaDoc
167     {
168         super( attributes );
169
170         if ( null == entries )
171         {
172             throw new NullPointerException JavaDoc( "entries" );
173         }
174
175         if ( null == classname )
176         {
177             m_classname = AVALON_CONTEXT_CLASSNAME;
178         }
179         else
180         {
181             m_classname = classname;
182         }
183         m_entries = entries;
184     }
185
186     //---------------------------------------------------------
187 // implementation
188 //---------------------------------------------------------
189
190     /**
191      * Return the classname of the context
192      * object interface that the supplied context argument
193      * supports under a type-safe cast.
194      *
195      * @return the reference descriptor.
196      */
197     public String JavaDoc getContextInterfaceClassname()
198     {
199         return m_classname;
200     }
201
202     /**
203      * Return the local entries contained in the context.
204      *
205      * @return the entries contained in the context.
206      */
207     public EntryDescriptor[] getEntries()
208     {
209         return m_entries;
210     }
211
212     /**
213      * Return the entry with specified alias. If the entry
214      * does not declare an alias the method will return an
215      * entry with the matching key.
216      *
217      * @param alias the context entry key to lookup
218      * @return the entry with specified key.
219      */
220     public EntryDescriptor getEntry( final String JavaDoc alias )
221     {
222         if ( null == alias )
223         {
224             throw new NullPointerException JavaDoc( "alias" );
225         }
226
227         for ( int i = 0; i < m_entries.length; i++ )
228         {
229             final EntryDescriptor entry = m_entries[i];
230             if( entry.getAlias().equals( alias ) )
231             {
232                 return entry;
233             }
234         }
235
236         for ( int i = 0; i < m_entries.length; i++ )
237         {
238             final EntryDescriptor entry = m_entries[i];
239             if( entry.getKey().equals( alias ) )
240             {
241                 return entry;
242             }
243         }
244
245         return null;
246     }
247
248     /**
249      * Returns a set of entry descriptors resulting from a merge of the descriptors
250      * container in this descriptor with the supplied descriptors.
251      *
252      * @param entries the entries to merge
253      * @return the mergerged set of entries
254      * @exception IllegalArgumentException if a entry conflict occurs
255      */
256     public EntryDescriptor[] merge( EntryDescriptor[] entries )
257             throws IllegalArgumentException JavaDoc
258     {
259         for ( int i = 0; i < entries.length; i++ )
260         {
261             EntryDescriptor entry = entries[i];
262             final String JavaDoc key = entry.getKey();
263             EntryDescriptor local = getEntry( entry.getKey() );
264             if ( local != null )
265             {
266                 if ( !entry.getClassname().equals( local.getClassname() ) )
267                 {
268                     final String JavaDoc error =
269                             "Conflicting entry type for key: " + key;
270                     throw new IllegalArgumentException JavaDoc( error );
271                 }
272             }
273         }
274
275         return join( entries, getEntries() );
276     }
277
278     private EntryDescriptor[] join( EntryDescriptor[] primary, EntryDescriptor[] secondary )
279     {
280         List JavaDoc list = new ArrayList JavaDoc( primary.length + secondary.length );
281         list.addAll( Arrays.asList( primary ) );
282         list.addAll( Arrays.asList( secondary ) );
283         return (EntryDescriptor[]) list.toArray( new EntryDescriptor[0] );
284     }
285
286    /**
287     * Test is the supplied object is equal to this object.
288     * @return true if the object are equivalent
289     */
290     public boolean equals( Object JavaDoc other )
291     {
292         boolean isEqual = super.equals( other );
293         if( isEqual ) isEqual = other instanceof ContextDescriptor;
294         if( isEqual )
295         {
296             ContextDescriptor entity = (ContextDescriptor) other;
297             isEqual = isEqual && m_classname.equals( entity.m_classname );
298             for( int i=0; i<m_entries.length; i++ )
299             {
300                 isEqual = isEqual && m_entries[i].equals( entity.m_entries[i] );
301             }
302         }
303         return isEqual;
304     }
305
306    /**
307     * Return the hashcode for the object.
308     * @return the hashcode value
309     */
310     public int hashCode()
311     {
312         int hash = super.hashCode();
313         hash >>>= 7;
314         hash ^= m_classname.hashCode();
315         for( int i=0; i<m_entries.length; i++ )
316         {
317             hash >>>= 7;
318             hash ^= m_entries[i].hashCode();
319         }
320         return hash;
321     }
322 }
323
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