KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > org > apache > commons > chain > CatalogFactory


1 /*
2  * Copyright 1999-2004 The Apache Software Foundation
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.chain;
17
18 import java.util.HashMap JavaDoc;
19 import java.util.Iterator JavaDoc;
20 import java.util.Map JavaDoc;
21 import org.apache.commons.chain.impl.CatalogFactoryBase;
22
23 /**
24  * <p>A {@link CatalogFactory} is a class used to store and retrieve
25  * {@link Catalog}s. The factory allows for a default {@link Catalog}
26  * as well as {@link Catalog}s stored with a name key. Follows the
27  * Factory pattern (see GoF).</p>
28  *
29  * @author Sean Schofield
30  * @version $Revision: 1.5 $ $Date: 2004/11/30 05:52:22 $
31  */
32
33 public abstract class CatalogFactory {
34
35
36     // --------------------------------------------------------- Public Methods
37
38
39     /**
40      * <p>Gets the default instance of Catalog associated with the factory
41      * (if any); otherwise, return <code>null</code>.</p>
42      *
43      * @return the default Catalog instance
44      */
45     public abstract Catalog getCatalog();
46
47
48     /**
49      * <p>Sets the default instance of Catalog associated with the factory.</p>
50      *
51      * @param catalog the default Catalog instance
52      */
53     public abstract void setCatalog(Catalog catalog);
54
55
56     /**
57      * <p>Retrieves a Catalog instance by name (if any); otherwise
58      * return <code>null</code>.</p>
59      *
60      * @param name the name of the Catalog to retrieve
61      * @return the specified Catalog
62      */
63     public abstract Catalog getCatalog(String JavaDoc name);
64
65
66     /**
67      * <p>Adds a named instance of Catalog to the factory (for subsequent
68      * retrieval later).</p>
69      *
70      * @param name the name of the Catalog to add
71      * @param catalog the Catalog to add
72      */
73     public abstract void addCatalog(String JavaDoc name, Catalog catalog);
74
75
76     /**
77      * <p>Return an <code>Iterator</code> over the set of named
78      * {@link Catalog}s known to this {@link CatalogFactory}.
79      * If there are no known catalogs, an empty Iterator is returned.</p>
80      */
81     public abstract Iterator JavaDoc getNames();
82
83
84     // ------------------------------------------------------- Static Variables
85
86
87     /**
88      * <p>The set of registered {@link CatalogFactory} instances,
89      * keyed by the relevant class loader.</p>
90      */
91     private static Map JavaDoc factories = new HashMap JavaDoc();
92
93
94     // -------------------------------------------------------- Static Methods
95
96
97     /**
98      * <p>Return the singleton {@link CatalogFactory} instance
99      * for the relevant <code>ClassLoader</code>. For applications
100      * that use a thread context class loader (such as web applications
101      * running inside a servet container), this will return a separate
102      * instance for each application, even if this class is loaded from
103      * a shared parent class loader.</p>
104      *
105      * @return the per-application singleton instance of {@link CatalogFactory}
106      */
107     public static CatalogFactory getInstance() {
108
109         CatalogFactory factory = null;
110         ClassLoader JavaDoc cl = getClassLoader();
111         synchronized (factories) {
112             factory = (CatalogFactory) factories.get(cl);
113             if (factory == null) {
114                 factory = new CatalogFactoryBase();
115                 factories.put(cl, factory);
116             }
117         }
118         return factory;
119
120     }
121
122
123     /**
124      * <p>Clear all references to registered catalogs, as well as to the
125      * relevant class loader. This method should be called, for example,
126      * when a web application utilizing this class is removed from
127      * service, to allow for garbage collection.</p>
128      */
129     public static void clear() {
130
131         synchronized (factories) {
132             factories.remove(getClassLoader());
133         }
134
135     }
136
137
138     // ------------------------------------------------------- Private Methods
139
140
141     /**
142      * <p>Return the relevant <code>ClassLoader</code> to use as a Map key
143      * for this request. If there is a thread context class loader, return
144      * that; otherwise, return the class loader that loaded this class.</p>
145      */
146     private static ClassLoader JavaDoc getClassLoader() {
147
148         ClassLoader JavaDoc cl = Thread.currentThread().getContextClassLoader();
149         if (cl == null) {
150             cl = CatalogFactory.class.getClassLoader();
151         }
152         return cl;
153
154     }
155
156
157 }
158
Popular Tags