Loader


1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    * 
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  
18  
19  package org.apache.catalina;
20  
21  
22  import java.beans.PropertyChangeListener  ;
23  
24  
25  /**
26   * A <b>Loader</b> represents a Java ClassLoader implementation that can
27   * be used by a Container to load class files (within a repository associated
28   * with the Loader) that are designed to be reloaded upon request, as well as
29   * a mechanism to detect whether changes have occurred in the underlying
30   * repository.
31   * <p>
32   * In order for a <code>Loader</code> implementation to successfully operate
33   * with a <code>Context</code> implementation that implements reloading, it
34   * must obey the following constraints:
35   * <ul>
36   * <li>Must implement <code>Lifecycle</code> so that the Context can indicate
37   *     that a new class loader is required.
38   * <li>The <code>start()</code> method must unconditionally create a new
39   *     <code>ClassLoader</code> implementation.
40   * <li>The <code>stop()</code> method must throw away its reference to the
41   *     <code>ClassLoader</code> previously utilized, so that the class loader,
42   *     all classes loaded by it, and all objects of those classes, can be
43   *     garbage collected.
44   * <li>Must allow a call to <code>stop()</code> to be followed by a call to
45   *     <code>start()</code> on the same <code>Loader</code> instance.
46   * <li>Based on a policy chosen by the implementation, must call the
47   *     <code>Context.reload()</code> method on the owning <code>Context</code>
48   *     when a change to one or more of the class files loaded by this class
49   *     loader is detected.
50   * </ul>
51   *
52   * @author Craig R. McClanahan
53   * @version $Revision: 467222 $ $Date: 2006-10-24 05:17:11 +0200 (mar., 24 oct. 2006) $
54   */
55  
56  public interface Loader {
57  
58  
59      // ------------------------------------------------------------- Properties
60  
61  
62      /**
63       * Execute a periodic task, such as reloading, etc. This method will be
64       * invoked inside the classloading context of this container. Unexpected
65       * throwables will be caught and logged.
66       */
67      public void backgroundProcess();
68  
69  
70      /**
71       * Return the Java class loader to be used by this Container.
72       */
73      public ClassLoader   getClassLoader();
74  
75  
76      /**
77       * Return the Container with which this Loader has been associated.
78       */
79      public Container getContainer();
80  
81  
82      /**
83       * Set the Container with which this Loader has been associated.
84       *
85       * @param container The associated Container
86       */
87      public void setContainer(Container container);
88  
89  
90      /**
91       * Return the "follow standard delegation model" flag used to configure
92       * our ClassLoader.
93       */
94      public boolean getDelegate();
95  
96  
97      /**
98       * Set the "follow standard delegation model" flag used to configure
99       * our ClassLoader.
100      *
101      * @param delegate The new flag
102      */
103     public void setDelegate(boolean delegate);
104 
105 
106     /**
107      * Return descriptive information about this Loader implementation and
108      * the corresponding version number, in the format
109      * <code>&lt;description&gt;/&lt;version&gt;</code>.
110      */
111     public String   getInfo();
112 
113 
114     /**
115      * Return the reloadable flag for this Loader.
116      */
117     public boolean getReloadable();
118 
119 
120     /**
121      * Set the reloadable flag for this Loader.
122      *
123      * @param reloadable The new reloadable flag
124      */
125     public void setReloadable(boolean reloadable);
126 
127 
128     // --------------------------------------------------------- Public Methods
129 
130 
131     /**
132      * Add a property change listener to this component.
133      *
134      * @param listener The listener to add
135      */
136     public void addPropertyChangeListener(PropertyChangeListener   listener);
137 
138 
139     /**
140      * Add a new repository to the set of repositories for this class loader.
141      *
142      * @param repository Repository to be added
143      */
144     public void addRepository(String   repository);
145 
146 
147     /**
148      * Return the set of repositories defined for this class loader.
149      * If none are defined, a zero-length array is returned.
150      */
151     public String  [] findRepositories();
152 
153 
154     /**
155      * Has the internal repository associated with this Loader been modified,
156      * such that the loaded classes should be reloaded?
157      */
158     public boolean modified();
159 
160 
161     /**
162      * Remove a property change listener from this component.
163      *
164      * @param listener The listener to remove
165      */
166     public void removePropertyChangeListener(PropertyChangeListener   listener);
167 
168 
169 }
170
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