1 package org.apache.commons.digester3.plugins;
2
3 /*
4 * Licensed to the Apache Software Foundation (ASF) under one
5 * or more contributor license agreements. See the NOTICE file
6 * distributed with this work for additional information
7 * regarding copyright ownership. The ASF licenses this file
8 * to you under the Apache License, Version 2.0 (the
9 * "License"); you may not use this file except in compliance
10 * with the License. You may obtain a copy of the License at
11 *
12 * http://www.apache.org/licenses/LICENSE-2.0
13 *
14 * Unless required by applicable law or agreed to in writing,
15 * software distributed under the License is distributed on an
16 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
17 * KIND, either express or implied. See the License for the
18 * specific language governing permissions and limitations
19 * under the License.
20 */
21
22 import java.util.Properties;
23
24 import org.apache.commons.digester3.Digester;
25
26 /**
27 * Each concrete implementation of RuleFinder is an algorithm for locating a source of digester rules for a plugin. The
28 * algorithm may use info explicitly provided by the user as part of the plugin declaration, or not (in which case the
29 * concrete RuleFinder subclass typically has Dflt as part of its name).
30 * <p>
31 * Instances of this class can also be regarded as a Factory for RuleLoaders, except that an instance of a RuleLoader is
32 * only created if the particular finder algorithm can locate a suitable source of rules given the plugin class and
33 * associated properties.
34 * <p>
35 * This is an abstract class rather than an interface in order to make it possible to enhance this class in future
36 * without breaking binary compatibility; it is possible to add methods to an abstract class, but not to an interface.
37 *
38 * @since 1.6
39 */
40 public abstract class RuleFinder
41 {
42
43 /**
44 * Apply the finder algorithm to attempt to locate a source of digester rules for the specified plugin class.
45 * <p>
46 * This method is invoked when a plugin is declared by the user, either via an explicit use of
47 * PluginDeclarationRule, or implicitly via an "inline declaration" where the declaration and use are simultaneous.
48 * <p>
49 * If dynamic rules for the specified plugin class are located, then the RuleFinder will return a RuleLoader object
50 * encapsulating those rules, and this object will be invoked each time the user actually requests an instance of
51 * the declared plugin class, to load the custom rules associated with that plugin instance.
52 * <p>
53 * If no dynamic rules can be found, null is returned. This is not an error; merely an indication that this
54 * particular algorithm found no matches.
55 * <p>
56 * The properties object holds any xml attributes the user may have specified on the plugin declaration in order to
57 * indicate how to locate the plugin rules.
58 * <p>
59 *
60 * @param d The digester instance where locating plugin classes
61 * @param pluginClass The plugin Java class
62 * @param p The properties object that holds any xml attributes the user may have specified on the plugin
63 * declaration in order to indicate how to locate the plugin rules.
64 * @return a source of digester rules for the specified plugin class.
65 * @throws PluginException if the algorithm finds a source of rules, but there is something invalid
66 * about that source.
67 */
68 public abstract RuleLoader findLoader( Digester d, Class<?> pluginClass, Properties p )
69 throws PluginException;
70
71 }