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 * https://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 package org.apache.commons.configuration2;
18
19 import java.util.Collection;
20 import java.util.List;
21
22 import org.apache.commons.configuration2.tree.ExpressionEngine;
23 import org.apache.commons.configuration2.tree.NodeModelSupport;
24
25 /**
26 * <p>
27 * An interface for mutable hierarchical configurations.
28 * </p>
29 * <p>
30 * This interface introduces methods for manipulating tree-like structured configuration sources. Also, all methods
31 * defined by the {@code Configuration} interface are available.
32 * </p>
33 * <p>
34 * This interface does not make any assumptions about the concrete type of nodes used by an implementation; this is
35 * reflected by a generic type parameter. Concrete implementations may therefore define their own hierarchical
36 * structures.
37 * </p>
38 *
39 * @param <T> the type of the nodes used by this hierarchical configuration
40 * @since 2.0
41 */
42 public interface HierarchicalConfiguration<T> extends Configuration, ImmutableHierarchicalConfiguration, NodeModelSupport<T> {
43 /**
44 * Adds a collection of nodes at the specified position of the configuration tree. This method works similar to
45 * {@code addProperty()}, but instead of a single property a whole collection of nodes can be added - and thus complete
46 * configuration sub trees. E.g. with this method it is possible to add parts of another
47 * {@code BaseHierarchicalConfiguration} object to this object. If the passed in key refers to an existing and unique
48 * node, the new nodes are added to this node. Otherwise a new node will be created at the specified position in the
49 * hierarchy.
50 *
51 * @param key the key where the nodes are to be added; can be <strong>null </strong>, then they are added to the root node
52 * @param nodes a collection with the {@code Node} objects to be added
53 */
54 void addNodes(String key, Collection<? extends T> nodes);
55
56 /**
57 * Returns a list with sub configurations for all child nodes of the node selected by the given key. This method works
58 * like {@link #immutableChildConfigurationsAt(String)}, but returns a list with mutable configuration objects. The
59 * configuration objects returned are <strong>not</strong> connected to the parent configuration.
60 *
61 * @param key the key for selecting the desired parent node
62 * @return a collection with {@code HierarchicalConfiguration} objects for all child nodes of the selected parent node
63 */
64 List<HierarchicalConfiguration<T>> childConfigurationsAt(String key);
65
66 /**
67 * Returns a list with sub configurations for all child nodes of the node selected by the given key allowing the caller
68 * to specify the {@code supportUpdates} flag.
69 *
70 * @param key the key for selecting the desired parent node
71 * @param supportUpdates a flag whether the returned sub configuration should be directly connected to its parent
72 * @return a collection with {@code HierarchicalConfiguration} objects for all child nodes of the selected parent node
73 */
74 List<HierarchicalConfiguration<T>> childConfigurationsAt(String key, boolean supportUpdates);
75
76 /**
77 * Removes all values of the property with the given name and of keys that start with this name. So if there is a
78 * property with the key "foo" and a property with the key "foo.bar", a call of
79 * {@code clearTree("foo")} would remove both properties.
80 *
81 * @param key the key of the property to be removed
82 */
83 void clearTree(String key);
84
85 /**
86 * Returns a hierarchical subnode configuration for the node specified by the given key. This is a short form for
87 * {@code configurationAt(key,
88 * <strong>false</strong>)}.
89 *
90 * @param key the key that selects the sub tree
91 * @return a hierarchical configuration that contains this sub tree
92 * @see SubnodeConfiguration
93 */
94 HierarchicalConfiguration<T> configurationAt(String key);
95
96 /**
97 * <p>
98 * Returns a hierarchical sub configuration object that wraps the configuration node specified by the given key. This
99 * method provides an easy means of accessing sub trees of a hierarchical configuration. In the returned configuration
100 * the sub tree can directly be accessed, it becomes the root node of this configuration. Because of this the passed in
101 * key must select exactly one configuration node; otherwise an {@code IllegalArgumentException} will be thrown.
102 * </p>
103 * <p>
104 * The difference between this method and the {@link #subset(String)} method is that {@code subset()} supports arbitrary
105 * subsets of configuration nodes while {@code configurationAt()} only returns a single sub tree. Please refer to the
106 * documentation of the {@link SubnodeConfiguration} class to obtain further information about sub configurations and
107 * when they should be used.
108 * </p>
109 * <p>
110 * With the {@code supportUpdate} flag the behavior of the returned sub configuration regarding updates of its parent
111 * configuration can be determined. If set to <strong>false</strong>, the configurations return on independent nodes structures.
112 * So changes made on one configuration cannot be seen by the other one. A value of <strong>true</strong> in contrast creates a
113 * direct connection between both configurations - they are then using the same underlying data structures as much as
114 * possible. There are however changes which break this connection; for instance, if the sub tree the sub configuration
115 * belongs to is completely removed from the parent configuration. If such a change happens, the sub configuration
116 * becomes detached from its parent. It can still be used in a normal way, but changes on it are not reflected by the
117 * parent and vice verse. Also, it is not possible to reattach a once detached sub configuration.
118 * </p>
119 *
120 * @param key the key that selects the sub tree
121 * @param supportUpdates a flag whether the returned sub configuration should be directly connected to its parent
122 * @return a hierarchical configuration that contains this sub tree
123 * @see SubnodeConfiguration
124 */
125 HierarchicalConfiguration<T> configurationAt(String key, boolean supportUpdates);
126
127 /**
128 * Returns a list of sub configurations for all configuration nodes selected by the given key. This method will evaluate
129 * the passed in key (using the current {@code ExpressionEngine}) and then create a sub configuration for each returned
130 * node (like {@link #configurationAt(String)} ). This is especially useful when dealing with list-like structures. As
131 * an example consider the configuration that contains data about database tables and their fields. If you need access
132 * to all fields of a certain table, you can simply do
133 *
134 * <pre>
135 * List fields = config.configurationsAt("tables.table(0).fields.field");
136 * for(Iterator it = fields.iterator(); it.hasNext();)
137 * {
138 * BaseHierarchicalConfiguration sub = (BaseHierarchicalConfiguration) it.next();
139 * // now the children and attributes of the field node can be
140 * // directly accessed
141 * String fieldName = sub.getString("name");
142 * String fieldType = sub.getString("type");
143 * ...
144 * </pre>
145 *
146 * The configuration objects returned are <strong>not</strong> connected to the parent configuration.
147 *
148 * @param key the key for selecting the desired nodes
149 * @return a list with hierarchical configuration objects; each configuration represents one of the nodes selected by
150 * the passed in key
151 */
152 List<HierarchicalConfiguration<T>> configurationsAt(String key);
153
154 /**
155 * Returns a list of sub configurations for all configuration nodes selected by the given key allowing the caller to
156 * specify the {@code supportUpdates} flag. This method works like {@link #configurationsAt(String)}, but with the
157 * additional boolean parameter it can be specified whether the returned configurations react on updates of the parent
158 * configuration.
159 *
160 * @param key the key for selecting the desired nodes
161 * @param supportUpdates a flag whether the returned sub configuration should be directly connected to its parent
162 * @return a list with hierarchical configuration objects; each configuration represents one of the nodes selected by
163 * the passed in key
164 * @see #configurationsAt(String, boolean)
165 */
166 List<HierarchicalConfiguration<T>> configurationsAt(String key, boolean supportUpdates);
167
168 /**
169 * Sets the expression engine to be used by this configuration. All property keys this configuration has to deal with
170 * will be interpreted by this engine.
171 *
172 * @param expressionEngine the new expression engine; can be <strong>null</strong>, then the default expression engine will be
173 * used
174 */
175 void setExpressionEngine(ExpressionEngine expressionEngine);
176 }