001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *     http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.configuration2;
018
019import java.util.Collection;
020import java.util.List;
021
022import org.apache.commons.configuration2.tree.ExpressionEngine;
023import org.apache.commons.configuration2.tree.NodeModelSupport;
024
025/**
026 * <p>
027 * An interface for mutable hierarchical configurations.
028 * </p>
029 * <p>
030 * This interface introduces methods for manipulating tree-like structured configuration sources. Also, all methods
031 * defined by the {@code Configuration} interface are available.
032 * </p>
033 * <p>
034 * This interface does not make any assumptions about the concrete type of nodes used by an implementation; this is
035 * reflected by a generic type parameter. Concrete implementations may therefore define their own hierarchical
036 * structures.
037 * </p>
038 *
039 * @since 2.0
040 * @param <T> the type of the nodes used by this hierarchical configuration
041 */
042public interface HierarchicalConfiguration<T> extends Configuration, ImmutableHierarchicalConfiguration, NodeModelSupport<T> {
043    /**
044     * Sets the expression engine to be used by this configuration. All property keys this configuration has to deal with
045     * will be interpreted by this engine.
046     *
047     * @param expressionEngine the new expression engine; can be <b>null</b>, then the default expression engine will be
048     *        used
049     */
050    void setExpressionEngine(ExpressionEngine expressionEngine);
051
052    /**
053     * Adds a collection of nodes at the specified position of the configuration tree. This method works similar to
054     * {@code addProperty()}, but instead of a single property a whole collection of nodes can be added - and thus complete
055     * configuration sub trees. E.g. with this method it is possible to add parts of another
056     * {@code BaseHierarchicalConfiguration} object to this object. If the passed in key refers to an existing and unique
057     * node, the new nodes are added to this node. Otherwise a new node will be created at the specified position in the
058     * hierarchy.
059     *
060     * @param key the key where the nodes are to be added; can be <b>null </b>, then they are added to the root node
061     * @param nodes a collection with the {@code Node} objects to be added
062     */
063    void addNodes(String key, Collection<? extends T> nodes);
064
065    /**
066     * <p>
067     * Returns a hierarchical sub configuration object that wraps the configuration node specified by the given key. This
068     * method provides an easy means of accessing sub trees of a hierarchical configuration. In the returned configuration
069     * the sub tree can directly be accessed, it becomes the root node of this configuration. Because of this the passed in
070     * key must select exactly one configuration node; otherwise an {@code IllegalArgumentException} will be thrown.
071     * </p>
072     * <p>
073     * The difference between this method and the {@link #subset(String)} method is that {@code subset()} supports arbitrary
074     * subsets of configuration nodes while {@code configurationAt()} only returns a single sub tree. Please refer to the
075     * documentation of the {@link SubnodeConfiguration} class to obtain further information about sub configurations and
076     * when they should be used.
077     * </p>
078     * <p>
079     * With the {@code supportUpdate} flag the behavior of the returned sub configuration regarding updates of its parent
080     * configuration can be determined. If set to <b>false</b>, the configurations return on independent nodes structures.
081     * So changes made on one configuration cannot be seen by the other one. A value of <b>true</b> in contrast creates a
082     * direct connection between both configurations - they are then using the same underlying data structures as much as
083     * possible. There are however changes which break this connection; for instance, if the sub tree the sub configuration
084     * belongs to is completely removed from the parent configuration. If such a change happens, the sub configuration
085     * becomes detached from its parent. It can still be used in a normal way, but changes on it are not reflected by the
086     * parent and vice verse. Also, it is not possible to reattach a once detached sub configuration.
087     * </p>
088     *
089     * @param key the key that selects the sub tree
090     * @param supportUpdates a flag whether the returned sub configuration should be directly connected to its parent
091     * @return a hierarchical configuration that contains this sub tree
092     * @see SubnodeConfiguration
093     */
094    HierarchicalConfiguration<T> configurationAt(String key, boolean supportUpdates);
095
096    /**
097     * Returns a hierarchical subnode configuration for the node specified by the given key. This is a short form for
098     * {@code configurationAt(key,
099     * <b>false</b>)}.
100     *
101     * @param key the key that selects the sub tree
102     * @return a hierarchical configuration that contains this sub tree
103     * @see SubnodeConfiguration
104     */
105    HierarchicalConfiguration<T> configurationAt(String key);
106
107    /**
108     * Returns a list of sub configurations for all configuration nodes selected by the given key. This method will evaluate
109     * the passed in key (using the current {@code ExpressionEngine}) and then create a sub configuration for each returned
110     * node (like {@link #configurationAt(String)} ). This is especially useful when dealing with list-like structures. As
111     * an example consider the configuration that contains data about database tables and their fields. If you need access
112     * to all fields of a certain table, you can simply do
113     *
114     * <pre>
115     * List fields = config.configurationsAt("tables.table(0).fields.field");
116     * for(Iterator it = fields.iterator(); it.hasNext();)
117     * {
118     *     BaseHierarchicalConfiguration sub = (BaseHierarchicalConfiguration) it.next();
119     *     // now the children and attributes of the field node can be
120     *     // directly accessed
121     *     String fieldName = sub.getString("name");
122     *     String fieldType = sub.getString("type");
123     *     ...
124     * </pre>
125     *
126     * The configuration objects returned are <strong>not</strong> connected to the parent configuration.
127     *
128     * @param key the key for selecting the desired nodes
129     * @return a list with hierarchical configuration objects; each configuration represents one of the nodes selected by
130     *         the passed in key
131     */
132    List<HierarchicalConfiguration<T>> configurationsAt(String key);
133
134    /**
135     * Returns a list of sub configurations for all configuration nodes selected by the given key allowing the caller to
136     * specify the {@code supportUpdates} flag. This method works like {@link #configurationsAt(String)}, but with the
137     * additional boolean parameter it can be specified whether the returned configurations react on updates of the parent
138     * configuration.
139     *
140     * @param key the key for selecting the desired nodes
141     * @param supportUpdates a flag whether the returned sub configuration should be directly connected to its parent
142     * @return a list with hierarchical configuration objects; each configuration represents one of the nodes selected by
143     *         the passed in key
144     * @see #configurationsAt(String, boolean)
145     */
146    List<HierarchicalConfiguration<T>> configurationsAt(String key, boolean supportUpdates);
147
148    /**
149     * Returns a list with sub configurations for all child nodes of the node selected by the given key. This method works
150     * like {@link #immutableChildConfigurationsAt(String)}, but returns a list with mutable configuration objects. The
151     * configuration objects returned are <strong>not</strong> connected to the parent configuration.
152     *
153     * @param key the key for selecting the desired parent node
154     * @return a collection with {@code HierarchicalConfiguration} objects for all child nodes of the selected parent node
155     */
156    List<HierarchicalConfiguration<T>> childConfigurationsAt(String key);
157
158    /**
159     * Returns a list with sub configurations for all child nodes of the node selected by the given key allowing the caller
160     * to specify the {@code supportUpdates} flag.
161     *
162     * @param key the key for selecting the desired parent node
163     * @param supportUpdates a flag whether the returned sub configuration should be directly connected to its parent
164     * @return a collection with {@code HierarchicalConfiguration} objects for all child nodes of the selected parent node
165     */
166    List<HierarchicalConfiguration<T>> childConfigurationsAt(String key, boolean supportUpdates);
167
168    /**
169     * Removes all values of the property with the given name and of keys that start with this name. So if there is a
170     * property with the key &quot;foo&quot; and a property with the key &quot;foo.bar&quot;, a call of
171     * {@code clearTree("foo")} would remove both properties.
172     *
173     * @param key the key of the property to be removed
174     */
175    void clearTree(String key);
176}