    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
    031 * configuration sources. Also, all methods defined by the {@code Configuration}
    032 * interface are available.
    033 * </p>
    034 * <p>
    035 * This interface does not make any assumptions about the concrete type of nodes
    036 * used by an implementation; this is reflected by a generic type parameter.
    037 * Concrete implementations may therefore define their own hierarchical
    038 * structures.
    039 * </p>
    040 *
    041 * @since 2.0
    042 * @param <T> the type of the nodes used by this hierarchical configuration
    043 */
    044public interface HierarchicalConfiguration<T>
    045    extends Configuration, ImmutableHierarchicalConfiguration, NodeModelSupport<T>
    046{
    047    /**
    048     * Sets the expression engine to be used by this configuration. All property
    049     * keys this configuration has to deal with will be interpreted by this
    050     * engine.
    051     *
    052     * @param expressionEngine the new expression engine; can be <b>null</b>,
    053     * then the default expression engine will be used
    054     */
    055    void setExpressionEngine(ExpressionEngine expressionEngine);
    056
    057    /**
    058     * Adds a collection of nodes at the specified position of the configuration
    059     * tree. This method works similar to {@code addProperty()}, but
    060     * instead of a single property a whole collection of nodes can be added -
    061     * and thus complete configuration sub trees. E.g. with this method it is
    062     * possible to add parts of another {@code BaseHierarchicalConfiguration}
    063     * object to this object. If the passed in key refers to
    064     * an existing and unique node, the new nodes are added to this node.
    065     * Otherwise a new node will be created at the specified position in the
    066     * hierarchy.
    067     *
    068     * @param key the key where the nodes are to be added; can be <b>null </b>,
    069     * then they are added to the root node
    070     * @param nodes a collection with the {@code Node} objects to be
    071     * added
    072     */
    073    void addNodes(String key, Collection<? extends T> nodes);
    074
    075    /**
    076     * <p>
    077     * Returns a hierarchical sub configuration object that wraps the
    078     * configuration node specified by the given key. This method provides an
    079     * easy means of accessing sub trees of a hierarchical configuration. In the
    080     * returned configuration the sub tree can directly be accessed, it becomes
    081     * the root node of this configuration. Because of this the passed in key
    082     * must select exactly one configuration node; otherwise an
    083     * {@code IllegalArgumentException} will be thrown.
    084     * </p>
    085     * <p>
    086     * The difference between this method and the
    087     * {@link #subset(String)} method is that
    088     * {@code subset()} supports arbitrary subsets of configuration nodes
    089     * while {@code configurationAt()} only returns a single sub tree.
    090     * Please refer to the documentation of the
    091     * {@link SubnodeConfiguration} class to obtain further information
    092     * about sub configurations and when they should be used.
    093     * </p>
    094     * <p>
    095     * With the {@code supportUpdate} flag the behavior of the returned
    096     * sub configuration regarding updates of its parent
    097     * configuration can be determined. If set to <b>false</b>, the configurations
    098     * return on independent nodes structures. So changes made on one configuration
    099     * cannot be seen by the other one. A value of <b>true</b> in contrast creates
    100     * a direct connection between both configurations - they are then using the
    101     * same underlying data structures as much as possible. There are however changes
    102     * which break this connection; for instance, if the sub tree the sub configuration
    103     * belongs to is completely removed from the parent configuration. If such a
    104     * change happens, the sub configuration becomes detached from its parent.
    105     * It can still be used in a normal way, but changes on it are not reflected
    106     * by the parent and vice verse. Also, it is not possible to reattach a once
    107     * detached sub configuration.
    108     * </p>
    109     *
    110     * @param key the key that selects the sub tree
    111     * @param supportUpdates a flag whether the returned sub configuration
    112     * should be directly connected to its parent
    113     * @return a hierarchical configuration that contains this sub tree
    114     * @see SubnodeConfiguration
    115     */
    116    HierarchicalConfiguration<T> configurationAt(String key, boolean supportUpdates);
    117
    118    /**
    119     * Returns a hierarchical subnode configuration for the node specified by
    120     * the given key. This is a short form for {@code configurationAt(key,
    121     * <b>false</b>)}.
    122     *
    123     * @param key the key that selects the sub tree
    124     * @return a hierarchical configuration that contains this sub tree
    125     * @see SubnodeConfiguration
    126     */
    127    HierarchicalConfiguration<T> configurationAt(String key);
    128
    129    /**
    130     * Returns a list of sub configurations for all configuration nodes selected
    131     * by the given key. This method will evaluate the passed in key (using the
    132     * current {@code ExpressionEngine}) and then create a sub configuration for
    133     * each returned node (like {@link #configurationAt(String)} ). This is
    134     * especially useful when dealing with list-like structures. As an example
    135     * consider the configuration that contains data about database tables and
    136     * their fields. If you need access to all fields of a certain table, you
    137     * can simply do
    138     *
    139     * <pre>
    140     * List fields = config.configurationsAt("tables.table(0).fields.field");
    141     * for(Iterator it = fields.iterator(); it.hasNext();)
    142     * {
    143     *     BaseHierarchicalConfiguration sub = (BaseHierarchicalConfiguration) it.next();
    144     *     // now the children and attributes of the field node can be
    145     *     // directly accessed
    146     *     String fieldName = sub.getString("name");
    147     *     String fieldType = sub.getString("type");
    148     *     ...
    149     * </pre>
    150     *
    151     * The configuration objects returned are <strong>not</strong> connected to
    152     * the parent configuration.
    153     *
    154     * @param key the key for selecting the desired nodes
    155     * @return a list with hierarchical configuration objects; each
    156     *         configuration represents one of the nodes selected by the passed
    157     *         in key
    158     */
    159    List<HierarchicalConfiguration<T>> configurationsAt(String key);
    160
    161    /**
    162     * Returns a list of sub configurations for all configuration nodes selected
    163     * by the given key allowing the caller to specify the
    164     * {@code supportUpdates} flag. This method works like
    165     * {@link #configurationsAt(String)}, but with the additional boolean
    166     * parameter it can be specified whether the returned configurations react
    167     * on updates of the parent configuration.
    168     *
    169     * @param key the key for selecting the desired nodes
    170     * @param supportUpdates a flag whether the returned sub configuration
    171     *        should be directly connected to its parent
    172     * @return a list with hierarchical configuration objects; each
    173     *         configuration represents one of the nodes selected by the passed
    174     *         in key
    175     * @see #configurationsAt(String, boolean)
    176     */
    177    List<HierarchicalConfiguration<T>> configurationsAt(String key,
    178            boolean supportUpdates);
    179
    180    /**
    181     * Returns a list with sub configurations for all child nodes of the node
    182     * selected by the given key. This method works like
    183     * {@link #immutableChildConfigurationsAt(String)}, but returns a list with
    184     * mutable configuration objects. The configuration objects returned are
    185     * <strong>not</strong> connected to the parent configuration.
    186     *
    187     * @param key the key for selecting the desired parent node
    188     * @return a collection with {@code HierarchicalConfiguration} objects for all
    189     *         child nodes of the selected parent node
    190     */
    191    List<HierarchicalConfiguration<T>> childConfigurationsAt(String key);
    192
    193    /**
    194     * Returns a list with sub configurations for all child nodes of the node
    195     * selected by the given key allowing the caller to specify the
    196     * {@code supportUpdates} flag.
    197     *
    198     * @param key the key for selecting the desired parent node
    199     * @param supportUpdates a flag whether the returned sub configuration
    200     *        should be directly connected to its parent
    201     * @return a collection with {@code HierarchicalConfiguration} objects for
    202     *         all child nodes of the selected parent node
    203     */
    204    List<HierarchicalConfiguration<T>> childConfigurationsAt(String key,
    205            boolean supportUpdates);
    206
    207    /**
    208     * Removes all values of the property with the given name and of keys that
    209     * start with this name. So if there is a property with the key
    210     * &quot;foo&quot; and a property with the key &quot;foo.bar&quot;, a call
    211     * of {@code clearTree("foo")} would remove both properties.
    212     *
    213     * @param key the key of the property to be removed
    214     */
    215    void clearTree(String key);
    216}