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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.configuration2;
import java.util.List;
import org.apache.commons.configuration2.tree.ExpressionEngine;
/**
*
* An interface for immutable hierarchical configurations.
*
*
* There are some sources of configuration data that cannot be stored very well in a flat configuration object (like
* {@link BaseConfiguration}) because then their structure is lost. A prominent example are XML documents.
*
*
* This interface extends the basic {@link ImmutableConfiguration} interface by structured access to configuration
* properties. An {@link ExpressionEngine} is used to evaluate complex property keys and to map them to nodes of a
* tree-like structure.
*
*
* @since 2.0
*/
public interface ImmutableHierarchicalConfiguration extends ImmutableConfiguration {
/**
* Gets the expression engine used by this configuration. This method will never return null; if no specific
* expression engine was set, the default expression engine will be returned.
*
* @return the current expression engine
*/
ExpressionEngine getExpressionEngine();
/**
* Gets the maximum defined index for the given key. This is useful if there are multiple values for this key. They
* can then be addressed separately by specifying indices from 0 to the return value of this method.
*
* @param key the key to be checked
* @return the maximum defined index for this key
*/
int getMaxIndex(String key);
/**
* Gets the name of the root element of this configuration. This information may be of use in some cases, e.g. for
* sub configurations created using the {@code immutableConfigurationsAt()} method. The exact meaning of the string
* returned by this method is specific to a concrete implementation. For instance, an XML configuration might return the
* name of the document element.
*
* @return the name of the root element of this configuration
*/
String getRootElementName();
/**
* Returns a list of immutable configurations for all direct child elements of the node selected by the given key. With
* this method it is possible to inspect the content of a hierarchical structure; all children of a given node can be
* queried without having to know their exact names. If the passed in key does not point to a single node, an empty list
* is returned. This is also the result if the node referred to by the key does not have child elements.
*
* @param key the key for selecting the desired parent node
* @return a collection with immutable configurations for all child nodes of the selected parent node
*/
List immutableChildConfigurationsAt(String key);
/**
* Returns an immutable hierarchical configuration for the node specified by the given key. This is a short form for
* {@code immutableConfigurationAt(key,
* false)}.
*
* @param key the key that selects the sub tree
* @return a hierarchical configuration that contains this sub tree
*/
ImmutableHierarchicalConfiguration immutableConfigurationAt(String key);
/**
*
* Returns an immutable hierarchical configuration object that wraps the configuration node specified by the given key.
* This method provides an easy means of accessing sub trees of a hierarchical configuration. In the returned
* configuration the sub tree can directly be accessed, it becomes the root node of this configuration. Because of this
* the passed in key must select exactly one configuration node; otherwise an {@code IllegalArgumentException} will be
* thrown.
*
*
* The difference between this method and the {@link #immutableSubset(String)} method is that {@code immutableSubset()}
* supports arbitrary subsets of configuration nodes while {@code immutableConfigurationAt()} only returns a single sub
* tree. Please refer to the documentation of the {@code SubnodeConfiguration} class to obtain further information about
* subnode configurations and when they should be used.
*
*
* @param key the key that selects the sub tree
* @param supportUpdates a flag whether the returned subnode configuration should be able to handle updates of its
* parent
* @return a hierarchical configuration that contains this sub tree
*/
ImmutableHierarchicalConfiguration immutableConfigurationAt(String key, boolean supportUpdates);
/**
* Returns a list of immutable configurations for all configuration nodes selected by the given key. This method will
* evaluate the passed in key (using the current {@code ExpressionEngine}) and then create an immutable subnode
* configuration for each returned node (like {@link #immutableConfigurationAt(String)}}). This is especially useful
* when dealing with list-like structures. As an example consider the configuration that contains data about database
* tables and their fields. If you need access to all fields of a certain table, you can simply do
*
*
* List<ImmutableHierarchicalConfiguration> fields =
* config.immutableConfigurationsAt("tables.table(0).fields.field");
* for(Iterator<ImmutableHierarchicalConfiguration> it = fields.iterator();
* it.hasNext();)
* {
* ImmutableHierarchicalConfiguration sub = it.next();
* // now the children and attributes of the field node can be
* // directly accessed
* String fieldName = sub.getString("name");
* String fieldType = sub.getString("type");
* ...
*
*
* @param key the key for selecting the desired nodes
* @return a list with immutable hierarchical configuration objects; each configuration represents one of the nodes
* selected by the passed in key
*/
List immutableConfigurationsAt(String key);
}