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.List; 020 021import org.apache.commons.configuration2.tree.ExpressionEngine; 022 023/** 024 * <p> 025 * An interface for immutable hierarchical configurations. 026 * </p> 027 * <p> 028 * There are some sources of configuration data that cannot be stored very well 029 * in a flat configuration object (like {@link BaseConfiguration}) because then 030 * their structure is lost. A prominent example are XML documents. 031 * </p> 032 * <p> 033 * This interface extends the basic {@link ImmutableConfiguration} interface by 034 * structured access to configuration properties. An {@link ExpressionEngine} is 035 * used to evaluate complex property keys and to map them to nodes of a 036 * tree-like structure. 037 * </p> 038 * 039 * @since 2.0 040 */ 041public interface ImmutableHierarchicalConfiguration extends ImmutableConfiguration 042{ 043 /** 044 * Returns the expression engine used by this configuration. This method 045 * will never return <b>null</b>; if no specific expression engine was set, 046 * the default expression engine will be returned. 047 * 048 * @return the current expression engine 049 */ 050 ExpressionEngine getExpressionEngine(); 051 052 /** 053 * Returns the maximum defined index for the given key. This is useful if 054 * there are multiple values for this key. They can then be addressed 055 * separately by specifying indices from 0 to the return value of this 056 * method. 057 * 058 * @param key the key to be checked 059 * @return the maximum defined index for this key 060 */ 061 int getMaxIndex(String key); 062 063 /** 064 * Returns the name of the root element of this configuration. This 065 * information may be of use in some cases, e.g. for sub configurations 066 * created using the {@code immutableConfigurationsAt()} method. The exact 067 * meaning of the string returned by this method is specific to a concrete 068 * implementation. For instance, an XML configuration might return the name 069 * of the document element. 070 * 071 * @return the name of the root element of this configuration 072 */ 073 String getRootElementName(); 074 075 /** 076 * <p> 077 * Returns an immutable hierarchical 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 #immutableSubset(String)} method is that 088 * {@code immutableSubset()} supports arbitrary subsets of configuration nodes 089 * while {@code immutableConfigurationAt()} only returns a single sub tree. 090 * Please refer to the documentation of the 091 * {@code SubnodeConfiguration} class to obtain further information 092 * about subnode configurations and when they should be used. 093 * </p> 094 * 095 * @param key the key that selects the sub tree 096 * @param supportUpdates a flag whether the returned subnode configuration 097 * should be able to handle updates of its parent 098 * @return a hierarchical configuration that contains this sub tree 099 */ 100 ImmutableHierarchicalConfiguration immutableConfigurationAt(String key, 101 boolean supportUpdates); 102 103 /** 104 * Returns an immutable hierarchical configuration for the node specified by 105 * the given key. This is a short form for {@code immutableConfigurationAt(key, 106 * <b>false</b>)}. 107 * 108 * @param key the key that selects the sub tree 109 * @return a hierarchical configuration that contains this sub tree 110 */ 111 ImmutableHierarchicalConfiguration immutableConfigurationAt(String key); 112 113 /** 114 * Returns a list of immutable configurations for all configuration nodes selected 115 * by the given key. This method will evaluate the passed in key (using the 116 * current {@code ExpressionEngine}) and then create an immutable subnode 117 * configuration for each returned node (like 118 * {@link #immutableConfigurationAt(String)}}). This is especially 119 * useful when dealing with list-like structures. As an example consider the 120 * configuration that contains data about database tables and their fields. 121 * If you need access to all fields of a certain table, you can simply do 122 * 123 * <pre> 124 * List<ImmutableHierarchicalConfiguration> fields = 125 * config.immutableConfigurationsAt("tables.table(0).fields.field"); 126 * for(Iterator<ImmutableHierarchicalConfiguration> it = fields.iterator(); 127 * it.hasNext();) 128 * { 129 * ImmutableHierarchicalConfiguration sub = it.next(); 130 * // now the children and attributes of the field node can be 131 * // directly accessed 132 * String fieldName = sub.getString("name"); 133 * String fieldType = sub.getString("type"); 134 * ... 135 * </pre> 136 * 137 * @param key the key for selecting the desired nodes 138 * @return a list with immutable hierarchical configuration objects; each 139 * configuration represents one of the nodes selected by the passed in key 140 */ 141 List<ImmutableHierarchicalConfiguration> immutableConfigurationsAt(String key); 142 143 /** 144 * Returns a list of immutable configurations for all direct child elements 145 * of the node selected by the given key. With this method it is possible to 146 * inspect the content of a hierarchical structure; all children of a given 147 * node can be queried without having to know their exact names. If the 148 * passed in key does not point to a single node, an empty list is returned. 149 * This is also the result if the node referred to by the key does not have 150 * child elements. 151 * 152 * @param key the key for selecting the desired parent node 153 * @return a collection with immutable configurations for all child nodes of 154 * the selected parent node 155 */ 156 List<ImmutableHierarchicalConfiguration> immutableChildConfigurationsAt( 157 String key); 158}