    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.builder.combined;
    018
    019import java.net.URL;
    020import java.util.ArrayList;
    021import java.util.Collection;
    022import java.util.Collections;
    023import java.util.HashMap;
    024import java.util.Iterator;
    025import java.util.LinkedList;
    026import java.util.List;
    027import java.util.Map;
    028import java.util.Set;
    029import java.util.stream.Collectors;
    030
    031import org.apache.commons.configuration2.CombinedConfiguration;
    032import org.apache.commons.configuration2.Configuration;
    033import org.apache.commons.configuration2.ConfigurationLookup;
    034import org.apache.commons.configuration2.HierarchicalConfiguration;
    035import org.apache.commons.configuration2.SystemConfiguration;
    036import org.apache.commons.configuration2.XMLConfiguration;
    037import org.apache.commons.configuration2.beanutils.BeanDeclaration;
    038import org.apache.commons.configuration2.beanutils.BeanHelper;
    039import org.apache.commons.configuration2.beanutils.CombinedBeanDeclaration;
    040import org.apache.commons.configuration2.beanutils.XMLBeanDeclaration;
    041import org.apache.commons.configuration2.builder.BasicBuilderParameters;
    042import org.apache.commons.configuration2.builder.BasicConfigurationBuilder;
    043import org.apache.commons.configuration2.builder.BuilderParameters;
    044import org.apache.commons.configuration2.builder.ConfigurationBuilder;
    045import org.apache.commons.configuration2.builder.ConfigurationBuilderEvent;
    046import org.apache.commons.configuration2.builder.FileBasedBuilderParametersImpl;
    047import org.apache.commons.configuration2.builder.FileBasedBuilderProperties;
    048import org.apache.commons.configuration2.builder.FileBasedConfigurationBuilder;
    049import org.apache.commons.configuration2.builder.XMLBuilderParametersImpl;
    050import org.apache.commons.configuration2.builder.XMLBuilderProperties;
    051import org.apache.commons.configuration2.event.EventListener;
    052import org.apache.commons.configuration2.ex.ConfigurationException;
    053import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
    054import org.apache.commons.configuration2.interpol.Lookup;
    055import org.apache.commons.configuration2.io.FileSystem;
    056import org.apache.commons.configuration2.resolver.CatalogResolver;
    057import org.apache.commons.configuration2.tree.DefaultExpressionEngineSymbols;
    058import org.apache.commons.configuration2.tree.OverrideCombiner;
    059import org.apache.commons.configuration2.tree.UnionCombiner;
    060import org.xml.sax.EntityResolver;
    061
    062/**
    063 * <p>
    064 * A specialized {@code ConfigurationBuilder} implementation that creates a {@link CombinedConfiguration} from multiple
    065 * configuration sources defined by an XML-based <em>configuration definition file</em>.
    066 * </p>
    067 * <p>
    068 * This class provides an easy and flexible means for loading multiple configuration sources and combining the results
    069 * into a single configuration object. The sources to be loaded are defined in an XML document that can contain certain
    070 * tags representing the different supported configuration classes. If such a tag is found, a corresponding
    071 * {@code ConfigurationBuilder} class is instantiated and initialized using the classes of the {@code beanutils} package
    072 * (namely {@link org.apache.commons.configuration2.beanutils.XMLBeanDeclaration XMLBeanDeclaration} will be used to
    073 * extract the configuration's initialization parameters, which allows for complex initialization scenarios).
    074 * </p>
    075 * <p>
    076 * It is also possible to add custom tags to the configuration definition file. For this purpose an implementation of
    077 * {@link CombinedConfigurationBuilderProvider} has to be created which is responsible for the creation of a
    078 * {@code ConfigurationBuilder} associated with the custom tag. An instance of this class has to be registered at the
    079 * {@link CombinedBuilderParametersImpl} object which is used to initialize this {@code CombinedConfigurationBuilder}.
    080 * This provider will then be called when the corresponding custom tag is detected. For many default configuration
    081 * classes providers are already registered.
    082 * </p>
    083 * <p>
    084 * The configuration definition file has the following basic structure:
    085 * </p>
    086 *
    087 * <pre>
    088 * &lt;configuration systemProperties="properties file name"&gt;
    089 *   &lt;header&gt;
    090 *     &lt;!-- Optional meta information about the combined configuration --&gt;
    091 *   &lt;/header&gt;
    092 *   &lt;override&gt;
    093 *     &lt;!-- Declarations for override configurations --&gt;
    094 *   &lt;/override&gt;
    095 *   &lt;additional&gt;
    096 *     &lt;!-- Declarations for union configurations --&gt;
    097 *   &lt;/additional&gt;
    098 * &lt;/configuration&gt;
    099 * </pre>
    100 *
    101 * <p>
    102 * The name of the root element (here {@code configuration}) is arbitrary. The optional {@code systemProperties}
    103 * attribute identifies the path to a property file containing properties that should be added to the system properties.
    104 * If specified on the root element, the system properties are set before the rest of the configuration is processed.
    105 * </p>
    106 * <p>
    107 * There are two sections (both of them are optional) for declaring <em>override</em> and <em>additional</em>
    108 * configurations. Configurations in the former section are evaluated in the order of their declaration, and properties
    109 * of configurations declared earlier hide those of configurations declared later. Configurations in the latter section
    110 * are combined to a union configuration, i.e. all of their properties are added to a large hierarchical configuration.
    111 * Configuration declarations that occur as direct children of the root element are treated as override declarations.
    112 * </p>
    113 * <p>
    114 * Each configuration declaration consists of a tag whose name is associated with a
    115 * {@code CombinedConfigurationBuilderProvider}. This can be one of the predefined tags like {@code properties}, or
    116 * {@code xml}, or a custom tag, for which a configuration builder provider was registered (as described above).
    117 * Attributes and sub elements with specific initialization parameters can be added. There are some reserved attributes
    118 * with a special meaning that can be used in every configuration declaration:
    119 * </p>
    120 * <table border="1">
    121 * <caption>Standard attributes for configuration declarations</caption>
    122 * <tr>
    123 * <th>Attribute</th>
    124 * <th>Meaning</th>
    125 * </tr>
    126 * <tr>
    127 * <td>{@code config-name}</td>
    128 * <td>Allows specifying a name for this configuration. This name can be used to obtain a reference to the configuration
    129 * from the resulting combined configuration (see below). It can also be passed to the {@link #getNamedBuilder(String)}
    130 * method.</td>
    131 * </tr>
    132 * <tr>
    133 * <td>{@code config-at}</td>
    134 * <td>With this attribute an optional prefix can be specified for the properties of the corresponding
    135 * configuration.</td>
    136 * </tr>
    137 * <tr>
    138 * <td>{@code config-optional}</td>
    139 * <td>Declares a configuration source as optional. This means that errors that occur when creating the configuration
    140 * are ignored.</td>
    141 * </tr>
    142 * <tr>
    143 * <td>{@code config-reload}</td>
    144 * <td>Many configuration sources support a reloading mechanism. For those sources it is possible to enable reloading by
    145 * providing this attribute with a value of <strong>true</strong>.</td>
    146 * </tr>
    147 * </table>
    148 * <p>
    149 * The optional <em>header</em> section can contain some meta data about the created configuration itself. For instance,
    150 * it is possible to set further properties of the {@code NodeCombiner} objects used for constructing the resulting
    151 * configuration.
    152 * </p>
    153 * <p>
    154 * The default configuration object returned by this builder is an instance of the {@link CombinedConfiguration} class.
    155 * This allows for convenient access to the configuration objects maintained by the combined configuration (e.g. for
    156 * updates of single configuration objects). It has also the advantage that the properties stored in all declared
    157 * configuration objects are collected and transformed into a single hierarchical structure, which can be accessed using
    158 * different expression engines. The actual {@code CombinedConfiguration} implementation can be overridden by specifying
    159 * the class in the <em>config-class</em> attribute of the result element.
    160 * </p>
    161 * <p>
    162 * A custom EntityResolver can be used for all XMLConfigurations by adding
    163 * </p>
    164 *
    165 * <pre>
    166 * &lt;entity-resolver config-class="EntityResolver fully qualified class name"&gt;
    167 * </pre>
    168 *
    169 * <p>
    170 * A specific CatalogResolver can be specified for all XMLConfiguration sources by adding
    171 * </p>
    172 *
    173 * <pre>
    174 * &lt;entity-resolver catalogFiles="comma separated list of catalog files"&gt;
    175 * </pre>
    176 *
    177 * <p>
    178 * Additional ConfigurationProviders can be added by configuring them in the <em>header</em> section.
    179 * </p>
    180 *
    181 * <pre>
    182 * &lt;providers&gt;
    183 *   &lt;provider config-tag="tag name" config-class="provider fully qualified class name"/&gt;
    184 * &lt;/providers&gt;
    185 * </pre>
    186 *
    187 * <p>
    188 * Additional variable resolvers can be added by configuring them in the <em>header</em> section.
    189 * </p>
    190 *
    191 * <pre>
    192 * &lt;lookups&gt;
    193 *   &lt;lookup config-prefix="prefix" config-class="StrLookup fully qualified class name"/&gt;
    194 * &lt;/lookups&gt;
    195 * </pre>
    196 *
    197 * <p>
    198 * All declared override configurations are directly added to the resulting combined configuration. If they are given
    199 * names (using the {@code config-name} attribute), they can directly be accessed using the
    200 * {@code getConfiguration(String)} method of {@code CombinedConfiguration}. The additional configurations are
    201 * altogether added to another combined configuration, which uses a union combiner. Then this union configuration is
    202 * added to the resulting combined configuration under the name defined by the {@code ADDITIONAL_NAME} constant. The
    203 * {@link #getNamedBuilder(String)} method can be used to access the {@code ConfigurationBuilder} objects for all
    204 * configuration sources which have been assigned a name; care has to be taken that these names are unique.
    205 * </p>
    206 *
    207 * @since 1.3
    208 */
    209public class CombinedConfigurationBuilder extends BasicConfigurationBuilder<CombinedConfiguration> {
    210    /**
    211     * Constant for the name of the additional configuration. If the configuration definition file contains an
    212     * {@code additional} section, a special union configuration is created and added under this name to the resulting
    213     * combined configuration.
    214     */
    215    public static final String ADDITIONAL_NAME = CombinedConfigurationBuilder.class.getName() + "/ADDITIONAL_CONFIG";
    216
    217    /** Constant for the name of the configuration bean factory. */
    218    static final String CONFIG_BEAN_FACTORY_NAME = CombinedConfigurationBuilder.class.getName() + ".CONFIG_BEAN_FACTORY_NAME";
    219
    220    /** Constant for the reserved name attribute. */
    221    static final String ATTR_NAME = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START + XMLBeanDeclaration.RESERVED_PREFIX + "name"
    222        + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
    223
    224    /** Constant for the name of the at attribute. */
    225    static final String ATTR_ATNAME = "at";
    226
    227    /** Constant for the reserved at attribute. */
    228    static final String ATTR_AT_RES = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START + XMLBeanDeclaration.RESERVED_PREFIX + ATTR_ATNAME
    229        + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
    230
    231    /** Constant for the at attribute without the reserved prefix. */
    232    static final String ATTR_AT = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START + ATTR_ATNAME + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
    233
    234    /** Constant for the name of the optional attribute. */
    235    static final String ATTR_OPTIONALNAME = "optional";
    236
    237    /** Constant for the reserved optional attribute. */
    238    static final String ATTR_OPTIONAL_RES = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START + XMLBeanDeclaration.RESERVED_PREFIX + ATTR_OPTIONALNAME
    239        + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
    240
    241    /** Constant for the optional attribute without the reserved prefix. */
    242    static final String ATTR_OPTIONAL = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START + ATTR_OPTIONALNAME
    243        + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
    244
    245    /** Constant for the forceCreate attribute. */
    246    static final String ATTR_FORCECREATE = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START + XMLBeanDeclaration.RESERVED_PREFIX + "forceCreate"
    247        + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
    248
    249    /** Constant for the reload attribute. */
    250    static final String ATTR_RELOAD = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START + XMLBeanDeclaration.RESERVED_PREFIX + "reload"
    251        + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
    252
    253    /**
    254     * Constant for the tag attribute for providers.
    255     */
    256    static final String KEY_SYSTEM_PROPS = "[@systemProperties]";
    257
    258    /** Constant for the name of the header section. */
    259    static final String SEC_HEADER = "header";
    260
    261    /** Constant for an expression that selects the union configurations. */
    262    static final String KEY_UNION = "additional";
    263
    264    /** An array with the names of top level configuration sections. */
    265    static final String[] CONFIG_SECTIONS = {"additional", "override", SEC_HEADER};
    266
    267    /**
    268     * Constant for an expression that selects override configurations in the override section.
    269     */
    270    static final String KEY_OVERRIDE = "override";
    271
    272    /**
    273     * Constant for the key that points to the list nodes definition of the override combiner.
    274     */
    275    static final String KEY_OVERRIDE_LIST = SEC_HEADER + ".combiner.override.list-nodes.node";
    276
    277    /**
    278     * Constant for the key that points to the list nodes definition of the additional combiner.
    279     */
    280    static final String KEY_ADDITIONAL_LIST = SEC_HEADER + ".combiner.additional.list-nodes.node";
    281
    282    /**
    283     * Constant for the key for defining providers in the configuration file.
    284     */
    285    static final String KEY_CONFIGURATION_PROVIDERS = SEC_HEADER + ".providers.provider";
    286
    287    /**
    288     * Constant for the tag attribute for providers.
    289     */
    290    static final String KEY_PROVIDER_KEY = XMLBeanDeclaration.ATTR_PREFIX + "tag]";
    291
    292    /**
    293     * Constant for the key for defining variable resolvers
    294     */
    295    static final String KEY_CONFIGURATION_LOOKUPS = SEC_HEADER + ".lookups.lookup";
    296
    297    /**
    298     * Constant for the key for defining entity resolvers
    299     */
    300    static final String KEY_ENTITY_RESOLVER = SEC_HEADER + ".entity-resolver";
    301
    302    /**
    303     * Constant for the prefix attribute for lookups.
    304     */
    305    static final String KEY_LOOKUP_KEY = XMLBeanDeclaration.ATTR_PREFIX + "prefix]";
    306
    307    /**
    308     * Constant for the FileSystem.
    309     */
    310    static final String FILE_SYSTEM = SEC_HEADER + ".fileSystem";
    311
    312    /**
    313     * Constant for the key of the result declaration. This key can point to a bean declaration, which defines properties of
    314     * the resulting combined configuration.
    315     */
    316    static final String KEY_RESULT = SEC_HEADER + ".result";
    317
    318    /** Constant for the key of the combiner in the result declaration. */
    319    static final String KEY_COMBINER = KEY_RESULT + ".nodeCombiner";
    320
    321    /** Constant for the XML file extension. */
    322    static final String EXT_XML = "xml";
    323
    324    /** Constant for the basic configuration builder class. */
    325    private static final String BASIC_BUILDER = "org.apache.commons.configuration2.builder.BasicConfigurationBuilder";
    326
    327    /** Constant for the file-based configuration builder class. */
    328    private static final String FILE_BUILDER = "org.apache.commons.configuration2.builder.FileBasedConfigurationBuilder";
    329
    330    /** Constant for the reloading file-based configuration builder class. */
    331    private static final String RELOADING_BUILDER = "org.apache.commons.configuration2.builder.ReloadingFileBasedConfigurationBuilder";
    332
    333    /** Constant for the name of the file-based builder parameters class. */
    334    private static final String FILE_PARAMS = "org.apache.commons.configuration2.builder.FileBasedBuilderParametersImpl";
    335
    336    /** Constant for the provider for properties files. */
    337    private static final ConfigurationBuilderProvider PROPERTIES_PROVIDER = new FileExtensionConfigurationBuilderProvider(FILE_BUILDER, RELOADING_BUILDER,
    338        "org.apache.commons.configuration2.XMLPropertiesConfiguration", "org.apache.commons.configuration2.PropertiesConfiguration", EXT_XML,
    339        Collections.singletonList(FILE_PARAMS));
    340
    341    /** Constant for the provider for XML files. */
    342    private static final ConfigurationBuilderProvider XML_PROVIDER = new BaseConfigurationBuilderProvider(FILE_BUILDER, RELOADING_BUILDER,
    343        "org.apache.commons.configuration2.XMLConfiguration", Collections.singletonList("org.apache.commons.configuration2.builder.XMLBuilderParametersImpl"));
    344
    345    /** Constant for the provider for JNDI sources. */
    346    private static final BaseConfigurationBuilderProvider JNDI_PROVIDER = new BaseConfigurationBuilderProvider(BASIC_BUILDER, null,
    347        "org.apache.commons.configuration2.JNDIConfiguration",
    348        Collections.singletonList("org.apache.commons.configuration2.builder.JndiBuilderParametersImpl"));
    349
    350    /** Constant for the provider for system properties. */
    351    private static final BaseConfigurationBuilderProvider SYSTEM_PROVIDER = new BaseConfigurationBuilderProvider(BASIC_BUILDER, null,
    352        "org.apache.commons.configuration2.SystemConfiguration", Collections.singletonList("org.apache.commons.configuration2.builder.BasicBuilderParameters"));
    353
    354    /** Constant for the provider for ini files. */
    355    private static final BaseConfigurationBuilderProvider INI_PROVIDER = new BaseConfigurationBuilderProvider(FILE_BUILDER, RELOADING_BUILDER,
    356        "org.apache.commons.configuration2.INIConfiguration", Collections.singletonList(FILE_PARAMS));
    357
    358    /** Constant for the provider for environment properties. */
    359    private static final BaseConfigurationBuilderProvider ENV_PROVIDER = new BaseConfigurationBuilderProvider(BASIC_BUILDER, null,
    360        "org.apache.commons.configuration2.EnvironmentConfiguration",
    361        Collections.singletonList("org.apache.commons.configuration2.builder.BasicBuilderParameters"));
    362
    363    /** Constant for the provider for plist files. */
    364    private static final BaseConfigurationBuilderProvider PLIST_PROVIDER = new FileExtensionConfigurationBuilderProvider(FILE_BUILDER, RELOADING_BUILDER,
    365        "org.apache.commons.configuration2.plist.XMLPropertyListConfiguration", "org.apache.commons.configuration2.plist.PropertyListConfiguration", EXT_XML,
    366        Collections.singletonList(FILE_PARAMS));
    367
    368    /** Constant for the provider for configuration definition files. */
    369    private static final BaseConfigurationBuilderProvider COMBINED_PROVIDER = new CombinedConfigurationBuilderProvider();
    370
    371    /** Constant for the provider for multiple XML configurations. */
    372    private static final MultiFileConfigurationBuilderProvider MULTI_XML_PROVIDER = new MultiFileConfigurationBuilderProvider(
    373        "org.apache.commons.configuration2.XMLConfiguration", "org.apache.commons.configuration2.builder.XMLBuilderParametersImpl");
    374
    375    /** An array with the names of the default tags. */
    376    private static final String[] DEFAULT_TAGS = {"properties", "xml", "hierarchicalXml", "plist", "ini", "system", "env", "jndi", "configuration",
    377        "multiFile"};
    378
    379    /** An array with the providers for the default tags. */
    380    private static final ConfigurationBuilderProvider[] DEFAULT_PROVIDERS = {PROPERTIES_PROVIDER, XML_PROVIDER, XML_PROVIDER, PLIST_PROVIDER, INI_PROVIDER,
    381        SYSTEM_PROVIDER, ENV_PROVIDER, JNDI_PROVIDER, COMBINED_PROVIDER, MULTI_XML_PROVIDER};
    382
    383    /** A map with the default configuration builder providers. */
    384    private static final Map<String, ConfigurationBuilderProvider> DEFAULT_PROVIDERS_MAP;
    385
    386    /** The builder for the definition configuration. */
    387    private ConfigurationBuilder<? extends HierarchicalConfiguration<?>> definitionBuilder;
    388
    389    /** Stores temporarily the configuration with the builder definitions. */
    390    private HierarchicalConfiguration<?> definitionConfiguration;
    391
    392    /** The object with data about configuration sources. */
    393    private ConfigurationSourceData sourceData;
    394
    395    /** Stores the current parameters object. */
    396    private CombinedBuilderParametersImpl currentParameters;
    397
    398    /** The current XML parameters object. */
    399    private XMLBuilderParametersImpl currentXMLParameters;
    400
    401    /** The configuration that is currently constructed. */
    402    private CombinedConfiguration currentConfiguration;
    403
    404    /**
    405     * A {@code ConfigurationInterpolator} to be used as parent for all child configurations to enable cross-source
    406     * interpolation.
    407     */
    408    private ConfigurationInterpolator parentInterpolator;
    409
    410    /**
    411     * Creates a new instance of {@code CombinedConfigurationBuilder}. No parameters are set.
    412     */
    413    public CombinedConfigurationBuilder() {
    414        super(CombinedConfiguration.class);
    415    }
    416
    417    /**
    418     *
    419     * Creates a new instance of {@code CombinedConfigurationBuilder} and sets the specified initialization parameters.
    420     *
    421     * @param params a map with initialization parameters
    422     */
    423    public CombinedConfigurationBuilder(final Map<String, Object> params) {
    424        super(CombinedConfiguration.class, params);
    425    }
    426
    427    /**
    428     *
    429     * Creates a new instance of {@code CombinedConfigurationBuilder} and sets the specified initialization parameters and
    430     * the <em>allowFailOnInit</em> flag.
    431     *
    432     * @param params a map with initialization parameters
    433     * @param allowFailOnInit the <em>allowFailOnInit</em> flag
    434     */
    435    public CombinedConfigurationBuilder(final Map<String, Object> params, final boolean allowFailOnInit) {
    436        super(CombinedConfiguration.class, params, allowFailOnInit);
    437    }
    438
    439    /**
    440     * Gets the {@code ConfigurationBuilder} which creates the definition configuration.
    441     *
    442     * @return the builder for the definition configuration
    443     * @throws ConfigurationException if an error occurs
    444     */
    445    public synchronized ConfigurationBuilder<? extends HierarchicalConfiguration<?>> getDefinitionBuilder() throws ConfigurationException {
    446        if (definitionBuilder == null) {
    447            definitionBuilder = setupDefinitionBuilder(getParameters());
    448            addDefinitionBuilderChangeListener(definitionBuilder);
    449        }
    450        return definitionBuilder;
    451    }
    452
    453    /**
    454     * {@inheritDoc} This method is overridden to adapt the return type.
    455     */
    456    @Override
    457    public CombinedConfigurationBuilder configure(final BuilderParameters... params) {
    458        super.configure(params);
    459        return this;
    460    }
    461
    462    /**
    463     * <p>
    464     * Gets the configuration builder with the given name. With this method a builder of a child configuration which was
    465     * given a name in the configuration definition file can be accessed directly.
    466     * </p>
    467     * <p>
    468     * <strong>Important note:</strong> This method only returns a meaningful result after the result configuration has been
    469     * created by calling {@code getConfiguration()}. If called before, always an exception is thrown.
    470     * </p>
    471     *
    472     * @param name the name of the builder in question
    473     * @return the child configuration builder with this name
    474     * @throws ConfigurationException if information about named builders is not yet available or no builder with this name
    475     *         exists
    476     */
    477    public synchronized ConfigurationBuilder<? extends Configuration> getNamedBuilder(final String name) throws ConfigurationException {
    478        if (sourceData == null) {
    479            throw new ConfigurationException("Information about child builders" + " has not been setup yet! Call getConfiguration() first.");
    480        }
    481        final ConfigurationBuilder<? extends Configuration> builder = sourceData.getNamedBuilder(name);
    482        if (builder == null) {
    483            throw new ConfigurationException("Builder cannot be resolved: " + name);
    484        }
    485        return builder;
    486    }
    487
    488    /**
    489     * <p>
    490     * Returns a set with the names of all child configuration builders. A tag defining a configuration source in the
    491     * configuration definition file can have the {@code config-name} attribute. If this attribute is present, the
    492     * corresponding builder is assigned this name and can be directly accessed through the {@link #getNamedBuilder(String)}
    493     * method. This method returns a collection with all available builder names.
    494     * </p>
    495     * <p>
    496     * <strong>Important note:</strong> This method only returns a meaningful result after the result configuration has been
    497     * created by calling {@code getConfiguration()}. If called before, always an empty set is returned.
    498     * </p>
    499     *
    500     * @return a set with the names of all builders
    501     */
    502    public synchronized Set<String> builderNames() {
    503        if (sourceData == null) {
    504            return Collections.emptySet();
    505        }
    506        return Collections.unmodifiableSet(sourceData.builderNames());
    507    }
    508
    509    /**
    510     * {@inheritDoc} This implementation resets some specific internal state of this builder.
    511     */
    512    @Override
    513    public synchronized void resetParameters() {
    514        super.resetParameters();
    515        definitionBuilder = null;
    516        definitionConfiguration = null;
    517        currentParameters = null;
    518        currentXMLParameters = null;
    519
    520        if (sourceData != null) {
    521            sourceData.cleanUp();
    522            sourceData = null;
    523        }
    524    }
    525
    526    /**
    527     * Obtains the {@code ConfigurationBuilder} object which provides access to the configuration containing the definition
    528     * of the combined configuration to create. If a definition builder is defined in the parameters, it is used. Otherwise,
    529     * we check whether the combined builder parameters object contains a parameters object for the definition builder. If
    530     * this is the case, a builder for an {@code XMLConfiguration} is created and configured with this object. As a last
    531     * resort, it is looked for a {@link FileBasedBuilderParametersImpl} object in the properties. If found, also a XML
    532     * configuration builder is created which loads this file. Note: This method is called from a synchronized block.
    533     *
    534     * @param params the current parameters for this builder
    535     * @return the builder for the definition configuration
    536     * @throws ConfigurationException if an error occurs
    537     */
    538    protected ConfigurationBuilder<? extends HierarchicalConfiguration<?>> setupDefinitionBuilder(final Map<String, Object> params)
    539        throws ConfigurationException {
    540        final CombinedBuilderParametersImpl cbParams = CombinedBuilderParametersImpl.fromParameters(params);
    541        if (cbParams != null) {
    542            final ConfigurationBuilder<? extends HierarchicalConfiguration<?>> defBuilder = cbParams.getDefinitionBuilder();
    543            if (defBuilder != null) {
    544                return defBuilder;
    545            }
    546
    547            if (cbParams.getDefinitionBuilderParameters() != null) {
    548                return createXMLDefinitionBuilder(cbParams.getDefinitionBuilderParameters());
    549            }
    550        }
    551
    552        final BuilderParameters fileParams = FileBasedBuilderParametersImpl.fromParameters(params);
    553        if (fileParams != null) {
    554            return createXMLDefinitionBuilder(fileParams);
    555        }
    556
    557        throw new ConfigurationException("No builder for configuration definition specified!");
    558    }
    559
    560    /**
    561     * Creates a default builder for the definition configuration and initializes it with a parameters object. This method
    562     * is called if no definition builder is defined in this builder's parameters. This implementation creates a default
    563     * file-based builder which produces an {@code XMLConfiguration}; it expects a corresponding file specification. Note:
    564     * This method is called in a synchronized block.
    565     *
    566     * @param builderParams the parameters object for the builder
    567     * @return the standard builder for the definition configuration
    568     */
    569    protected ConfigurationBuilder<? extends HierarchicalConfiguration<?>> createXMLDefinitionBuilder(final BuilderParameters builderParams) {
    570        return new FileBasedConfigurationBuilder<>(XMLConfiguration.class).configure(builderParams);
    571    }
    572
    573    /**
    574     * Gets the configuration containing the definition of the combined configuration to be created. This method only
    575     * returns a defined result during construction of the result configuration. The definition configuration is obtained
    576     * from the definition builder at first access and then stored temporarily to ensure that during result construction
    577     * always the same configuration instance is used. (Otherwise, it would be possible that the definition builder returns
    578     * a different instance when queried multiple times.)
    579     *
    580     * @return the definition configuration
    581     * @throws ConfigurationException if an error occurs
    582     */
    583    protected HierarchicalConfiguration<?> getDefinitionConfiguration() throws ConfigurationException {
    584        if (definitionConfiguration == null) {
    585            definitionConfiguration = getDefinitionBuilder().getConfiguration();
    586        }
    587        return definitionConfiguration;
    588    }
    589
    590    /**
    591     * Gets a collection with the builders for all child configuration sources. This method can be used by derived
    592     * classes providing additional functionality on top of the declared configuration sources. It only returns a defined
    593     * value during construction of the result configuration instance.
    594     *
    595     * @return a collection with the builders for child configuration sources
    596     */
    597    protected synchronized Collection<ConfigurationBuilder<? extends Configuration>> getChildBuilders() {
    598        return sourceData.getChildBuilders();
    599    }
    600
    601    /**
    602     * {@inheritDoc} This implementation evaluates the {@code result} property of the definition configuration. It creates a
    603     * combined bean declaration with both the properties specified in the definition file and the properties defined as
    604     * initialization parameters.
    605     */
    606    @Override
    607    protected BeanDeclaration createResultDeclaration(final Map<String, Object> params) throws ConfigurationException {
    608        final BeanDeclaration paramsDecl = super.createResultDeclaration(params);
    609        final XMLBeanDeclaration resultDecl = new XMLBeanDeclaration(getDefinitionConfiguration(), KEY_RESULT, true, CombinedConfiguration.class.getName());
    610        return new CombinedBeanDeclaration(resultDecl, paramsDecl);
    611    }
    612
    613    /**
    614     * {@inheritDoc} This implementation processes the definition configuration in order to
    615     * <ul>
    616     * <li>initialize the resulting {@code CombinedConfiguration}</li>
    617     * <li>determine the builders for all configuration sources</li>
    618     * <li>populate the resulting {@code CombinedConfiguration}</li>
    619     * </ul>
    620     */
    621    @Override
    622    protected void initResultInstance(final CombinedConfiguration result) throws ConfigurationException {
    623        super.initResultInstance(result);
    624
    625        currentConfiguration = result;
    626        final HierarchicalConfiguration<?> config = getDefinitionConfiguration();
    627        if (config.getMaxIndex(KEY_COMBINER) < 0) {
    628            // No combiner defined => set default
    629            result.setNodeCombiner(new OverrideCombiner());
    630        }
    631
    632        setUpCurrentParameters();
    633        initNodeCombinerListNodes(result, config, KEY_OVERRIDE_LIST);
    634        registerConfiguredProviders(config);
    635        setUpCurrentXMLParameters();
    636        currentXMLParameters.setFileSystem(initFileSystem(config));
    637        initSystemProperties(config, getBasePath());
    638        registerConfiguredLookups(config, result);
    639        configureEntityResolver(config, currentXMLParameters);
    640        setUpParentInterpolator(currentConfiguration, config);
    641
    642        final ConfigurationSourceData data = getSourceData();
    643        final boolean createBuilders = data.getChildBuilders().isEmpty();
    644        final List<ConfigurationBuilder<? extends Configuration>> overrideBuilders = data.createAndAddConfigurations(result, data.getOverrideSources(),
    645            data.overrideBuilders);
    646        if (createBuilders) {
    647            data.overrideBuilders.addAll(overrideBuilders);
    648        }
    649        if (!data.getUnionSources().isEmpty()) {
    650            final CombinedConfiguration addConfig = createAdditionalsConfiguration(result);
    651            result.addConfiguration(addConfig, ADDITIONAL_NAME);
    652            initNodeCombinerListNodes(addConfig, config, KEY_ADDITIONAL_LIST);
    653            final List<ConfigurationBuilder<? extends Configuration>> unionBuilders = data.createAndAddConfigurations(addConfig, data.unionDeclarations,
    654                data.unionBuilders);
    655            if (createBuilders) {
    656                data.unionBuilders.addAll(unionBuilders);
    657            }
    658        }
    659
    660        result.isEmpty(); // this sets up the node structure
    661        currentConfiguration = null;
    662    }
    663
    664    /**
    665     * Creates the {@code CombinedConfiguration} for the configuration sources in the {@code &lt;additional&gt;} section.
    666     * This method is called when the builder constructs the final configuration. It creates a new
    667     * {@code CombinedConfiguration} and initializes some properties from the result configuration.
    668     *
    669     * @param resultConfig the result configuration (this is the configuration that will be returned by the builder)
    670     * @return the {@code CombinedConfiguration} for the additional configuration sources
    671     * @since 1.7
    672     */
    673    protected CombinedConfiguration createAdditionalsConfiguration(final CombinedConfiguration resultConfig) {
    674        final CombinedConfiguration addConfig = new CombinedConfiguration(new UnionCombiner());
    675        addConfig.setListDelimiterHandler(resultConfig.getListDelimiterHandler());
    676        return addConfig;
    677    }
    678
    679    /**
    680     * Processes custom {@link Lookup} objects that might be declared in the definition configuration. Each {@code Lookup}
    681     * object is registered at the definition configuration and at the result configuration. It is also added to all child
    682     * configurations added to the resulting combined configuration.
    683     *
    684     * @param defConfig the definition configuration
    685     * @param resultConfig the resulting configuration
    686     * @throws ConfigurationException if an error occurs
    687     */
    688    protected void registerConfiguredLookups(final HierarchicalConfiguration<?> defConfig, final Configuration resultConfig) throws ConfigurationException {
    689        final Map<String, Lookup> lookups = defConfig.configurationsAt(KEY_CONFIGURATION_LOOKUPS).stream().collect(
    690                Collectors.toMap(config -> config.getString(KEY_LOOKUP_KEY), config -> (Lookup) fetchBeanHelper().createBean(new XMLBeanDeclaration(config))));
    691
    692        if (!lookups.isEmpty()) {
    693            final ConfigurationInterpolator defCI = defConfig.getInterpolator();
    694            if (defCI != null) {
    695                defCI.registerLookups(lookups);
    696            }
    697            resultConfig.getInterpolator().registerLookups(lookups);
    698        }
    699    }
    700
    701    /**
    702     * Creates and initializes a default {@code FileSystem} if the definition configuration contains a corresponding
    703     * declaration. The file system returned by this method is used as default for all file-based child configuration
    704     * sources.
    705     *
    706     * @param config the definition configuration
    707     * @return the default {@code FileSystem} (may be <b>null</b>)
    708     * @throws ConfigurationException if an error occurs
    709     */
    710    protected FileSystem initFileSystem(final HierarchicalConfiguration<?> config) throws ConfigurationException {
    711        if (config.getMaxIndex(FILE_SYSTEM) == 0) {
    712            final XMLBeanDeclaration decl = new XMLBeanDeclaration(config, FILE_SYSTEM);
    713            return (FileSystem) fetchBeanHelper().createBean(decl);
    714        }
    715        return null;
    716    }
    717
    718    /**
    719     * Handles a file with system properties that may be defined in the definition configuration. If such property file is
    720     * configured, all of its properties are added to the system properties.
    721     *
    722     * @param config the definition configuration
    723     * @param basePath the base path defined for this builder (may be <b>null</b>)
    724     * @throws ConfigurationException if an error occurs.
    725     */
    726    protected void initSystemProperties(final HierarchicalConfiguration<?> config, final String basePath) throws ConfigurationException {
    727        final String fileName = config.getString(KEY_SYSTEM_PROPS);
    728        if (fileName != null) {
    729            try {
    730                SystemConfiguration.setSystemProperties(basePath, fileName);
    731            } catch (final Exception ex) {
    732                throw new ConfigurationException("Error setting system properties from " + fileName, ex);
    733            }
    734        }
    735    }
    736
    737    /**
    738     * Creates and initializes a default {@code EntityResolver} if the definition configuration contains a corresponding
    739     * declaration.
    740     *
    741     * @param config the definition configuration
    742     * @param xmlParams the (already partly initialized) object with XML parameters; here the new resolver is to be stored
    743     * @throws ConfigurationException if an error occurs
    744     */
    745    protected void configureEntityResolver(final HierarchicalConfiguration<?> config, final XMLBuilderParametersImpl xmlParams) throws ConfigurationException {
    746        if (config.getMaxIndex(KEY_ENTITY_RESOLVER) == 0) {
    747            final XMLBeanDeclaration decl = new XMLBeanDeclaration(config, KEY_ENTITY_RESOLVER, true);
    748            final EntityResolver resolver = (EntityResolver) fetchBeanHelper().createBean(decl, CatalogResolver.class);
    749            final FileSystem fileSystem = xmlParams.getFileHandler().getFileSystem();
    750            if (fileSystem != null) {
    751                BeanHelper.setProperty(resolver, "fileSystem", fileSystem);
    752            }
    753            final String basePath = xmlParams.getFileHandler().getBasePath();
    754            if (basePath != null) {
    755                BeanHelper.setProperty(resolver, "baseDir", basePath);
    756            }
    757            final ConfigurationInterpolator ci = new ConfigurationInterpolator();
    758            ci.registerLookups(fetchPrefixLookups());
    759            BeanHelper.setProperty(resolver, "interpolator", ci);
    760
    761            xmlParams.setEntityResolver(resolver);
    762        }
    763    }
    764
    765    /**
    766     * Returns the {@code ConfigurationBuilderProvider} for the given tag. This method is called during creation of the
    767     * result configuration. (It is not allowed to call it at another point of time; result is then unpredictable!) It
    768     * supports all default providers and custom providers added through the parameters object as well.
    769     *
    770     * @param tagName the name of the tag
    771     * @return the provider that was registered for this tag or <b>null</b> if there is none
    772     */
    773    protected ConfigurationBuilderProvider providerForTag(final String tagName) {
    774        return currentParameters.providerForTag(tagName);
    775    }
    776
    777    /**
    778     * Initializes a parameters object for a child builder. This combined configuration builder has a bunch of properties
    779     * which may be inherited by child configurations, e.g. the base path, the file system, etc. While processing the
    780     * builders for child configurations, this method is called for each parameters object for a child builder. It
    781     * initializes some properties of the passed in parameters objects which are derived from this parent builder.
    782     *
    783     * @param params the parameters object to be initialized
    784     */
    785    protected void initChildBuilderParameters(final BuilderParameters params) {
    786        initDefaultChildParameters(params);
    787
    788        if (params instanceof BasicBuilderParameters) {
    789            initChildBasicParameters((BasicBuilderParameters) params);
    790        }
    791        if (params instanceof XMLBuilderProperties<?>) {
    792            initChildXMLParameters((XMLBuilderProperties<?>) params);
    793        }
    794        if (params instanceof FileBasedBuilderProperties<?>) {
    795            initChildFileBasedParameters((FileBasedBuilderProperties<?>) params);
    796        }
    797        if (params instanceof CombinedBuilderParametersImpl) {
    798            initChildCombinedParameters((CombinedBuilderParametersImpl) params);
    799        }
    800    }
    801
    802    /**
    803     * Initializes the event listeners of the specified builder from this object. This method is used to inherit all
    804     * listeners from a parent builder.
    805     *
    806     * @param dest the destination builder object which is to be initialized
    807     */
    808    void initChildEventListeners(final BasicConfigurationBuilder<? extends Configuration> dest) {
    809        copyEventListeners(dest);
    810    }
    811
    812    /**
    813     * Gets the configuration object that is currently constructed. This method can be called during construction of the
    814     * result configuration. It is intended for internal usage, e.g. some specialized builder providers need access to this
    815     * configuration to perform advanced initialization.
    816     *
    817     * @return the configuration that us currently under construction
    818     */
    819    CombinedConfiguration getConfigurationUnderConstruction() {
    820        return currentConfiguration;
    821    }
    822
    823    /**
    824     * Initializes a bean using the current {@code BeanHelper}. This is needed by builder providers when the configuration
    825     * objects for sub builders are constructed.
    826     *
    827     * @param bean the bean to be initialized
    828     * @param decl the {@code BeanDeclaration}
    829     */
    830    void initBean(final Object bean, final BeanDeclaration decl) {
    831        fetchBeanHelper().initBean(bean, decl);
    832    }
    833
    834    /**
    835     * Initializes the current parameters object. This object has either been passed at builder configuration time or it is
    836     * newly created. In any case, it is manipulated during result creation.
    837     */
    838    private void setUpCurrentParameters() {
    839        currentParameters = CombinedBuilderParametersImpl.fromParameters(getParameters(), true);
    840        currentParameters.registerMissingProviders(DEFAULT_PROVIDERS_MAP);
    841    }
    842
    843    /**
    844     * Sets up an XML parameters object which is used to store properties related to XML and file-based configurations
    845     * during creation of the result configuration. The properties stored in this object can be inherited to child
    846     * configurations.
    847     *
    848     * @throws ConfigurationException if an error occurs
    849     */
    850    private void setUpCurrentXMLParameters() throws ConfigurationException {
    851        currentXMLParameters = new XMLBuilderParametersImpl();
    852        initDefaultBasePath();
    853    }
    854
    855    /**
    856     * Sets up a parent {@code ConfigurationInterpolator} object. This object has a default {@link Lookup} querying the
    857     * resulting combined configuration. Thus interpolation works globally across all configuration sources.
    858     *
    859     * @param resultConfig the result configuration
    860     * @param defConfig the definition configuration
    861     */
    862    private void setUpParentInterpolator(final Configuration resultConfig, final Configuration defConfig) {
    863        parentInterpolator = new ConfigurationInterpolator();
    864        parentInterpolator.addDefaultLookup(new ConfigurationLookup(resultConfig));
    865        final ConfigurationInterpolator defInterpolator = defConfig.getInterpolator();
    866        if (defInterpolator != null) {
    867            defInterpolator.setParentInterpolator(parentInterpolator);
    868        }
    869    }
    870
    871    /**
    872     * Initializes the default base path for all file-based child configuration sources. The base path can be explicitly
    873     * defined in the parameters of this builder. Otherwise, if the definition builder is a file-based builder, it is
    874     * obtained from there.
    875     *
    876     * @throws ConfigurationException if an error occurs
    877     */
    878    private void initDefaultBasePath() throws ConfigurationException {
    879        assert currentParameters != null : "Current parameters undefined!";
    880        if (currentParameters.getBasePath() != null) {
    881            currentXMLParameters.setBasePath(currentParameters.getBasePath());
    882        } else {
    883            final ConfigurationBuilder<? extends HierarchicalConfiguration<?>> defBuilder = getDefinitionBuilder();
    884            if (defBuilder instanceof FileBasedConfigurationBuilder) {
    885                @SuppressWarnings("rawtypes")
    886                final FileBasedConfigurationBuilder fileBuilder = (FileBasedConfigurationBuilder) defBuilder;
    887                final URL url = fileBuilder.getFileHandler().getURL();
    888                currentXMLParameters.setBasePath(url != null ? url.toExternalForm() : fileBuilder.getFileHandler().getBasePath());
    889            }
    890        }
    891    }
    892
    893    /**
    894     * Executes the {@link org.apache.commons.configuration2.builder.DefaultParametersManager DefaultParametersManager}
    895     * stored in the current parameters on the passed in parameters object. If default handlers have been registered for
    896     * this type of parameters, an initialization is now performed. This method is called before the parameters object is
    897     * initialized from the configuration definition file. So default values can be overridden later with concrete property
    898     * definitions.
    899     *
    900     * @param params the parameters to be initialized
    901     * @throws org.apache.commons.configuration2.ex.ConfigurationRuntimeException if an error occurs when copying properties
    902     */
    903    private void initDefaultChildParameters(final BuilderParameters params) {
    904        currentParameters.getChildDefaultParametersManager().initializeParameters(params);
    905    }
    906
    907    /**
    908     * Initializes basic builder parameters for a child configuration with default settings set for this builder. This
    909     * implementation ensures that all {@code Lookup} objects are propagated to child configurations and interpolation is
    910     * setup correctly.
    911     *
    912     * @param params the parameters object
    913     */
    914    private void initChildBasicParameters(final BasicBuilderParameters params) {
    915        params.setPrefixLookups(fetchPrefixLookups());
    916        params.setParentInterpolator(parentInterpolator);
    917        if (currentParameters.isInheritSettings()) {
    918            params.inheritFrom(getParameters());
    919        }
    920    }
    921
    922    /**
    923     * Initializes a parameters object for a file-based configuration with properties already set for this parent builder.
    924     * This method handles properties like a default file system or a base path.
    925     *
    926     * @param params the parameters object
    927     */
    928    private void initChildFileBasedParameters(final FileBasedBuilderProperties<?> params) {
    929        params.setBasePath(getBasePath());
    930        params.setFileSystem(currentXMLParameters.getFileHandler().getFileSystem());
    931    }
    932
    933    /**
    934     * Initializes a parameters object for an XML configuration with properties already set for this parent builder.
    935     *
    936     * @param params the parameters object
    937     */
    938    private void initChildXMLParameters(final XMLBuilderProperties<?> params) {
    939        params.setEntityResolver(currentXMLParameters.getEntityResolver());
    940    }
    941
    942    /**
    943     * Initializes a parameters object for a combined configuration builder with properties already set for this parent
    944     * builder. This implementation deals only with a subset of properties. Other properties are already handled by the
    945     * specialized builder provider.
    946     *
    947     * @param params the parameters object
    948     */
    949    private void initChildCombinedParameters(final CombinedBuilderParametersImpl params) {
    950        params.registerMissingProviders(currentParameters);
    951        params.setBasePath(getBasePath());
    952    }
    953
    954    /**
    955     * Obtains the data object for the configuration sources and the corresponding builders. This object is created on first
    956     * access and reset when the definition builder sends a change event. This method is called in a synchronized block.
    957     *
    958     * @return the object with information about configuration sources
    959     * @throws ConfigurationException if an error occurs
    960     */
    961    private ConfigurationSourceData getSourceData() throws ConfigurationException {
    962        if (sourceData == null) {
    963            if (currentParameters == null) {
    964                setUpCurrentParameters();
    965                setUpCurrentXMLParameters();
    966            }
    967            sourceData = createSourceData();
    968        }
    969        return sourceData;
    970    }
    971
    972    /**
    973     * Creates the data object for configuration sources and the corresponding builders.
    974     *
    975     * @return the newly created data object
    976     * @throws ConfigurationException if an error occurs
    977     */
    978    private ConfigurationSourceData createSourceData() throws ConfigurationException {
    979        final ConfigurationSourceData result = new ConfigurationSourceData();
    980        result.initFromDefinitionConfiguration(getDefinitionConfiguration());
    981        return result;
    982    }
    983
    984    /**
    985     * Gets the current base path of this configuration builder. This is used for instance by all file-based child
    986     * configurations.
    987     *
    988     * @return the base path
    989     */
    990    private String getBasePath() {
    991        return currentXMLParameters.getFileHandler().getBasePath();
    992    }
    993
    994    /**
    995     * Registers providers defined in the configuration.
    996     *
    997     * @param defConfig the definition configuration
    998     */
    999    private void registerConfiguredProviders(final HierarchicalConfiguration<?> defConfig) {
    1000        defConfig.configurationsAt(KEY_CONFIGURATION_PROVIDERS).forEach(config -> {
    1001            final XMLBeanDeclaration decl = new XMLBeanDeclaration(config);
    1002            final String key = config.getString(KEY_PROVIDER_KEY);
    1003            currentParameters.registerProvider(key, (ConfigurationBuilderProvider) fetchBeanHelper().createBean(decl));
    1004        });
    1005    }
    1006
    1007    /**
    1008     * Adds a listener at the given definition builder which resets this builder when a reset of the definition builder
    1009     * happens. This way it is ensured that this builder produces a new combined configuration when its definition
    1010     * configuration changes.
    1011     *
    1012     * @param defBuilder the definition builder
    1013     */
    1014    private void addDefinitionBuilderChangeListener(final ConfigurationBuilder<? extends HierarchicalConfiguration<?>> defBuilder) {
    1015        defBuilder.addEventListener(ConfigurationBuilderEvent.RESET, event -> {
    1016            synchronized (this) {
    1017                reset();
    1018                definitionBuilder = defBuilder;
    1019            }
    1020        });
    1021    }
    1022
    1023    /**
    1024     * Returns a map with the current prefix lookup objects. This map is obtained from the {@code ConfigurationInterpolator}
    1025     * of the configuration under construction.
    1026     *
    1027     * @return the map with current prefix lookups (may be <b>null</b>)
    1028     */
    1029    private Map<String, ? extends Lookup> fetchPrefixLookups() {
    1030        final CombinedConfiguration cc = getConfigurationUnderConstruction();
    1031        return cc != null ? cc.getInterpolator().getLookups() : null;
    1032    }
    1033
    1034    /**
    1035     * Creates {@code ConfigurationDeclaration} objects for the specified configurations.
    1036     *
    1037     * @param configs the list with configurations
    1038     * @return a collection with corresponding declarations
    1039     */
    1040    private Collection<ConfigurationDeclaration> createDeclarations(final Collection<? extends HierarchicalConfiguration<?>> configs) {
    1041        return configs.stream().map(c -> new ConfigurationDeclaration(this, c)).collect(Collectors.toList());
    1042    }
    1043
    1044    /**
    1045     * Initializes the list nodes of the node combiner for the given combined configuration. This information can be set in
    1046     * the header section of the configuration definition file for both the override and the union combiners.
    1047     *
    1048     * @param cc the combined configuration to initialize
    1049     * @param defConfig the definition configuration
    1050     * @param key the key for the list nodes
    1051     */
    1052    private static void initNodeCombinerListNodes(final CombinedConfiguration cc, final HierarchicalConfiguration<?> defConfig, final String key) {
    1053        defConfig.getList(key).forEach(listNode -> cc.getNodeCombiner().addListNode((String) listNode));
    1054    }
    1055
    1056    /**
    1057     * Creates the map with the default configuration builder providers.
    1058     *
    1059     * @return the map with default providers
    1060     */
    1061    private static Map<String, ConfigurationBuilderProvider> createDefaultProviders() {
    1062        final Map<String, ConfigurationBuilderProvider> providers = new HashMap<>();
    1063        for (int i = 0; i < DEFAULT_TAGS.length; i++) {
    1064            providers.put(DEFAULT_TAGS[i], DEFAULT_PROVIDERS[i]);
    1065        }
    1066        return providers;
    1067    }
    1068
    1069    static {
    1070        DEFAULT_PROVIDERS_MAP = createDefaultProviders();
    1071    }
    1072
    1073    /**
    1074     * A data class for storing information about all configuration sources defined for a combined builder.
    1075     */
    1076    private final class ConfigurationSourceData {
    1077        /** A list with data for all builders for override configurations. */
    1078        private final List<ConfigurationDeclaration> overrideDeclarations;
    1079
    1080        /** A list with data for all builders for union configurations. */
    1081        private final List<ConfigurationDeclaration> unionDeclarations;
    1082
    1083        /** A list with the builders for override configurations. */
    1084        private final List<ConfigurationBuilder<? extends Configuration>> overrideBuilders;
    1085
    1086        /** A list with the builders for union configurations. */
    1087        private final List<ConfigurationBuilder<? extends Configuration>> unionBuilders;
    1088
    1089        /** A map for direct access to a builder by its name. */
    1090        private final Map<String, ConfigurationBuilder<? extends Configuration>> namedBuilders;
    1091
    1092        /** A collection with all child builders. */
    1093        private final Collection<ConfigurationBuilder<? extends Configuration>> allBuilders;
    1094
    1095        /** A listener for reacting on changes of sub builders. */
    1096        private final EventListener<ConfigurationBuilderEvent> changeListener;
    1097
    1098        /**
    1099         * Creates a new instance of {@code ConfigurationSourceData}.
    1100         */
    1101        public ConfigurationSourceData() {
    1102            overrideDeclarations = new ArrayList<>();
    1103            unionDeclarations = new ArrayList<>();
    1104            overrideBuilders = new ArrayList<>();
    1105            unionBuilders = new ArrayList<>();
    1106            namedBuilders = new HashMap<>();
    1107            allBuilders = new LinkedList<>();
    1108            changeListener = createBuilderChangeListener();
    1109        }
    1110
    1111        /**
    1112         * Initializes this object from the specified definition configuration.
    1113         *
    1114         * @param config the definition configuration
    1115         * @throws ConfigurationException if an error occurs
    1116         */
    1117        public void initFromDefinitionConfiguration(final HierarchicalConfiguration<?> config) throws ConfigurationException {
    1118            overrideDeclarations.addAll(createDeclarations(fetchTopLevelOverrideConfigs(config)));
    1119            overrideDeclarations.addAll(createDeclarations(config.childConfigurationsAt(KEY_OVERRIDE)));
    1120            unionDeclarations.addAll(createDeclarations(config.childConfigurationsAt(KEY_UNION)));
    1121        }
    1122
    1123        /**
    1124         * Processes the declaration of configuration builder providers, creates the corresponding builder if necessary, obtains
    1125         * configurations, and adds them to the specified result configuration.
    1126         *
    1127         * @param ccResult the result configuration
    1128         * @param srcDecl the collection with the declarations of configuration sources to process
    1129         * @return a list with configuration builders
    1130         * @throws ConfigurationException if an error occurs
    1131         */
    1132        public List<ConfigurationBuilder<? extends Configuration>> createAndAddConfigurations(final CombinedConfiguration ccResult,
    1133            final List<ConfigurationDeclaration> srcDecl, final List<ConfigurationBuilder<? extends Configuration>> builders) throws ConfigurationException {
    1134            final boolean createBuilders = builders.isEmpty();
    1135            final List<ConfigurationBuilder<? extends Configuration>> newBuilders;
    1136            if (createBuilders) {
    1137                newBuilders = new ArrayList<>(srcDecl.size());
    1138            } else {
    1139                newBuilders = builders;
    1140            }
    1141
    1142            for (int i = 0; i < srcDecl.size(); i++) {
    1143                final ConfigurationBuilder<? extends Configuration> b;
    1144                if (createBuilders) {
    1145                    b = createConfigurationBuilder(srcDecl.get(i));
    1146                    newBuilders.add(b);
    1147                } else {
    1148                    b = builders.get(i);
    1149                }
    1150                addChildConfiguration(ccResult, srcDecl.get(i), b);
    1151            }
    1152
    1153            return newBuilders;
    1154        }
    1155
    1156        /**
    1157         * Frees resources used by this object and performs clean up. This method is called when the owning builder is reset.
    1158         */
    1159        public void cleanUp() {
    1160            getChildBuilders().forEach(b -> b.removeEventListener(ConfigurationBuilderEvent.RESET, changeListener));
    1161            namedBuilders.clear();
    1162        }
    1163
    1164        /**
    1165         * Gets a collection containing the builders for all child configuration sources.
    1166         *
    1167         * @return the child configuration builders
    1168         */
    1169        public Collection<ConfigurationBuilder<? extends Configuration>> getChildBuilders() {
    1170            return allBuilders;
    1171        }
    1172
    1173        /**
    1174         * Gets a collection with all configuration source declarations defined in the override section.
    1175         *
    1176         * @return the override configuration builders
    1177         */
    1178        public List<ConfigurationDeclaration> getOverrideSources() {
    1179            return overrideDeclarations;
    1180        }
    1181
    1182        /**
    1183         * Gets a collection with all configuration source declarations defined in the union section.
    1184         *
    1185         * @return the union configuration builders
    1186         */
    1187        public List<ConfigurationDeclaration> getUnionSources() {
    1188            return unionDeclarations;
    1189        }
    1190
    1191        /**
    1192         * Gets the {@code ConfigurationBuilder} with the given name. If no such builder is defined in the definition
    1193         * configuration, result is <b>null</b>.
    1194         *
    1195         * @param name the name of the builder in question
    1196         * @return the builder with this name or <b>null</b>
    1197         */
    1198        public ConfigurationBuilder<? extends Configuration> getNamedBuilder(final String name) {
    1199            return namedBuilders.get(name);
    1200        }
    1201
    1202        /**
    1203         * Returns a set with the names of all known named builders.
    1204         *
    1205         * @return the names of the available sub builders
    1206         */
    1207        public Set<String> builderNames() {
    1208            return namedBuilders.keySet();
    1209        }
    1210
    1211        /**
    1212         * Creates a configuration builder based on a source declaration in the definition configuration.
    1213         *
    1214         * @param decl the current {@code ConfigurationDeclaration}
    1215         * @return the newly created builder
    1216         * @throws ConfigurationException if an error occurs
    1217         */
    1218        private ConfigurationBuilder<? extends Configuration> createConfigurationBuilder(final ConfigurationDeclaration decl) throws ConfigurationException {
    1219            final ConfigurationBuilderProvider provider = providerForTag(decl.getConfiguration().getRootElementName());
    1220            if (provider == null) {
    1221                throw new ConfigurationException("Unsupported configuration source: " + decl.getConfiguration().getRootElementName());
    1222            }
    1223
    1224            final ConfigurationBuilder<? extends Configuration> builder = provider.getConfigurationBuilder(decl);
    1225            if (decl.getName() != null) {
    1226                namedBuilders.put(decl.getName(), builder);
    1227            }
    1228            allBuilders.add(builder);
    1229            builder.addEventListener(ConfigurationBuilderEvent.RESET, changeListener);
    1230            return builder;
    1231        }
    1232
    1233        /**
    1234         * Creates a new configuration using the specified builder and adds it to the resulting combined configuration.
    1235         *
    1236         * @param ccResult the resulting combined configuration
    1237         * @param decl the current {@code ConfigurationDeclaration}
    1238         * @param builder the configuration builder
    1239         * @throws ConfigurationException if an error occurs
    1240         */
    1241        private void addChildConfiguration(final CombinedConfiguration ccResult, final ConfigurationDeclaration decl,
    1242            final ConfigurationBuilder<? extends Configuration> builder) throws ConfigurationException {
    1243            try {
    1244                ccResult.addConfiguration(builder.getConfiguration(), decl.getName(), decl.getAt());
    1245            } catch (final ConfigurationException cex) {
    1246                // ignore exceptions for optional configurations
    1247                if (!decl.isOptional()) {
    1248                    throw cex;
    1249                }
    1250            }
    1251        }
    1252
    1253        /**
    1254         * Creates a listener for builder change events. This listener is registered at all builders for child configurations.
    1255         */
    1256        private EventListener<ConfigurationBuilderEvent> createBuilderChangeListener() {
    1257            return event -> resetResult();
    1258        }
    1259
    1260        /**
    1261         * Finds the override configurations that are defined as top level elements in the configuration definition file. This
    1262         * method fetches the child elements of the root node and removes the nodes that represent other configuration sections.
    1263         * The remaining nodes are treated as definitions for override configurations.
    1264         *
    1265         * @param config the definition configuration
    1266         * @return a list with sub configurations for the top level override configurations
    1267         */
    1268        private List<? extends HierarchicalConfiguration<?>> fetchTopLevelOverrideConfigs(final HierarchicalConfiguration<?> config) {
    1269
    1270            final List<? extends HierarchicalConfiguration<?>> configs = config.childConfigurationsAt(null);
    1271            for (final Iterator<? extends HierarchicalConfiguration<?>> it = configs.iterator(); it.hasNext();) {
    1272                final String nodeName = it.next().getRootElementName();
    1273                for (final String element : CONFIG_SECTIONS) {
    1274                    if (element.equals(nodeName)) {
    1275                        it.remove();
    1276                        break;
    1277                    }
    1278                }
    1279            }
    1280            return configs;
    1281        }
    1282    }
    1283}