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;
029
030import org.apache.commons.configuration2.CombinedConfiguration;
031import org.apache.commons.configuration2.Configuration;
032import org.apache.commons.configuration2.ConfigurationLookup;
033import org.apache.commons.configuration2.HierarchicalConfiguration;
034import org.apache.commons.configuration2.SystemConfiguration;
035import org.apache.commons.configuration2.XMLConfiguration;
036import org.apache.commons.configuration2.beanutils.BeanDeclaration;
037import org.apache.commons.configuration2.beanutils.BeanHelper;
038import org.apache.commons.configuration2.beanutils.CombinedBeanDeclaration;
039import org.apache.commons.configuration2.beanutils.XMLBeanDeclaration;
040import org.apache.commons.configuration2.builder.BasicBuilderParameters;
041import org.apache.commons.configuration2.builder.BasicConfigurationBuilder;
042import org.apache.commons.configuration2.builder.BuilderParameters;
043import org.apache.commons.configuration2.builder.ConfigurationBuilder;
044import org.apache.commons.configuration2.builder.ConfigurationBuilderEvent;
045import org.apache.commons.configuration2.builder.FileBasedBuilderParametersImpl;
046import org.apache.commons.configuration2.builder.FileBasedBuilderProperties;
047import org.apache.commons.configuration2.builder.FileBasedConfigurationBuilder;
048import org.apache.commons.configuration2.builder.XMLBuilderParametersImpl;
049import org.apache.commons.configuration2.builder.XMLBuilderProperties;
050import org.apache.commons.configuration2.event.EventListener;
051import org.apache.commons.configuration2.ex.ConfigurationException;
052import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
053import org.apache.commons.configuration2.interpol.Lookup;
054import org.apache.commons.configuration2.io.FileSystem;
055import org.apache.commons.configuration2.resolver.CatalogResolver;
056import org.apache.commons.configuration2.tree.DefaultExpressionEngineSymbols;
057import org.apache.commons.configuration2.tree.OverrideCombiner;
058import org.apache.commons.configuration2.tree.UnionCombiner;
059import org.xml.sax.EntityResolver;
060
061/**
062 * <p>
063 * A specialized {@code ConfigurationBuilder} implementation that creates a
064 * {@link CombinedConfiguration} from multiple configuration sources defined by
065 * an XML-based <em>configuration definition file</em>.
066 * </p>
067 * <p>
068 * This class provides an easy and flexible means for loading multiple
069 * configuration sources and combining the results into a single configuration
070 * object. The sources to be loaded are defined in an XML document that can
071 * contain certain tags representing the different supported configuration
072 * classes. If such a tag is found, a corresponding {@code ConfigurationBuilder}
073 * class is instantiated and initialized using the classes of the
074 * {@code beanutils} package (namely
075 * {@link org.apache.commons.configuration2.beanutils.XMLBeanDeclaration
076 * XMLBeanDeclaration} will be used to extract the configuration's
077 * initialization parameters, which allows for complex initialization
078 * scenarios).
079 * </p>
080 * <p>
081 * It is also possible to add custom tags to the configuration definition file.
082 * For this purpose an implementation of
083 * {@link CombinedConfigurationBuilderProvider} has to be created which is
084 * responsible for the creation of a {@code ConfigurationBuilder} associated
085 * with the custom tag. An instance of this class has to be registered at the
086 * {@link CombinedBuilderParametersImpl} object which is used to initialize this
087 * {@code CombinedConfigurationBuilder}. This provider will then be called when
088 * the corresponding custom tag is detected. For many default configuration
089 * classes providers are already registered.
090 * </p>
091 * <p>
092 * The configuration definition file has the following basic structure:
093 * </p>
094 *
095 * <pre>
096 * &lt;configuration systemProperties="properties file name"&gt;
097 *   &lt;header&gt;
098 *     &lt;!-- Optional meta information about the combined configuration --&gt;
099 *   &lt;/header&gt;
100 *   &lt;override&gt;
101 *     &lt;!-- Declarations for override configurations --&gt;
102 *   &lt;/override&gt;
103 *   &lt;additional&gt;
104 *     &lt;!-- Declarations for union configurations --&gt;
105 *   &lt;/additional&gt;
106 * &lt;/configuration&gt;
107 * </pre>
108 *
109 * <p>
110 * The name of the root element (here {@code configuration}) is arbitrary. The
111 * optional {@code systemProperties} attribute identifies the path to a property
112 * file containing properties that should be added to the system properties. If
113 * specified on the root element, the system properties are set before the rest
114 * of the configuration is processed.
115 * </p>
116 * <p>
117 * There are two sections (both of them are optional) for declaring
118 * <em>override</em> and <em>additional</em> configurations. Configurations in
119 * the former section are evaluated in the order of their declaration, and
120 * properties of configurations declared earlier hide those of configurations
121 * declared later. Configurations in the latter section are combined to a union
122 * configuration, i.e. all of their properties are added to a large hierarchical
123 * configuration. Configuration declarations that occur as direct children of
124 * the root element are treated as override declarations.
125 * </p>
126 * <p>
127 * Each configuration declaration consists of a tag whose name is associated
128 * with a {@code CombinedConfigurationBuilderProvider}. This can be one of the
129 * predefined tags like {@code properties}, or {@code xml}, or a custom tag, for
130 * which a configuration builder provider was registered (as described above).
131 * Attributes and sub elements with specific initialization parameters can be
132 * added. There are some reserved attributes with a special meaning that can be
133 * used in every configuration declaration:
134 * </p>
135 * <table border="1">
136 * <caption>Standard attributes for configuration declarations</caption>
137 * <tr>
138 * <th>Attribute</th>
139 * <th>Meaning</th>
140 * </tr>
141 * <tr>
142 * <td valign="top">{@code config-name}</td>
143 * <td>Allows specifying a name for this configuration. This name can be used to
144 * obtain a reference to the configuration from the resulting combined
145 * configuration (see below). It can also be passed to the
146 * {@link #getNamedBuilder(String)} method.</td>
147 * </tr>
148 * <tr>
149 * <td valign="top">{@code config-at}</td>
150 * <td>With this attribute an optional prefix can be specified for the
151 * properties of the corresponding configuration.</td>
152 * </tr>
153 * <tr>
154 * <td valign="top">{@code config-optional}</td>
155 * <td>Declares a configuration source as optional. This means that errors that
156 * occur when creating the configuration are ignored.</td>
157 * </tr>
158 * <tr>
159 * <td valign="top">{@code config-reload}</td>
160 * <td>Many configuration sources support a reloading mechanism. For those
161 * sources it is possible to enable reloading by providing this attribute with a
162 * value of <strong>true</strong>.</td>
163 * </tr>
164 * </table>
165 * <p>
166 * The optional <em>header</em> section can contain some meta data about the
167 * created configuration itself. For instance, it is possible to set further
168 * properties of the {@code NodeCombiner} objects used for constructing the
169 * resulting configuration.
170 * </p>
171 * <p>
172 * The default configuration object returned by this builder is an instance of
173 * the {@link CombinedConfiguration} class. This allows for convenient access to
174 * the configuration objects maintained by the combined configuration (e.g. for
175 * updates of single configuration objects). It has also the advantage that the
176 * properties stored in all declared configuration objects are collected and
177 * transformed into a single hierarchical structure, which can be accessed using
178 * different expression engines. The actual {@code CombinedConfiguration}
179 * implementation can be overridden by specifying the class in the
180 * <em>config-class</em> attribute of the result element.
181 * </p>
182 * <p>
183 * A custom EntityResolver can be used for all XMLConfigurations by adding
184 * </p>
185 *
186 * <pre>
187 * &lt;entity-resolver config-class="EntityResolver fully qualified class name"&gt;
188 * </pre>
189 *
190 * <p>
191 * A specific CatalogResolver can be specified for all XMLConfiguration sources
192 * by adding
193 * </p>
194 * <pre>
195 * &lt;entity-resolver catalogFiles="comma separated list of catalog files"&gt;
196 * </pre>
197 *
198 * <p>
199 * Additional ConfigurationProviders can be added by configuring them in the
200 * <em>header</em> section.
201 * </p>
202 *
203 * <pre>
204 * &lt;providers&gt;
205 *   &lt;provider config-tag="tag name" config-class="provider fully qualified class name"/&gt;
206 * &lt;/providers&gt;
207 * </pre>
208 *
209 * <p>
210 * Additional variable resolvers can be added by configuring them in the
211 * <em>header</em> section.
212 * </p>
213 *
214 * <pre>
215 * &lt;lookups&gt;
216 *   &lt;lookup config-prefix="prefix" config-class="StrLookup fully qualified class name"/&gt;
217 * &lt;/lookups&gt;
218 * </pre>
219 *
220 * <p>
221 * All declared override configurations are directly added to the resulting
222 * combined configuration. If they are given names (using the
223 * {@code config-name} attribute), they can directly be accessed using the
224 * {@code getConfiguration(String)} method of {@code CombinedConfiguration}. The
225 * additional configurations are altogether added to another combined
226 * configuration, which uses a union combiner. Then this union configuration is
227 * added to the resulting combined configuration under the name defined by the
228 * {@code ADDITIONAL_NAME} constant. The {@link #getNamedBuilder(String)} method
229 * can be used to access the {@code ConfigurationBuilder} objects for all
230 * configuration sources which have been assigned a name; care has to be taken
231 * that these names are unique.
232 * </p>
233 *
234 * @since 1.3
235 * @author <a
236 *         href="http://commons.apache.org/configuration/team-list.html">Commons
237 *         Configuration team</a>
238 * @version $Id: CombinedConfigurationBuilder.java 1836754 2018-07-26 19:39:33Z oheger $
239 */
240public class CombinedConfigurationBuilder extends BasicConfigurationBuilder<CombinedConfiguration>
241{
242    /**
243     * Constant for the name of the additional configuration. If the
244     * configuration definition file contains an {@code additional}
245     * section, a special union configuration is created and added under this
246     * name to the resulting combined configuration.
247     */
248    public static final String ADDITIONAL_NAME = CombinedConfigurationBuilder.class
249            .getName()
250            + "/ADDITIONAL_CONFIG";
251
252    /** Constant for the name of the configuration bean factory. */
253    static final String CONFIG_BEAN_FACTORY_NAME = CombinedConfigurationBuilder.class
254            .getName()
255            + ".CONFIG_BEAN_FACTORY_NAME";
256
257    /** Constant for the reserved name attribute. */
258    static final String ATTR_NAME = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START
259            + XMLBeanDeclaration.RESERVED_PREFIX
260            + "name"
261            + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
262
263    /** Constant for the name of the at attribute. */
264    static final String ATTR_ATNAME = "at";
265
266    /** Constant for the reserved at attribute. */
267    static final String ATTR_AT_RES = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START
268            + XMLBeanDeclaration.RESERVED_PREFIX
269            + ATTR_ATNAME
270            + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
271
272    /** Constant for the at attribute without the reserved prefix. */
273    static final String ATTR_AT = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START
274            + ATTR_ATNAME + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
275
276    /** Constant for the name of the optional attribute. */
277    static final String ATTR_OPTIONALNAME = "optional";
278
279    /** Constant for the reserved optional attribute. */
280    static final String ATTR_OPTIONAL_RES = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START
281            + XMLBeanDeclaration.RESERVED_PREFIX
282            + ATTR_OPTIONALNAME
283            + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
284
285    /** Constant for the optional attribute without the reserved prefix. */
286    static final String ATTR_OPTIONAL = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START
287            + ATTR_OPTIONALNAME + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
288
289    /** Constant for the forceCreate attribute. */
290    static final String ATTR_FORCECREATE = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START
291            + XMLBeanDeclaration.RESERVED_PREFIX
292            + "forceCreate"
293            + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
294
295    /** Constant for the reload attribute. */
296    static final String ATTR_RELOAD = DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_START
297            + XMLBeanDeclaration.RESERVED_PREFIX
298            + "reload"
299            + DefaultExpressionEngineSymbols.DEFAULT_ATTRIBUTE_END;
300
301    /**
302     * Constant for the tag attribute for providers.
303     */
304    static final String KEY_SYSTEM_PROPS = "[@systemProperties]";
305
306    /** Constant for the name of the header section. */
307    static final String SEC_HEADER = "header";
308
309    /** Constant for an expression that selects the union configurations. */
310    static final String KEY_UNION = "additional";
311
312    /** An array with the names of top level configuration sections.*/
313    static final String[] CONFIG_SECTIONS = {
314        "additional", "override", SEC_HEADER
315    };
316
317    /**
318     * Constant for an expression that selects override configurations in the
319     * override section.
320     */
321    static final String KEY_OVERRIDE = "override";
322
323    /**
324     * Constant for the key that points to the list nodes definition of the
325     * override combiner.
326     */
327    static final String KEY_OVERRIDE_LIST = SEC_HEADER
328            + ".combiner.override.list-nodes.node";
329
330    /**
331     * Constant for the key that points to the list nodes definition of the
332     * additional combiner.
333     */
334    static final String KEY_ADDITIONAL_LIST = SEC_HEADER
335            + ".combiner.additional.list-nodes.node";
336
337    /**
338     * Constant for the key for defining providers in the configuration file.
339     */
340    static final String KEY_CONFIGURATION_PROVIDERS = SEC_HEADER
341            + ".providers.provider";
342
343    /**
344     * Constant for the tag attribute for providers.
345     */
346    static final String KEY_PROVIDER_KEY = XMLBeanDeclaration.ATTR_PREFIX + "tag]";
347
348    /**
349     * Constant for the key for defining variable resolvers
350     */
351    static final String KEY_CONFIGURATION_LOOKUPS = SEC_HEADER
352            + ".lookups.lookup";
353
354    /**
355     * Constant for the key for defining entity resolvers
356     */
357    static final String KEY_ENTITY_RESOLVER = SEC_HEADER + ".entity-resolver";
358
359    /**
360     * Constant for the prefix attribute for lookups.
361     */
362    static final String KEY_LOOKUP_KEY = XMLBeanDeclaration.ATTR_PREFIX + "prefix]";
363
364    /**
365     * Constant for the FileSystem.
366     */
367    static final String FILE_SYSTEM = SEC_HEADER + ".fileSystem";
368
369    /**
370     * Constant for the key of the result declaration. This key can point to a
371     * bean declaration, which defines properties of the resulting combined
372     * configuration.
373     */
374    static final String KEY_RESULT = SEC_HEADER + ".result";
375
376    /** Constant for the key of the combiner in the result declaration.*/
377    static final String KEY_COMBINER = KEY_RESULT + ".nodeCombiner";
378
379    /** Constant for the XML file extension. */
380    static final String EXT_XML = "xml";
381
382    /** Constant for the basic configuration builder class. */
383    private static final String BASIC_BUILDER =
384            "org.apache.commons.configuration2.builder.BasicConfigurationBuilder";
385
386    /** Constant for the file-based configuration builder class. */
387    private static final String FILE_BUILDER =
388            "org.apache.commons.configuration2.builder.FileBasedConfigurationBuilder";
389
390    /** Constant for the reloading file-based configuration builder class. */
391    private static final String RELOADING_BUILDER =
392            "org.apache.commons.configuration2.builder.ReloadingFileBasedConfigurationBuilder";
393
394    /** Constant for the name of the file-based builder parameters class. */
395    private static final String FILE_PARAMS =
396            "org.apache.commons.configuration2.builder.FileBasedBuilderParametersImpl";
397
398    /** Constant for the provider for properties files. */
399    private static final ConfigurationBuilderProvider PROPERTIES_PROVIDER =
400            new FileExtensionConfigurationBuilderProvider(
401                    FILE_BUILDER,
402                    RELOADING_BUILDER,
403                    "org.apache.commons.configuration2.XMLPropertiesConfiguration",
404                    "org.apache.commons.configuration2.PropertiesConfiguration",
405                    EXT_XML, Collections.singletonList(FILE_PARAMS));
406
407    /** Constant for the provider for XML files. */
408    private static final ConfigurationBuilderProvider XML_PROVIDER =
409            new BaseConfigurationBuilderProvider(FILE_BUILDER, RELOADING_BUILDER,
410                    "org.apache.commons.configuration2.XMLConfiguration",
411                    Collections.singletonList("org.apache.commons.configuration2.builder.XMLBuilderParametersImpl"));
412
413    /** Constant for the provider for JNDI sources. */
414    private static final BaseConfigurationBuilderProvider JNDI_PROVIDER =
415            new BaseConfigurationBuilderProvider(
416                    BASIC_BUILDER,
417                    null,
418                    "org.apache.commons.configuration2.JNDIConfiguration",
419                    Collections.singletonList("org.apache.commons.configuration2.builder.JndiBuilderParametersImpl"));
420
421    /** Constant for the provider for system properties. */
422    private static final BaseConfigurationBuilderProvider SYSTEM_PROVIDER =
423            new BaseConfigurationBuilderProvider(
424                    BASIC_BUILDER,
425                    null,
426                    "org.apache.commons.configuration2.SystemConfiguration",
427                    Collections.singletonList("org.apache.commons.configuration2.builder.BasicBuilderParameters"));
428
429    /** Constant for the provider for ini files. */
430    private static final BaseConfigurationBuilderProvider INI_PROVIDER =
431            new BaseConfigurationBuilderProvider(FILE_BUILDER, RELOADING_BUILDER,
432                    "org.apache.commons.configuration2.INIConfiguration",
433                    Collections.singletonList(FILE_PARAMS));
434
435    /** Constant for the provider for environment properties. */
436    private static final BaseConfigurationBuilderProvider ENV_PROVIDER =
437            new BaseConfigurationBuilderProvider(
438                    BASIC_BUILDER,
439                    null,
440                    "org.apache.commons.configuration2.EnvironmentConfiguration",
441                    Collections.singletonList("org.apache.commons.configuration2.builder.BasicBuilderParameters"));
442
443    /** Constant for the provider for plist files. */
444    private static final BaseConfigurationBuilderProvider PLIST_PROVIDER =
445            new FileExtensionConfigurationBuilderProvider(
446                    FILE_BUILDER,
447                    RELOADING_BUILDER,
448                    "org.apache.commons.configuration2.plist.XMLPropertyListConfiguration",
449                    "org.apache.commons.configuration2.plist.PropertyListConfiguration",
450                    EXT_XML, Collections.singletonList(FILE_PARAMS));
451
452    /** Constant for the provider for configuration definition files. */
453    private static final BaseConfigurationBuilderProvider COMBINED_PROVIDER =
454            new CombinedConfigurationBuilderProvider();
455
456    /** Constant for the provider for multiple XML configurations. */
457    private static final MultiFileConfigurationBuilderProvider MULTI_XML_PROVIDER =
458            new MultiFileConfigurationBuilderProvider(
459                    "org.apache.commons.configuration2.XMLConfiguration",
460                    "org.apache.commons.configuration2.builder.XMLBuilderParametersImpl");
461
462    /** An array with the names of the default tags. */
463    private static final String[] DEFAULT_TAGS = {
464            "properties", "xml", "hierarchicalXml", "plist",
465            "ini", "system", "env", "jndi", "configuration", "multiFile"
466    };
467
468    /** An array with the providers for the default tags. */
469    private static final ConfigurationBuilderProvider[] DEFAULT_PROVIDERS = {
470            PROPERTIES_PROVIDER, XML_PROVIDER, XML_PROVIDER, PLIST_PROVIDER, INI_PROVIDER,
471            SYSTEM_PROVIDER, ENV_PROVIDER, JNDI_PROVIDER, COMBINED_PROVIDER,
472            MULTI_XML_PROVIDER
473    };
474
475    /** A map with the default configuration builder providers. */
476    private static final Map<String, ConfigurationBuilderProvider> DEFAULT_PROVIDERS_MAP;
477
478    /** The builder for the definition configuration. */
479    private ConfigurationBuilder<? extends HierarchicalConfiguration<?>> definitionBuilder;
480
481    /** Stores temporarily the configuration with the builder definitions. */
482    private HierarchicalConfiguration<?> definitionConfiguration;
483
484    /** The object with data about configuration sources. */
485    private ConfigurationSourceData sourceData;
486
487    /** Stores the current parameters object. */
488    private CombinedBuilderParametersImpl currentParameters;
489
490    /** The current XML parameters object. */
491    private XMLBuilderParametersImpl currentXMLParameters;
492
493    /** The configuration that is currently constructed. */
494    private CombinedConfiguration currentConfiguration;
495
496    /**
497     * A {@code ConfigurationInterpolator} to be used as parent for all child
498     * configurations to enable cross-source interpolation.
499     */
500    private ConfigurationInterpolator parentInterpolator;
501
502    /**
503     * Creates a new instance of {@code CombinedConfigurationBuilder}. No parameters
504     * are set.
505     */
506    public CombinedConfigurationBuilder()
507    {
508        super(CombinedConfiguration.class);
509    }
510
511    /**
512     *
513     * Creates a new instance of {@code CombinedConfigurationBuilder} and sets
514     * the specified initialization parameters.
515     * @param params a map with initialization parameters
516     */
517    public CombinedConfigurationBuilder(Map<String, Object> params)
518    {
519        super(CombinedConfiguration.class, params);
520    }
521
522    /**
523     *
524     * Creates a new instance of {@code CombinedConfigurationBuilder} and sets
525     * the specified initialization parameters and the <em>allowFailOnInit</em> flag.
526     * @param params a map with initialization parameters
527     * @param allowFailOnInit the <em>allowFailOnInit</em> flag
528     */
529    public CombinedConfigurationBuilder(Map<String, Object> params, boolean allowFailOnInit)
530    {
531        super(CombinedConfiguration.class, params, allowFailOnInit);
532    }
533
534    /**
535     * Returns the {@code ConfigurationBuilder} which creates the definition
536     * configuration.
537     *
538     * @return the builder for the definition configuration
539     * @throws ConfigurationException if an error occurs
540     */
541    public synchronized ConfigurationBuilder<? extends HierarchicalConfiguration<?>> getDefinitionBuilder()
542            throws ConfigurationException
543    {
544        if (definitionBuilder == null)
545        {
546            definitionBuilder = setupDefinitionBuilder(getParameters());
547            addDefinitionBuilderChangeListener(definitionBuilder);
548        }
549        return definitionBuilder;
550    }
551
552    /**
553     * {@inheritDoc} This method is overridden to adapt the return type.
554     */
555    @Override
556    public CombinedConfigurationBuilder configure(BuilderParameters... params)
557    {
558        super.configure(params);
559        return this;
560    }
561
562    /**
563     * <p>
564     * Returns the configuration builder with the given name. With this method a
565     * builder of a child configuration which was given a name in the
566     * configuration definition file can be accessed directly.
567     * </p>
568     * <p>
569     * <strong>Important note:</strong> This method only returns a meaningful
570     * result after the result configuration has been created by calling
571     * {@code getConfiguration()}. If called before, always an exception is
572     * thrown.
573     * </p>
574     *
575     * @param name the name of the builder in question
576     * @return the child configuration builder with this name
577     * @throws ConfigurationException if information about named builders is not
578     *         yet available or no builder with this name exists
579     */
580    public synchronized ConfigurationBuilder<? extends Configuration> getNamedBuilder(
581            String name) throws ConfigurationException
582    {
583        if (sourceData == null)
584        {
585            throw new ConfigurationException("Information about child builders"
586                    + " has not been setup yet! Call getConfiguration() first.");
587        }
588        ConfigurationBuilder<? extends Configuration> builder =
589                sourceData.getNamedBuilder(name);
590        if (builder == null)
591        {
592            throw new ConfigurationException("Builder cannot be resolved: "
593                    + name);
594        }
595        return builder;
596    }
597
598    /**
599     * <p>
600     * Returns a set with the names of all child configuration builders. A tag
601     * defining a configuration source in the configuration definition file can
602     * have the {@code config-name} attribute. If this attribute is present, the
603     * corresponding builder is assigned this name and can be directly accessed
604     * through the {@link #getNamedBuilder(String)} method. This method returns
605     * a collection with all available builder names.
606     * </p>
607     * <p>
608     * <strong>Important note:</strong> This method only returns a meaningful
609     * result after the result configuration has been created by calling
610     * {@code getConfiguration()}. If called before, always an empty set is
611     * returned.
612     * </p>
613     *
614     * @return a set with the names of all builders
615     */
616    public synchronized Set<String> builderNames()
617    {
618        if (sourceData == null)
619        {
620            return Collections.emptySet();
621        }
622        else
623        {
624            return Collections.unmodifiableSet(sourceData.builderNames());
625        }
626    }
627
628    /**
629     * {@inheritDoc} This implementation resets some specific internal state of
630     * this builder.
631     */
632    @Override
633    public synchronized void resetParameters()
634    {
635        super.resetParameters();
636        definitionBuilder = null;
637        definitionConfiguration = null;
638        currentParameters = null;
639        currentXMLParameters = null;
640
641        if (sourceData != null)
642        {
643            sourceData.cleanUp();
644            sourceData = null;
645        }
646    }
647
648    /**
649     * Obtains the {@code ConfigurationBuilder} object which provides access to
650     * the configuration containing the definition of the combined configuration
651     * to create. If a definition builder is defined in the parameters, it is
652     * used. Otherwise, we check whether the combined builder parameters object
653     * contains a parameters object for the definition builder. If this is the
654     * case, a builder for an {@code XMLConfiguration} is created and configured
655     * with this object. As a last resort, it is looked for a
656     * {@link FileBasedBuilderParametersImpl} object in the properties. If
657     * found, also a XML configuration builder is created which loads this file.
658     * Note: This method is called from a synchronized block.
659     *
660     * @param params the current parameters for this builder
661     * @return the builder for the definition configuration
662     * @throws ConfigurationException if an error occurs
663     */
664    protected ConfigurationBuilder<? extends HierarchicalConfiguration<?>> setupDefinitionBuilder(
665            Map<String, Object> params) throws ConfigurationException
666    {
667        CombinedBuilderParametersImpl cbParams =
668                CombinedBuilderParametersImpl.fromParameters(params);
669        if (cbParams != null)
670        {
671            ConfigurationBuilder<? extends HierarchicalConfiguration<?>> defBuilder =
672                    cbParams.getDefinitionBuilder();
673            if (defBuilder != null)
674            {
675                return defBuilder;
676            }
677
678            if (cbParams.getDefinitionBuilderParameters() != null)
679            {
680                return createXMLDefinitionBuilder(cbParams
681                        .getDefinitionBuilderParameters());
682            }
683        }
684
685        BuilderParameters fileParams =
686                FileBasedBuilderParametersImpl.fromParameters(params);
687        if (fileParams != null)
688        {
689            return createXMLDefinitionBuilder(fileParams);
690        }
691
692        throw new ConfigurationException(
693                "No builder for configuration definition specified!");
694    }
695
696    /**
697     * Creates a default builder for the definition configuration and
698     * initializes it with a parameters object. This method is called if no
699     * definition builder is defined in this builder's parameters. This
700     * implementation creates a default file-based builder which produces an
701     * {@code XMLConfiguration}; it expects a corresponding file specification.
702     * Note: This method is called in a synchronized block.
703     *
704     * @param builderParams the parameters object for the builder
705     * @return the standard builder for the definition configuration
706     */
707    protected ConfigurationBuilder<? extends HierarchicalConfiguration<?>> createXMLDefinitionBuilder(
708            BuilderParameters builderParams)
709    {
710        return new FileBasedConfigurationBuilder<>(
711                XMLConfiguration.class).configure(builderParams);
712    }
713
714    /**
715     * Returns the configuration containing the definition of the combined
716     * configuration to be created. This method only returns a defined result
717     * during construction of the result configuration. The definition
718     * configuration is obtained from the definition builder at first access and
719     * then stored temporarily to ensure that during result construction always
720     * the same configuration instance is used. (Otherwise, it would be possible
721     * that the definition builder returns a different instance when queried
722     * multiple times.)
723     *
724     * @return the definition configuration
725     * @throws ConfigurationException if an error occurs
726     */
727    protected HierarchicalConfiguration<?> getDefinitionConfiguration()
728            throws ConfigurationException
729    {
730        if (definitionConfiguration == null)
731        {
732            definitionConfiguration = getDefinitionBuilder().getConfiguration();
733        }
734        return definitionConfiguration;
735    }
736
737    /**
738     * Returns a collection with the builders for all child configuration
739     * sources. This method can be used by derived classes providing additional
740     * functionality on top of the declared configuration sources. It only
741     * returns a defined value during construction of the result configuration
742     * instance.
743     *
744     * @return a collection with the builders for child configuration sources
745     */
746    protected synchronized Collection<ConfigurationBuilder<? extends Configuration>> getChildBuilders()
747    {
748        return sourceData.getChildBuilders();
749    }
750
751    /**
752     * {@inheritDoc} This implementation evaluates the {@code result} property
753     * of the definition configuration. It creates a combined bean declaration
754     * with both the properties specified in the definition file and the
755     * properties defined as initialization parameters.
756     */
757    @Override
758    protected BeanDeclaration createResultDeclaration(Map<String, Object> params)
759            throws ConfigurationException
760    {
761        BeanDeclaration paramsDecl = super.createResultDeclaration(params);
762        XMLBeanDeclaration resultDecl =
763                new XMLBeanDeclaration(getDefinitionConfiguration(),
764                        KEY_RESULT, true, CombinedConfiguration.class.getName());
765        return new CombinedBeanDeclaration(resultDecl, paramsDecl);
766    }
767
768    /**
769     * {@inheritDoc} This implementation processes the definition configuration
770     * in order to
771     * <ul>
772     * <li>initialize the resulting {@code CombinedConfiguration}</li>
773     * <li>determine the builders for all configuration sources</li>
774     * <li>populate the resulting {@code CombinedConfiguration}</li>
775     * </ul>
776     */
777    @Override
778    protected void initResultInstance(CombinedConfiguration result)
779            throws ConfigurationException
780    {
781        super.initResultInstance(result);
782
783        currentConfiguration = result;
784        HierarchicalConfiguration<?> config = getDefinitionConfiguration();
785        if (config.getMaxIndex(KEY_COMBINER) < 0)
786        {
787            // No combiner defined => set default
788            result.setNodeCombiner(new OverrideCombiner());
789        }
790
791        setUpCurrentParameters();
792        initNodeCombinerListNodes(result, config, KEY_OVERRIDE_LIST);
793        registerConfiguredProviders(config);
794        setUpCurrentXMLParameters();
795        currentXMLParameters.setFileSystem(initFileSystem(config));
796        initSystemProperties(config, getBasePath());
797        registerConfiguredLookups(config, result);
798        configureEntityResolver(config, currentXMLParameters);
799        setUpParentInterpolator(currentConfiguration, config);
800
801        ConfigurationSourceData data = getSourceData();
802        boolean createBuilders = data.getChildBuilders().isEmpty();
803        List<ConfigurationBuilder<? extends Configuration>> overrideBuilders =
804                data.createAndAddConfigurations(result,
805                        data.getOverrideSources(), data.overrideBuilders);
806        if (createBuilders)
807        {
808            data.overrideBuilders.addAll(overrideBuilders);
809        }
810        if (!data.getUnionSources().isEmpty())
811        {
812            CombinedConfiguration addConfig = createAdditionalsConfiguration(result);
813            result.addConfiguration(addConfig, ADDITIONAL_NAME);
814            initNodeCombinerListNodes(addConfig, config, KEY_ADDITIONAL_LIST);
815            List<ConfigurationBuilder<? extends Configuration>> unionBuilders =
816                    data.createAndAddConfigurations(addConfig,
817                            data.unionDeclarations, data.unionBuilders);
818            if (createBuilders)
819            {
820                data.unionBuilders.addAll(unionBuilders);
821            }
822        }
823
824        result.isEmpty();  // this sets up the node structure
825        currentConfiguration = null;
826    }
827
828    /**
829     * Creates the {@code CombinedConfiguration} for the configuration
830     * sources in the <code>&lt;additional&gt;</code> section. This method is
831     * called when the builder constructs the final configuration. It creates a
832     * new {@code CombinedConfiguration} and initializes some properties
833     * from the result configuration.
834     *
835     * @param resultConfig the result configuration (this is the configuration
836     *        that will be returned by the builder)
837     * @return the {@code CombinedConfiguration} for the additional
838     *         configuration sources
839     * @since 1.7
840     */
841    protected CombinedConfiguration createAdditionalsConfiguration(
842            CombinedConfiguration resultConfig)
843    {
844        CombinedConfiguration addConfig =
845                new CombinedConfiguration(new UnionCombiner());
846        addConfig.setListDelimiterHandler(resultConfig.getListDelimiterHandler());
847        return addConfig;
848    }
849
850    /**
851     * Processes custom {@link Lookup} objects that might be declared in the
852     * definition configuration. Each {@code Lookup} object is registered at the
853     * definition configuration and at the result configuration. It is also
854     * added to all child configurations added to the resulting combined
855     * configuration.
856     *
857     * @param defConfig the definition configuration
858     * @param resultConfig the resulting configuration
859     * @throws ConfigurationException if an error occurs
860     */
861    protected void registerConfiguredLookups(
862            HierarchicalConfiguration<?> defConfig, Configuration resultConfig)
863            throws ConfigurationException
864    {
865        Map<String, Lookup> lookups = new HashMap<>();
866
867        List<? extends HierarchicalConfiguration<?>> nodes =
868                defConfig.configurationsAt(KEY_CONFIGURATION_LOOKUPS);
869        for (HierarchicalConfiguration<?> config : nodes)
870        {
871            XMLBeanDeclaration decl = new XMLBeanDeclaration(config);
872            String key = config.getString(KEY_LOOKUP_KEY);
873            Lookup lookup = (Lookup) fetchBeanHelper().createBean(decl);
874            lookups.put(key, lookup);
875        }
876
877        if (!lookups.isEmpty())
878        {
879            ConfigurationInterpolator defCI = defConfig.getInterpolator();
880            if (defCI != null)
881            {
882                defCI.registerLookups(lookups);
883            }
884            resultConfig.getInterpolator().registerLookups(lookups);
885        }
886    }
887
888    /**
889     * Creates and initializes a default {@code FileSystem} if the definition
890     * configuration contains a corresponding declaration. The file system
891     * returned by this method is used as default for all file-based child
892     * configuration sources.
893     *
894     * @param config the definition configuration
895     * @return the default {@code FileSystem} (may be <b>null</b>)
896     * @throws ConfigurationException if an error occurs
897     */
898    protected FileSystem initFileSystem(HierarchicalConfiguration<?> config)
899            throws ConfigurationException
900    {
901        if (config.getMaxIndex(FILE_SYSTEM) == 0)
902        {
903            XMLBeanDeclaration decl =
904                    new XMLBeanDeclaration(config, FILE_SYSTEM);
905            return (FileSystem) fetchBeanHelper().createBean(decl);
906        }
907        return null;
908    }
909
910    /**
911     * Handles a file with system properties that may be defined in the
912     * definition configuration. If such property file is configured, all of its
913     * properties are added to the system properties.
914     *
915     * @param config the definition configuration
916     * @param basePath the base path defined for this builder (may be
917     *        <b>null</b>)
918     * @throws ConfigurationException if an error occurs.
919     */
920    protected void initSystemProperties(HierarchicalConfiguration<?> config,
921            String basePath) throws ConfigurationException
922    {
923        String fileName = config.getString(KEY_SYSTEM_PROPS);
924        if (fileName != null)
925        {
926            try
927            {
928                SystemConfiguration.setSystemProperties(basePath, fileName);
929            }
930            catch (Exception ex)
931            {
932                throw new ConfigurationException(
933                        "Error setting system properties from " + fileName, ex);
934            }
935        }
936    }
937
938    /**
939     * Creates and initializes a default {@code EntityResolver} if the
940     * definition configuration contains a corresponding declaration.
941     *
942     * @param config the definition configuration
943     * @param xmlParams the (already partly initialized) object with XML
944     *        parameters; here the new resolver is to be stored
945     * @throws ConfigurationException if an error occurs
946     */
947    protected void configureEntityResolver(HierarchicalConfiguration<?> config,
948            XMLBuilderParametersImpl xmlParams) throws ConfigurationException
949    {
950        if (config.getMaxIndex(KEY_ENTITY_RESOLVER) == 0)
951        {
952            XMLBeanDeclaration decl =
953                    new XMLBeanDeclaration(config, KEY_ENTITY_RESOLVER, true);
954            EntityResolver resolver =
955                    (EntityResolver) fetchBeanHelper().createBean(decl,
956                            CatalogResolver.class);
957            FileSystem fileSystem = xmlParams.getFileHandler().getFileSystem();
958            if (fileSystem != null)
959            {
960                BeanHelper.setProperty(resolver, "fileSystem", fileSystem);
961            }
962            String basePath = xmlParams.getFileHandler().getBasePath();
963            if (basePath != null)
964            {
965                BeanHelper.setProperty(resolver, "baseDir", basePath);
966            }
967            ConfigurationInterpolator ci = new ConfigurationInterpolator();
968            ci.registerLookups(fetchPrefixLookups());
969            BeanHelper.setProperty(resolver, "interpolator", ci);
970
971            xmlParams.setEntityResolver(resolver);
972        }
973    }
974
975    /**
976     * Returns the {@code ConfigurationBuilderProvider} for the given tag. This
977     * method is called during creation of the result configuration. (It is not
978     * allowed to call it at another point of time; result is then
979     * unpredictable!) It supports all default providers and custom providers
980     * added through the parameters object as well.
981     *
982     * @param tagName the name of the tag
983     * @return the provider that was registered for this tag or <b>null</b> if
984     *         there is none
985     */
986    protected ConfigurationBuilderProvider providerForTag(String tagName)
987    {
988        return currentParameters.providerForTag(tagName);
989    }
990
991    /**
992     * Initializes a parameters object for a child builder. This combined
993     * configuration builder has a bunch of properties which may be inherited by
994     * child configurations, e.g. the base path, the file system, etc. While
995     * processing the builders for child configurations, this method is called
996     * for each parameters object for a child builder. It initializes some
997     * properties of the passed in parameters objects which are derived from
998     * this parent builder.
999     *
1000     * @param params the parameters object to be initialized
1001     */
1002    protected void initChildBuilderParameters(BuilderParameters params)
1003    {
1004        initDefaultChildParameters(params);
1005
1006        if (params instanceof BasicBuilderParameters)
1007        {
1008            initChildBasicParameters((BasicBuilderParameters) params);
1009        }
1010        if (params instanceof XMLBuilderProperties<?>)
1011        {
1012            initChildXMLParameters((XMLBuilderProperties<?>) params);
1013        }
1014        if (params instanceof FileBasedBuilderProperties<?>)
1015        {
1016            initChildFileBasedParameters((FileBasedBuilderProperties<?>) params);
1017        }
1018        if (params instanceof CombinedBuilderParametersImpl)
1019        {
1020            initChildCombinedParameters((CombinedBuilderParametersImpl) params);
1021        }
1022    }
1023
1024    /**
1025     * Initializes the event listeners of the specified builder from this
1026     * object. This method is used to inherit all listeners from a parent
1027     * builder.
1028     *
1029     * @param dest the destination builder object which is to be initialized
1030     */
1031    void initChildEventListeners(
1032            BasicConfigurationBuilder<? extends Configuration> dest)
1033    {
1034        copyEventListeners(dest);
1035    }
1036
1037    /**
1038     * Returns the configuration object that is currently constructed. This
1039     * method can be called during construction of the result configuration. It
1040     * is intended for internal usage, e.g. some specialized builder providers
1041     * need access to this configuration to perform advanced initialization.
1042     *
1043     * @return the configuration that us currently under construction
1044     */
1045    CombinedConfiguration getConfigurationUnderConstruction()
1046    {
1047        return currentConfiguration;
1048    }
1049
1050    /**
1051     * Initializes a bean using the current {@code BeanHelper}. This is needed
1052     * by builder providers when the configuration objects for sub builders are
1053     * constructed.
1054     *
1055     * @param bean the bean to be initialized
1056     * @param decl the {@code BeanDeclaration}
1057     */
1058    void initBean(Object bean, BeanDeclaration decl)
1059    {
1060        fetchBeanHelper().initBean(bean, decl);
1061    }
1062
1063    /**
1064     * Initializes the current parameters object. This object has either been
1065     * passed at builder configuration time or it is newly created. In any
1066     * case, it is manipulated during result creation.
1067     */
1068    private void setUpCurrentParameters()
1069    {
1070        currentParameters =
1071                CombinedBuilderParametersImpl.fromParameters(getParameters(), true);
1072        currentParameters.registerMissingProviders(DEFAULT_PROVIDERS_MAP);
1073    }
1074
1075    /**
1076     * Sets up an XML parameters object which is used to store properties
1077     * related to XML and file-based configurations during creation of the
1078     * result configuration. The properties stored in this object can be
1079     * inherited to child configurations.
1080     *
1081     * @throws ConfigurationException if an error occurs
1082     */
1083    private void setUpCurrentXMLParameters() throws ConfigurationException
1084    {
1085        currentXMLParameters = new XMLBuilderParametersImpl();
1086        initDefaultBasePath();
1087    }
1088
1089    /**
1090     * Sets up a parent {@code ConfigurationInterpolator} object. This object
1091     * has a default {@link Lookup} querying the resulting combined
1092     * configuration. Thus interpolation works globally across all configuration
1093     * sources.
1094     *
1095     * @param resultConfig the result configuration
1096     * @param defConfig the definition configuration
1097     */
1098    private void setUpParentInterpolator(Configuration resultConfig,
1099            Configuration defConfig)
1100    {
1101        parentInterpolator = new ConfigurationInterpolator();
1102        parentInterpolator.addDefaultLookup(new ConfigurationLookup(
1103                resultConfig));
1104        ConfigurationInterpolator defInterpolator = defConfig.getInterpolator();
1105        if (defInterpolator != null)
1106        {
1107            defInterpolator.setParentInterpolator(parentInterpolator);
1108        }
1109    }
1110
1111    /**
1112     * Initializes the default base path for all file-based child configuration
1113     * sources. The base path can be explicitly defined in the parameters of
1114     * this builder. Otherwise, if the definition builder is a file-based
1115     * builder, it is obtained from there.
1116     *
1117     * @throws ConfigurationException if an error occurs
1118     */
1119    private void initDefaultBasePath() throws ConfigurationException
1120    {
1121        assert currentParameters != null : "Current parameters undefined!";
1122        if (currentParameters.getBasePath() != null)
1123        {
1124            currentXMLParameters.setBasePath(currentParameters.getBasePath());
1125        }
1126        else
1127        {
1128            ConfigurationBuilder<? extends HierarchicalConfiguration<?>> defBuilder =
1129                    getDefinitionBuilder();
1130            if (defBuilder instanceof FileBasedConfigurationBuilder)
1131            {
1132                @SuppressWarnings("rawtypes")
1133                FileBasedConfigurationBuilder fileBuilder =
1134                        (FileBasedConfigurationBuilder) defBuilder;
1135                URL url = fileBuilder.getFileHandler().getURL();
1136                currentXMLParameters.setBasePath((url != null) ? url
1137                        .toExternalForm() : fileBuilder.getFileHandler()
1138                        .getBasePath());
1139            }
1140        }
1141    }
1142
1143    /**
1144     * Executes the {@link org.apache.commons.configuration2.builder.DefaultParametersManager
1145     * DefaultParametersManager} stored in the current
1146     * parameters on the passed in parameters object. If default handlers have been
1147     * registered for this type of parameters, an initialization is now
1148     * performed. This method is called before the parameters object is
1149     * initialized from the configuration definition file. So default values
1150     * can be overridden later with concrete property definitions.
1151     *
1152     * @param params the parameters to be initialized
1153     * @throws org.apache.commons.configuration2.ex.ConfigurationRuntimeException if an error
1154     *         occurs when copying properties
1155     */
1156    private void initDefaultChildParameters(BuilderParameters params)
1157    {
1158        currentParameters.getChildDefaultParametersManager()
1159                .initializeParameters(params);
1160    }
1161
1162    /**
1163     * Initializes basic builder parameters for a child configuration with
1164     * default settings set for this builder. This implementation ensures that
1165     * all {@code Lookup} objects are propagated to child configurations and
1166     * interpolation is setup correctly.
1167     *
1168     * @param params the parameters object
1169     */
1170    private void initChildBasicParameters(BasicBuilderParameters params)
1171    {
1172        params.setPrefixLookups(fetchPrefixLookups());
1173        params.setParentInterpolator(parentInterpolator);
1174        if (currentParameters.isInheritSettings())
1175        {
1176            params.inheritFrom(getParameters());
1177        }
1178    }
1179
1180    /**
1181     * Initializes a parameters object for a file-based configuration with
1182     * properties already set for this parent builder. This method handles
1183     * properties like a default file system or a base path.
1184     *
1185     * @param params the parameters object
1186     */
1187    private void initChildFileBasedParameters(
1188            FileBasedBuilderProperties<?> params)
1189    {
1190        params.setBasePath(getBasePath());
1191        params.setFileSystem(currentXMLParameters.getFileHandler()
1192                .getFileSystem());
1193    }
1194
1195    /**
1196     * Initializes a parameters object for an XML configuration with properties
1197     * already set for this parent builder.
1198     *
1199     * @param params the parameters object
1200     */
1201    private void initChildXMLParameters(XMLBuilderProperties<?> params)
1202    {
1203        params.setEntityResolver(currentXMLParameters.getEntityResolver());
1204    }
1205
1206    /**
1207     * Initializes a parameters object for a combined configuration builder with
1208     * properties already set for this parent builder. This implementation deals
1209     * only with a subset of properties. Other properties are already handled by
1210     * the specialized builder provider.
1211     *
1212     * @param params the parameters object
1213     */
1214    private void initChildCombinedParameters(
1215            CombinedBuilderParametersImpl params)
1216    {
1217        params.registerMissingProviders(currentParameters);
1218        params.setBasePath(getBasePath());
1219    }
1220
1221    /**
1222     * Obtains the data object for the configuration sources and the
1223     * corresponding builders. This object is created on first access and reset
1224     * when the definition builder sends a change event. This method is called
1225     * in a synchronized block.
1226     *
1227     * @return the object with information about configuration sources
1228     * @throws ConfigurationException if an error occurs
1229     */
1230    private ConfigurationSourceData getSourceData()
1231            throws ConfigurationException
1232    {
1233        if (sourceData == null)
1234        {
1235            if (currentParameters == null)
1236            {
1237                setUpCurrentParameters();
1238                setUpCurrentXMLParameters();
1239            }
1240            sourceData = createSourceData();
1241        }
1242        return sourceData;
1243    }
1244
1245    /**
1246     * Creates the data object for configuration sources and the corresponding
1247     * builders.
1248     *
1249     * @return the newly created data object
1250     * @throws ConfigurationException if an error occurs
1251     */
1252    private ConfigurationSourceData createSourceData()
1253            throws ConfigurationException
1254    {
1255        ConfigurationSourceData result = new ConfigurationSourceData();
1256        result.initFromDefinitionConfiguration(getDefinitionConfiguration());
1257        return result;
1258    }
1259
1260    /**
1261     * Returns the current base path of this configuration builder. This is used
1262     * for instance by all file-based child configurations.
1263     *
1264     * @return the base path
1265     */
1266    private String getBasePath()
1267    {
1268        return currentXMLParameters.getFileHandler().getBasePath();
1269    }
1270
1271    /**
1272     * Registers providers defined in the configuration.
1273     *
1274     * @param defConfig the definition configuration
1275     * @throws ConfigurationException if an error occurs
1276     */
1277    private void registerConfiguredProviders(HierarchicalConfiguration<?> defConfig)
1278            throws ConfigurationException
1279    {
1280        List<? extends HierarchicalConfiguration<?>> nodes =
1281                defConfig.configurationsAt(KEY_CONFIGURATION_PROVIDERS);
1282        for (HierarchicalConfiguration<?> config : nodes)
1283        {
1284            XMLBeanDeclaration decl = new XMLBeanDeclaration(config);
1285            String key = config.getString(KEY_PROVIDER_KEY);
1286            currentParameters.registerProvider(key,
1287                    (ConfigurationBuilderProvider) fetchBeanHelper().createBean(decl));
1288        }
1289    }
1290
1291    /**
1292     * Adds a listener at the given definition builder which resets this builder
1293     * when a reset of the definition builder happens. This way it is ensured
1294     * that this builder produces a new combined configuration when its
1295     * definition configuration changes.
1296     *
1297     * @param defBuilder the definition builder
1298     */
1299    private void addDefinitionBuilderChangeListener(
1300            final ConfigurationBuilder<? extends HierarchicalConfiguration<?>> defBuilder)
1301    {
1302        defBuilder.addEventListener(ConfigurationBuilderEvent.RESET,
1303                new EventListener<ConfigurationBuilderEvent>()
1304                {
1305            @Override
1306            public void onEvent(ConfigurationBuilderEvent event)
1307            {
1308                synchronized (CombinedConfigurationBuilder.this)
1309                {
1310                    reset();
1311                    definitionBuilder = defBuilder;
1312                }
1313            }
1314        });
1315    }
1316
1317    /**
1318     * Returns a map with the current prefix lookup objects. This map is
1319     * obtained from the {@code ConfigurationInterpolator} of the configuration
1320     * under construction.
1321     *
1322     * @return the map with current prefix lookups (may be <b>null</b>)
1323     */
1324    private Map<String, ? extends Lookup> fetchPrefixLookups()
1325    {
1326        CombinedConfiguration cc = getConfigurationUnderConstruction();
1327        return (cc != null) ? cc.getInterpolator().getLookups() : null;
1328    }
1329
1330    /**
1331     * Creates {@code ConfigurationDeclaration} objects for the specified
1332     * configurations.
1333     *
1334     * @param configs the list with configurations
1335     * @return a collection with corresponding declarations
1336     */
1337    private Collection<ConfigurationDeclaration> createDeclarations(
1338            Collection<? extends HierarchicalConfiguration<?>> configs)
1339    {
1340        Collection<ConfigurationDeclaration> declarations =
1341                new ArrayList<>(configs.size());
1342        for (HierarchicalConfiguration<?> c : configs)
1343        {
1344            declarations.add(new ConfigurationDeclaration(this, c));
1345        }
1346        return declarations;
1347    }
1348
1349    /**
1350     * Initializes the list nodes of the node combiner for the given combined
1351     * configuration. This information can be set in the header section of the
1352     * configuration definition file for both the override and the union
1353     * combiners.
1354     *
1355     * @param cc the combined configuration to initialize
1356     * @param defConfig the definition configuration
1357     * @param key the key for the list nodes
1358     */
1359    private static void initNodeCombinerListNodes(CombinedConfiguration cc,
1360            HierarchicalConfiguration<?> defConfig, String key)
1361    {
1362        List<Object> listNodes = defConfig.getList(key);
1363        for (Object listNode : listNodes)
1364        {
1365            cc.getNodeCombiner().addListNode((String) listNode);
1366        }
1367    }
1368
1369    /**
1370     * Creates the map with the default configuration builder providers.
1371     *
1372     * @return the map with default providers
1373     */
1374    private static Map<String, ConfigurationBuilderProvider> createDefaultProviders()
1375    {
1376        Map<String, ConfigurationBuilderProvider> providers =
1377                new HashMap<>();
1378        for (int i = 0; i < DEFAULT_TAGS.length; i++)
1379        {
1380            providers.put(DEFAULT_TAGS[i], DEFAULT_PROVIDERS[i]);
1381        }
1382        return providers;
1383    }
1384
1385    static
1386    {
1387        DEFAULT_PROVIDERS_MAP = createDefaultProviders();
1388    }
1389
1390    /**
1391     * A data class for storing information about all configuration sources
1392     * defined for a combined builder.
1393     */
1394    private class ConfigurationSourceData
1395    {
1396        /** A list with data for all builders for override configurations. */
1397        private final List<ConfigurationDeclaration> overrideDeclarations;
1398
1399        /** A list with data for all builders for union configurations. */
1400        private final List<ConfigurationDeclaration> unionDeclarations;
1401
1402        /** A list with the builders for override configurations. */
1403        private final List<ConfigurationBuilder<? extends Configuration>> overrideBuilders;
1404
1405        /** A list with the builders for union configurations. */
1406        private final List<ConfigurationBuilder<? extends Configuration>> unionBuilders;
1407
1408        /** A map for direct access to a builder by its name. */
1409        private final Map<String, ConfigurationBuilder<? extends Configuration>> namedBuilders;
1410
1411        /** A collection with all child builders. */
1412        private final Collection<ConfigurationBuilder<? extends Configuration>> allBuilders;
1413
1414        /** A listener for reacting on changes of sub builders. */
1415        private final EventListener<ConfigurationBuilderEvent> changeListener;
1416
1417        /**
1418         * Creates a new instance of {@code ConfigurationSourceData}.
1419         */
1420        public ConfigurationSourceData()
1421        {
1422            overrideDeclarations = new ArrayList<>();
1423            unionDeclarations = new ArrayList<>();
1424            overrideBuilders = new ArrayList<>();
1425            unionBuilders = new ArrayList<>();
1426            namedBuilders = new HashMap<>();
1427            allBuilders = new LinkedList<>();
1428            changeListener = createBuilderChangeListener();
1429        }
1430
1431        /**
1432         * Initializes this object from the specified definition configuration.
1433         *
1434         * @param config the definition configuration
1435         * @throws ConfigurationException if an error occurs
1436         */
1437        public void initFromDefinitionConfiguration(
1438                HierarchicalConfiguration<?> config) throws ConfigurationException
1439        {
1440            overrideDeclarations.addAll(createDeclarations(fetchTopLevelOverrideConfigs(config)));
1441            overrideDeclarations.addAll(createDeclarations(config.childConfigurationsAt(KEY_OVERRIDE)));
1442            unionDeclarations.addAll(createDeclarations(config.childConfigurationsAt(KEY_UNION)));
1443        }
1444
1445        /**
1446         * Processes the declaration of configuration builder providers, creates
1447         * the corresponding builder if necessary, obtains configurations, and
1448         * adds them to the specified result configuration.
1449         *
1450         * @param ccResult the result configuration
1451         * @param srcDecl the collection with the declarations of configuration
1452         *        sources to process
1453         * @return a list with configuration builders
1454         * @throws ConfigurationException if an error occurs
1455         */
1456        public List<ConfigurationBuilder<? extends Configuration>> createAndAddConfigurations(
1457                CombinedConfiguration ccResult,
1458                List<ConfigurationDeclaration> srcDecl,
1459                List<ConfigurationBuilder<? extends Configuration>> builders)
1460                throws ConfigurationException
1461        {
1462            boolean createBuilders = builders.isEmpty();
1463            List<ConfigurationBuilder<? extends Configuration>> newBuilders;
1464            if (createBuilders)
1465            {
1466                newBuilders = new ArrayList<>(srcDecl.size());
1467            }
1468            else
1469            {
1470                newBuilders = builders;
1471            }
1472
1473            for (int i = 0; i < srcDecl.size(); i++)
1474            {
1475                ConfigurationBuilder<? extends Configuration> b;
1476                if (createBuilders)
1477                {
1478                    b = createConfigurationBuilder(srcDecl.get(i));
1479                    newBuilders.add(b);
1480                }
1481                else
1482                {
1483                    b = builders.get(i);
1484                }
1485                addChildConfiguration(ccResult, srcDecl.get(i), b);
1486            }
1487
1488            return newBuilders;
1489        }
1490
1491        /**
1492         * Frees resources used by this object and performs clean up. This
1493         * method is called when the owning builder is reset.
1494         */
1495        public void cleanUp()
1496        {
1497            for (ConfigurationBuilder<?> b : getChildBuilders())
1498            {
1499                b.removeEventListener(ConfigurationBuilderEvent.RESET,
1500                        changeListener);
1501            }
1502            namedBuilders.clear();
1503        }
1504
1505        /**
1506         * Returns a collection containing the builders for all child
1507         * configuration sources.
1508         *
1509         * @return the child configuration builders
1510         */
1511        public Collection<ConfigurationBuilder<? extends Configuration>> getChildBuilders()
1512        {
1513            return allBuilders;
1514        }
1515
1516        /**
1517         * Returns a collection with all configuration source declarations
1518         * defined in the override section.
1519         *
1520         * @return the override configuration builders
1521         */
1522        public List<ConfigurationDeclaration> getOverrideSources()
1523        {
1524            return overrideDeclarations;
1525        }
1526
1527        /**
1528         * Returns a collection with all configuration source declarations
1529         * defined in the union section.
1530         *
1531         * @return the union configuration builders
1532         */
1533        public List<ConfigurationDeclaration> getUnionSources()
1534        {
1535            return unionDeclarations;
1536        }
1537
1538        /**
1539         * Returns the {@code ConfigurationBuilder} with the given name. If no
1540         * such builder is defined in the definition configuration, result is
1541         * <b>null</b>.
1542         *
1543         * @param name the name of the builder in question
1544         * @return the builder with this name or <b>null</b>
1545         */
1546        public ConfigurationBuilder<? extends Configuration> getNamedBuilder(
1547                String name)
1548        {
1549            return namedBuilders.get(name);
1550        }
1551
1552        /**
1553         * Returns a set with the names of all known named builders.
1554         *
1555         * @return the names of the available sub builders
1556         */
1557        public Set<String> builderNames()
1558        {
1559            return namedBuilders.keySet();
1560        }
1561
1562        /**
1563         * Creates a configuration builder based on a source declaration in the
1564         * definition configuration.
1565         *
1566         * @param decl the current {@code ConfigurationDeclaration}
1567         * @return the newly created builder
1568         * @throws ConfigurationException if an error occurs
1569         */
1570        private ConfigurationBuilder<? extends Configuration> createConfigurationBuilder(
1571                ConfigurationDeclaration decl) throws ConfigurationException
1572        {
1573            ConfigurationBuilderProvider provider =
1574                    providerForTag(decl.getConfiguration().getRootElementName());
1575            if (provider == null)
1576            {
1577                throw new ConfigurationException(
1578                        "Unsupported configuration source: "
1579                                + decl.getConfiguration().getRootElementName());
1580            }
1581
1582            ConfigurationBuilder<? extends Configuration> builder =
1583                    provider.getConfigurationBuilder(decl);
1584            if (decl.getName() != null)
1585            {
1586                namedBuilders.put(decl.getName(), builder);
1587            }
1588            allBuilders.add(builder);
1589            builder.addEventListener(ConfigurationBuilderEvent.RESET,
1590                    changeListener);
1591            return builder;
1592        }
1593
1594        /**
1595         * Creates a new configuration using the specified builder and adds it
1596         * to the resulting combined configuration.
1597         *
1598         * @param ccResult the resulting combined configuration
1599         * @param decl the current {@code ConfigurationDeclaration}
1600         * @param builder the configuration builder
1601         * @throws ConfigurationException if an error occurs
1602         */
1603        private void addChildConfiguration(CombinedConfiguration ccResult,
1604                ConfigurationDeclaration decl,
1605                ConfigurationBuilder<? extends Configuration> builder)
1606                throws ConfigurationException
1607        {
1608            try
1609            {
1610                ccResult.addConfiguration(
1611                        builder.getConfiguration(),
1612                        decl.getName(), decl.getAt());
1613            }
1614            catch (ConfigurationException cex)
1615            {
1616                // ignore exceptions for optional configurations
1617                if (!decl.isOptional())
1618                {
1619                    throw cex;
1620                }
1621            }
1622        }
1623
1624        /**
1625         * Creates a listener for builder change events. This listener is
1626         * registered at all builders for child configurations.
1627         */
1628        private EventListener<ConfigurationBuilderEvent> createBuilderChangeListener()
1629        {
1630            return new EventListener<ConfigurationBuilderEvent>()
1631            {
1632                @Override
1633                public void onEvent(ConfigurationBuilderEvent event)
1634                {
1635                    resetResult();
1636                }
1637            };
1638        }
1639
1640        /**
1641         * Finds the override configurations that are defined as top level
1642         * elements in the configuration definition file. This method fetches
1643         * the child elements of the root node and removes the nodes that
1644         * represent other configuration sections. The remaining nodes are
1645         * treated as definitions for override configurations.
1646         *
1647         * @param config the definition configuration
1648         * @return a list with sub configurations for the top level override
1649         *         configurations
1650         */
1651        private List<? extends HierarchicalConfiguration<?>> fetchTopLevelOverrideConfigs(
1652                HierarchicalConfiguration<?> config)
1653        {
1654
1655            List<? extends HierarchicalConfiguration<?>> configs =
1656                    config.childConfigurationsAt(null);
1657            for (Iterator<? extends HierarchicalConfiguration<?>> it =
1658                    configs.iterator(); it.hasNext();)
1659            {
1660                String nodeName = it.next().getRootElementName();
1661                for (String element : CONFIG_SECTIONS)
1662                {
1663                    if (element.equals(nodeName))
1664                    {
1665                        it.remove();
1666                        break;
1667                    }
1668                }
1669            }
1670            return configs;
1671        }
1672    }
1673}