src/main/java/org/apache/commons/configuration2/builder/BasicBuilderParameters.java - commons-configuration - Git at Google

 /*
  * Licensed to the Apache Software Foundation (ASF) under one or more
  * contributor license agreements.  See the NOTICE file distributed with
  * this work for additional information regarding copyright ownership.
  * The ASF licenses this file to You under the Apache License, Version 2.0
  * (the "License"); you may not use this file except in compliance with
  * the License.  You may obtain a copy of the License at
  *
  *     https://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package org.apache.commons.configuration2.builder;

 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.Map;

 import org.apache.commons.configuration2.ConfigurationDecoder;
 import org.apache.commons.configuration2.beanutils.BeanHelper;
 import org.apache.commons.configuration2.convert.ConversionHandler;
 import org.apache.commons.configuration2.convert.ListDelimiterHandler;
 import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
 import org.apache.commons.configuration2.interpol.InterpolatorSpecification;
 import org.apache.commons.configuration2.interpol.Lookup;
 import org.apache.commons.configuration2.io.ConfigurationLogger;
 import org.apache.commons.configuration2.sync.Synchronizer;

 /**
  * <p>
  * An implementation of {@code BuilderParameters} which handles the parameters of a {@link ConfigurationBuilder} common
  * to all concrete {@code Configuration} implementations.
  * </p>
  * <p>
  * This class provides methods for setting standard properties supported by the {@code AbstractConfiguration} base
  * class. A fluent interface can be used to set property values.
  * </p>
  * <p>
  * This class is not thread-safe. It is intended that an instance is constructed and initialized by a single thread
  * during configuration of a {@code ConfigurationBuilder}.
  * </p>
  *
  * @since 2.0
  */
 public class BasicBuilderParameters implements Cloneable, BuilderParameters, BasicBuilderProperties<BasicBuilderParameters> {

     /** The key of the <em>throwExceptionOnMissing</em> property. */
     private static final String PROP_THROW_EXCEPTION_ON_MISSING = "throwExceptionOnMissing";

     /** The key of the <em>listDelimiterHandler</em> property. */
     private static final String PROP_LIST_DELIMITER_HANDLER = "listDelimiterHandler";

     /** The key of the <em>logger</em> property. */
     private static final String PROP_LOGGER = "logger";

     /** The key for the <em>interpolator</em> property. */
     private static final String PROP_INTERPOLATOR = "interpolator";

     /** The key for the <em>prefixLookups</em> property. */
     private static final String PROP_PREFIX_LOOKUPS = "prefixLookups";

     /** The key for the <em>defaultLookups</em> property. */
     private static final String PROP_DEFAULT_LOOKUPS = "defaultLookups";

     /** The key for the <em>parentInterpolator</em> property. */
     private static final String PROP_PARENT_INTERPOLATOR = "parentInterpolator";

     /** The key for the <em>synchronizer</em> property. */
     private static final String PROP_SYNCHRONIZER = "synchronizer";

     /** The key for the <em>conversionHandler</em> property. */
     private static final String PROP_CONVERSION_HANDLER = "conversionHandler";

     /** The key for the <em>configurationDecoder</em> property. */
     private static final String PROP_CONFIGURATION_DECODER = "configurationDecoder";

     /** The key for the {@code BeanHelper}. */
     private static final String PROP_BEAN_HELPER = RESERVED_PARAMETER_PREFIX + "BeanHelper";

     /**
      * Checks whether a map with parameters is present. Throws an exception if not.
      *
      * @param params the map with parameters to check
      * @throws IllegalArgumentException if the map is <strong>null</strong>
      */
     private static void checkParameters(final Map<String, Object> params) {
         if (params == null) {
             throw new IllegalArgumentException("Parameters map must not be null!");
         }
     }

     /**
      * Creates defensive copies for collection structures when constructing the map with parameters. It should not be
      * possible to modify this object's internal state when having access to the parameters map.
      *
      * @param params the map with parameters to be passed to the caller
      */
     private static void createDefensiveCopies(final HashMap<String, Object> params) {
         final Map<String, ? extends Lookup> prefixLookups = fetchPrefixLookups(params);
         if (prefixLookups != null) {
             params.put(PROP_PREFIX_LOOKUPS, new HashMap<>(prefixLookups));
         }
         final Collection<? extends Lookup> defLookups = fetchDefaultLookups(params);
         if (defLookups != null) {
             params.put(PROP_DEFAULT_LOOKUPS, new ArrayList<>(defLookups));
         }
     }

     /**
      * Tests whether the passed in map with parameters contains a valid collection with default lookups. This method works
      * like {@link #fetchAndCheckPrefixLookups(Map)}, but tests the default lookups collection.
      *
      * @param params the map with parameters
      * @return the collection with default lookups (may be <strong>null</strong>)
      * @throws IllegalArgumentException if invalid data is found
      */
     private static Collection<? extends Lookup> fetchAndCheckDefaultLookups(final Map<String, Object> params) {
         final Collection<?> col = fetchParameter(params, PROP_DEFAULT_LOOKUPS, Collection.class);
         if (col == null) {
             return null;
         }

         if (col.stream().noneMatch(Lookup.class::isInstance)) {
             throw new IllegalArgumentException("Collection with default lookups contains invalid data: " + col);
         }
         return fetchDefaultLookups(params);
     }

     /**
      * Tests whether the passed in map with parameters contains a map with prefix lookups. This method is used if the
      * parameters map is from an insecure source and we cannot be sure that it contains valid data. Therefore, we have to
      * map that the key for the prefix lookups actually points to a map containing keys and values of expected data types.
      *
      * @param params the parameters map
      * @return the obtained map with prefix lookups
      * @throws IllegalArgumentException if the map contains invalid data
      */
     private static Map<String, ? extends Lookup> fetchAndCheckPrefixLookups(final Map<String, Object> params) {
         final Map<?, ?> prefixes = fetchParameter(params, PROP_PREFIX_LOOKUPS, Map.class);
         if (prefixes == null) {
             return null;
         }
         prefixes.forEach((k, v) -> {
             if (!(k instanceof String) || !(v instanceof Lookup)) {
                 throw new IllegalArgumentException("Map with prefix lookups contains invalid data: " + prefixes);
             }
         });
         return fetchPrefixLookups(params);
     }

     /**
      * Obtains the {@code BeanHelper} object from the specified map with parameters. This method can be used to obtain an
      * instance from a parameters map that has been set via the {@code setBeanHelper()} method. If no such instance is
      * found, result is <strong>null</strong>.
      *
      * @param params the map with parameters (must not be <strong>null</strong>)
      * @return the {@code BeanHelper} stored in this map or <strong>null</strong>
      * @throws IllegalArgumentException if the map is <strong>null</strong>
      */
     public static BeanHelper fetchBeanHelper(final Map<String, Object> params) {
         checkParameters(params);
         return (BeanHelper) params.get(PROP_BEAN_HELPER);
     }

     /**
      * Obtains the collection with default lookups from the parameters map.
      *
      * @param params the map with parameters
      * @return the collection with default lookups (may be <strong>null</strong>)
      */
     private static Collection<? extends Lookup> fetchDefaultLookups(final Map<String, Object> params) {
         // This is safe to cast because we either have full control over the map
         // and thus know the types of the contained values or have checked
         // the content before
         @SuppressWarnings("unchecked")
         final Collection<? extends Lookup> defLookups = (Collection<? extends Lookup>) params.get(PROP_DEFAULT_LOOKUPS);
         return defLookups;
     }

     /**
      * Obtains a specification for a {@link ConfigurationInterpolator} from the specified map with parameters. All
      * properties related to interpolation are evaluated and added to the specification object.
      *
      * @param params the map with parameters (must not be <strong>null</strong>)
      * @return an {@code InterpolatorSpecification} object constructed with data from the map
      * @throws IllegalArgumentException if the map is <strong>null</strong> or contains invalid data
      */
     public static InterpolatorSpecification fetchInterpolatorSpecification(final Map<String, Object> params) {
         checkParameters(params);
         return new InterpolatorSpecification.Builder().withInterpolator(fetchParameter(params, PROP_INTERPOLATOR, ConfigurationInterpolator.class))
             .withParentInterpolator(fetchParameter(params, PROP_PARENT_INTERPOLATOR, ConfigurationInterpolator.class))
             .withPrefixLookups(fetchAndCheckPrefixLookups(params)).withDefaultLookups(fetchAndCheckDefaultLookups(params)).create();
     }

     /**
      * Obtains a parameter from a map and performs a type check.
      *
      * @param params the map with parameters
      * @param key the key of the parameter
      * @param expClass the expected class of the parameter value
      * @param <T> the parameter type
      * @return the value of the parameter in the correct data type
      * @throws IllegalArgumentException if the parameter is not of the expected type
      */
     private static <T> T fetchParameter(final Map<String, Object> params, final String key, final Class<T> expClass) {
         final Object value = params.get(key);
         if (value == null) {
             return null;
         }
         if (!expClass.isInstance(value)) {
             throw new IllegalArgumentException(String.format("Parameter %s is not of type %s!", key, expClass.getSimpleName()));
         }
         return expClass.cast(value);
     }

     /**
      * Obtains the map with prefix lookups from the parameters map.
      *
      * @param params the map with parameters
      * @return the map with prefix lookups (may be <strong>null</strong>)
      */
     private static Map<String, ? extends Lookup> fetchPrefixLookups(final Map<String, Object> params) {
         // This is safe to cast because we either have full control over the map
         // and thus know the types of the contained values or have checked
         // the content before
         @SuppressWarnings("unchecked")
         final Map<String, ? extends Lookup> prefixLookups = (Map<String, ? extends Lookup>) params.get(PROP_PREFIX_LOOKUPS);
         return prefixLookups;
     }

     /** The map for storing the current property values. */
     private Map<String, Object> properties;

     /**
      * Creates a new instance of {@code BasicBuilderParameters}.
      */
     public BasicBuilderParameters() {
         properties = new HashMap<>();
     }

     /**
      * Clones this object. This is useful because multiple builder instances may use a similar set of parameters. However,
      * single instances of parameter objects must not assigned to multiple builders. Therefore, cloning a parameters object
      * provides a solution for this use case. This method creates a new parameters object with the same content as this one.
      * The internal map storing the parameter values is cloned, too, also collection structures contained in this map.
      * However, no a full deep clone operation is performed. Objects like a {@code ConfigurationInterpolator} or
      * {@code Lookup}s are shared between this and the newly created instance.
      *
      * @return a clone of this object
      */
     @Override
     public BasicBuilderParameters clone() {
         try {
             final BasicBuilderParameters copy = (BasicBuilderParameters) super.clone();
             copy.properties = getParameters();
             return copy;
         } catch (final CloneNotSupportedException cnex) {
             // should not happen
             throw new AssertionError(cnex);
         }
     }

     /**
      * Copies a number of properties from the given map into this object. Properties are only copied if they are defined in
      * the source map.
      *
      * @param source the source map
      * @param keys the keys to be copied
      */
     protected void copyPropertiesFrom(final Map<String, ?> source, final String... keys) {
         for (final String key : keys) {
             final Object value = source.get(key);
             if (value != null) {
                 storeProperty(key, value);
             }
         }
     }

     /**
      * Obtains the value of the specified property from the internal map. This method can be used by derived classes if a
      * specific property is to be accessed. If the given key is not found, result is <strong>null</strong>.
      *
      * @param key the key of the property in question
      * @return the value of the property with this key or <strong>null</strong>
      */
     protected Object fetchProperty(final String key) {
         return properties.get(key);
     }

     /**
      * {@inheritDoc} This implementation returns a copy of the internal parameters map with the values set so far.
      * Collection structures (for example for lookup objects) are stored as defensive copies, so the original data cannot be
      * modified.
      */
     @Override
     public Map<String, Object> getParameters() {
         final HashMap<String, Object> result = new HashMap<>(properties);
         if (result.containsKey(PROP_INTERPOLATOR)) {
             // A custom ConfigurationInterpolator overrides lookups
             result.remove(PROP_PREFIX_LOOKUPS);
             result.remove(PROP_DEFAULT_LOOKUPS);
             result.remove(PROP_PARENT_INTERPOLATOR);
         }

         createDefensiveCopies(result);
         return result;
     }

     /**
      * Inherits properties from the specified map. This can be used for instance to reuse parameters from one builder in
      * another builder - also in parent-child relations in which a parent builder creates child builders. The purpose of
      * this method is to let a concrete implementation decide which properties can be inherited. Because parameters are
      * basically organized as a map it would be possible to simply copy over all properties from the source object. However,
      * this is not appropriate in all cases. For instance, some properties - like a {@code ConfigurationInterpolator} - are
      * tightly connected to a configuration and cannot be reused in a different context. For other properties, for example a file
      * name, it does not make sense to copy it. Therefore, an implementation has to be explicit in the properties it wants
      * to take over.
      *
      * @param source the source properties to inherit from
      * @throws IllegalArgumentException if the source map is <strong>null</strong>
      */
     public void inheritFrom(final Map<String, ?> source) {
         if (source == null) {
             throw new IllegalArgumentException("Source properties must not be null!");
         }
         copyPropertiesFrom(source, PROP_BEAN_HELPER, PROP_CONFIGURATION_DECODER, PROP_CONVERSION_HANDLER, PROP_LIST_DELIMITER_HANDLER, PROP_LOGGER,
             PROP_SYNCHRONIZER, PROP_THROW_EXCEPTION_ON_MISSING);
     }

     /**
      * Merges this object with the given parameters object. This method adds all property values defined by the passed in
      * parameters object to the internal storage which are not already in. So properties already defined in this object take
      * precedence. Property names starting with the reserved parameter prefix are ignored.
      *
      * @param p the object whose properties should be merged (must not be <strong>null</strong>)
      * @throws IllegalArgumentException if the passed in object is <strong>null</strong>
      */
     public void merge(final BuilderParameters p) {
         if (p == null) {
             throw new IllegalArgumentException("Parameters to merge must not be null!");
         }
         p.getParameters().forEach((k, v) -> {
             if (!properties.containsKey(k) && !k.startsWith(RESERVED_PARAMETER_PREFIX)) {
                 storeProperty(k, v);
             }
         });
     }

     /**
      * {@inheritDoc} This implementation stores the passed in {@code BeanHelper} object in the internal parameters map, but
      * uses a reserved key, so that it is not used for the initialization of properties of the managed configuration object.
      * The {@code fetchBeanHelper()} method can be used to obtain the {@code BeanHelper} instance from a parameters map.
      */
     @Override
     public BasicBuilderParameters setBeanHelper(final BeanHelper beanHelper) {
         return setProperty(PROP_BEAN_HELPER, beanHelper);
     }

     /**
      * {@inheritDoc} This implementation stores the passed in {@code ConfigurationDecoder} object in the internal parameters
      * map.
      */
     @Override
     public BasicBuilderParameters setConfigurationDecoder(final ConfigurationDecoder decoder) {
         return setProperty(PROP_CONFIGURATION_DECODER, decoder);
     }

     /**
      * {@inheritDoc} This implementation stores the passed in {@code ConversionHandler} object in the internal parameters
      * map.
      */
     @Override
     public BasicBuilderParameters setConversionHandler(final ConversionHandler handler) {
         return setProperty(PROP_CONVERSION_HANDLER, handler);
     }

     /**
      * {@inheritDoc} A defensive copy of the passed in collection is created. A <strong>null</strong> argument causes all default
      * lookups to be removed from the internal parameters map.
      */
     @Override
     public BasicBuilderParameters setDefaultLookups(final Collection<? extends Lookup> lookups) {
         if (lookups == null) {
             properties.remove(PROP_DEFAULT_LOOKUPS);
             return this;
         }
         return setProperty(PROP_DEFAULT_LOOKUPS, new ArrayList<>(lookups));
     }

     /**
      * {@inheritDoc} The passed in {@code ConfigurationInterpolator} is set without modifications.
      */
     @Override
     public BasicBuilderParameters setInterpolator(final ConfigurationInterpolator ci) {
         return setProperty(PROP_INTERPOLATOR, ci);
     }

     /**
      * Sets the value of the <em>listDelimiterHandler</em> property. This property defines the object responsible for
      * dealing with list delimiter and escaping characters. Note:
      * {@link org.apache.commons.configuration2.AbstractConfiguration AbstractConfiguration} does not allow setting this
      * property to <strong>null</strong>. If the default {@code ListDelimiterHandler} is to be used, do not call this method.
      *
      * @param handler the {@code ListDelimiterHandler}
      * @return a reference to this object for method chaining
      */
     @Override
     public BasicBuilderParameters setListDelimiterHandler(final ListDelimiterHandler handler) {
         return setProperty(PROP_LIST_DELIMITER_HANDLER, handler);
     }

     /**
      * Sets the <em>logger</em> property. With this property a concrete {@code Log} object can be set for the configuration.
      * Thus logging behavior can be controlled.
      *
      * @param log the {@code Log} for the configuration produced by this builder
      * @return a reference to this object for method chaining
      */
     @Override
     public BasicBuilderParameters setLogger(final ConfigurationLogger log) {
         return setProperty(PROP_LOGGER, log);
     }

     /**
      * {@inheritDoc} This implementation stores the passed in {@code ConfigurationInterpolator} object in the internal
      * parameters map.
      */
     @Override
     public BasicBuilderParameters setParentInterpolator(final ConfigurationInterpolator parent) {
         return setProperty(PROP_PARENT_INTERPOLATOR, parent);
     }

     /**
      * {@inheritDoc} A defensive copy of the passed in map is created. A <strong>null</strong> argument causes all prefix lookups to
      * be removed from the internal parameters map.
      */
     @Override
     public BasicBuilderParameters setPrefixLookups(final Map<String, ? extends Lookup> lookups) {
         if (lookups == null) {
             properties.remove(PROP_PREFIX_LOOKUPS);
             return this;
         }
         return setProperty(PROP_PREFIX_LOOKUPS, new HashMap<>(lookups));
     }

     /**
      * Helper method for setting a property value.
      *
      * @param key the key of the property
      * @param value the value of the property
      * @return a reference to this object
      */
     private BasicBuilderParameters setProperty(final String key, final Object value) {
         storeProperty(key, value);
         return this;
     }

     /**
      * {@inheritDoc} This implementation stores the passed in {@code Synchronizer} object in the internal parameters map.
      */
     @Override
     public BasicBuilderParameters setSynchronizer(final Synchronizer sync) {
         return setProperty(PROP_SYNCHRONIZER, sync);
     }

     /**
      * Sets the value of the <em>throwExceptionOnMissing</em> property. This property controls the configuration's behavior
      * if missing properties are queried: a value of <strong>true</strong> causes the configuration to throw an exception, for a value
      * of <strong>false</strong> it will return <strong>null</strong> values. (Note: Methods returning a primitive data type will always throw
      * an exception if the property is not defined.)
      *
      * @param b the value of the property
      * @return a reference to this object for method chaining
      */
     @Override
     public BasicBuilderParameters setThrowExceptionOnMissing(final boolean b) {
         return setProperty(PROP_THROW_EXCEPTION_ON_MISSING, Boolean.valueOf(b));
     }

     /**
      * Sets a property for this parameters object. Properties are stored in an internal map. With this method a new entry
      * can be added to this map. If the value is <strong>null</strong>, the key is removed from the internal map. This method can be
      * used by sub classes which also store properties in a map.
      *
      * @param key the key of the property
      * @param value the value of the property
      */
     protected void storeProperty(final String key, final Object value) {
         if (value == null) {
             properties.remove(key);
         } else {
             properties.put(key, value);
         }
     }
 }
	/*
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* https://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package org.apache.commons.configuration2.builder;

	import java.util.ArrayList;
	import java.util.Collection;
	import java.util.HashMap;
	import java.util.Map;

	import org.apache.commons.configuration2.ConfigurationDecoder;
	import org.apache.commons.configuration2.beanutils.BeanHelper;
	import org.apache.commons.configuration2.convert.ConversionHandler;
	import org.apache.commons.configuration2.convert.ListDelimiterHandler;
	import org.apache.commons.configuration2.interpol.ConfigurationInterpolator;
	import org.apache.commons.configuration2.interpol.InterpolatorSpecification;
	import org.apache.commons.configuration2.interpol.Lookup;
	import org.apache.commons.configuration2.io.ConfigurationLogger;
	import org.apache.commons.configuration2.sync.Synchronizer;

	/**
	* <p>
	* An implementation of {@code BuilderParameters} which handles the parameters of a {@link ConfigurationBuilder} common
	* to all concrete {@code Configuration} implementations.
	* </p>
	* <p>
	* This class provides methods for setting standard properties supported by the {@code AbstractConfiguration} base
	* class. A fluent interface can be used to set property values.
	* </p>
	* <p>
	* This class is not thread-safe. It is intended that an instance is constructed and initialized by a single thread
	* during configuration of a {@code ConfigurationBuilder}.
	* </p>
	*
	* @since 2.0
	*/
	public class BasicBuilderParameters implements Cloneable, BuilderParameters, BasicBuilderProperties<BasicBuilderParameters> {

	/** The key of the <em>throwExceptionOnMissing</em> property. */
	private static final String PROP_THROW_EXCEPTION_ON_MISSING = "throwExceptionOnMissing";

	/** The key of the <em>listDelimiterHandler</em> property. */
	private static final String PROP_LIST_DELIMITER_HANDLER = "listDelimiterHandler";

	/** The key of the <em>logger</em> property. */
	private static final String PROP_LOGGER = "logger";

	/** The key for the <em>interpolator</em> property. */
	private static final String PROP_INTERPOLATOR = "interpolator";

	/** The key for the <em>prefixLookups</em> property. */
	private static final String PROP_PREFIX_LOOKUPS = "prefixLookups";

	/** The key for the <em>defaultLookups</em> property. */
	private static final String PROP_DEFAULT_LOOKUPS = "defaultLookups";

	/** The key for the <em>parentInterpolator</em> property. */
	private static final String PROP_PARENT_INTERPOLATOR = "parentInterpolator";

	/** The key for the <em>synchronizer</em> property. */
	private static final String PROP_SYNCHRONIZER = "synchronizer";

	/** The key for the <em>conversionHandler</em> property. */
	private static final String PROP_CONVERSION_HANDLER = "conversionHandler";

	/** The key for the <em>configurationDecoder</em> property. */
	private static final String PROP_CONFIGURATION_DECODER = "configurationDecoder";

	/** The key for the {@code BeanHelper}. */
	private static final String PROP_BEAN_HELPER = RESERVED_PARAMETER_PREFIX + "BeanHelper";

	/**
	* Checks whether a map with parameters is present. Throws an exception if not.
	*
	* @param params the map with parameters to check
	* @throws IllegalArgumentException if the map is <strong>null</strong>
	*/
	private static void checkParameters(final Map<String, Object> params) {
	if (params == null) {
	throw new IllegalArgumentException("Parameters map must not be null!");
	}
	}

	/**
	* Creates defensive copies for collection structures when constructing the map with parameters. It should not be
	* possible to modify this object's internal state when having access to the parameters map.
	*
	* @param params the map with parameters to be passed to the caller
	*/
	private static void createDefensiveCopies(final HashMap<String, Object> params) {
	final Map<String, ? extends Lookup> prefixLookups = fetchPrefixLookups(params);
	if (prefixLookups != null) {
	params.put(PROP_PREFIX_LOOKUPS, new HashMap<>(prefixLookups));
	}
	final Collection<? extends Lookup> defLookups = fetchDefaultLookups(params);
	if (defLookups != null) {
	params.put(PROP_DEFAULT_LOOKUPS, new ArrayList<>(defLookups));
	}
	}

	/**
	* Tests whether the passed in map with parameters contains a valid collection with default lookups. This method works
	* like {@link #fetchAndCheckPrefixLookups(Map)}, but tests the default lookups collection.
	*
	* @param params the map with parameters
	* @return the collection with default lookups (may be <strong>null</strong>)
	* @throws IllegalArgumentException if invalid data is found
	*/
	private static Collection<? extends Lookup> fetchAndCheckDefaultLookups(final Map<String, Object> params) {
	final Collection<?> col = fetchParameter(params, PROP_DEFAULT_LOOKUPS, Collection.class);
	if (col == null) {
	return null;
	}

	if (col.stream().noneMatch(Lookup.class::isInstance)) {
	throw new IllegalArgumentException("Collection with default lookups contains invalid data: " + col);
	}
	return fetchDefaultLookups(params);
	}

	/**
	* Tests whether the passed in map with parameters contains a map with prefix lookups. This method is used if the
	* parameters map is from an insecure source and we cannot be sure that it contains valid data. Therefore, we have to
	* map that the key for the prefix lookups actually points to a map containing keys and values of expected data types.
	*
	* @param params the parameters map
	* @return the obtained map with prefix lookups
	* @throws IllegalArgumentException if the map contains invalid data
	*/
	private static Map<String, ? extends Lookup> fetchAndCheckPrefixLookups(final Map<String, Object> params) {
	final Map<?, ?> prefixes = fetchParameter(params, PROP_PREFIX_LOOKUPS, Map.class);
	if (prefixes == null) {
	return null;
	}
	prefixes.forEach((k, v) -> {
	if (!(k instanceof String) \|\| !(v instanceof Lookup)) {
	throw new IllegalArgumentException("Map with prefix lookups contains invalid data: " + prefixes);
	}
	});
	return fetchPrefixLookups(params);
	}

	/**
	* Obtains the {@code BeanHelper} object from the specified map with parameters. This method can be used to obtain an
	* instance from a parameters map that has been set via the {@code setBeanHelper()} method. If no such instance is
	* found, result is <strong>null</strong>.
	*
	* @param params the map with parameters (must not be <strong>null</strong>)
	* @return the {@code BeanHelper} stored in this map or <strong>null</strong>
	* @throws IllegalArgumentException if the map is <strong>null</strong>
	*/
	public static BeanHelper fetchBeanHelper(final Map<String, Object> params) {
	checkParameters(params);
	return (BeanHelper) params.get(PROP_BEAN_HELPER);
	}

	/**
	* Obtains the collection with default lookups from the parameters map.
	*
	* @param params the map with parameters
	* @return the collection with default lookups (may be <strong>null</strong>)
	*/
	private static Collection<? extends Lookup> fetchDefaultLookups(final Map<String, Object> params) {
	// This is safe to cast because we either have full control over the map
	// and thus know the types of the contained values or have checked
	// the content before
	@SuppressWarnings("unchecked")
	final Collection<? extends Lookup> defLookups = (Collection<? extends Lookup>) params.get(PROP_DEFAULT_LOOKUPS);
	return defLookups;
	}

	/**
	* Obtains a specification for a {@link ConfigurationInterpolator} from the specified map with parameters. All
	* properties related to interpolation are evaluated and added to the specification object.
	*
	* @param params the map with parameters (must not be <strong>null</strong>)
	* @return an {@code InterpolatorSpecification} object constructed with data from the map
	* @throws IllegalArgumentException if the map is <strong>null</strong> or contains invalid data
	*/
	public static InterpolatorSpecification fetchInterpolatorSpecification(final Map<String, Object> params) {
	checkParameters(params);
	return new InterpolatorSpecification.Builder().withInterpolator(fetchParameter(params, PROP_INTERPOLATOR, ConfigurationInterpolator.class))
	.withParentInterpolator(fetchParameter(params, PROP_PARENT_INTERPOLATOR, ConfigurationInterpolator.class))
	.withPrefixLookups(fetchAndCheckPrefixLookups(params)).withDefaultLookups(fetchAndCheckDefaultLookups(params)).create();
	}

	/**
	* Obtains a parameter from a map and performs a type check.
	*
	* @param params the map with parameters
	* @param key the key of the parameter
	* @param expClass the expected class of the parameter value
	* @param <T> the parameter type
	* @return the value of the parameter in the correct data type
	* @throws IllegalArgumentException if the parameter is not of the expected type
	*/
	private static <T> T fetchParameter(final Map<String, Object> params, final String key, final Class<T> expClass) {
	final Object value = params.get(key);
	if (value == null) {
	return null;
	}
	if (!expClass.isInstance(value)) {
	throw new IllegalArgumentException(String.format("Parameter %s is not of type %s!", key, expClass.getSimpleName()));
	}
	return expClass.cast(value);
	}

	/**
	* Obtains the map with prefix lookups from the parameters map.
	*
	* @param params the map with parameters
	* @return the map with prefix lookups (may be <strong>null</strong>)
	*/
	private static Map<String, ? extends Lookup> fetchPrefixLookups(final Map<String, Object> params) {
	// This is safe to cast because we either have full control over the map
	// and thus know the types of the contained values or have checked
	// the content before
	@SuppressWarnings("unchecked")
	final Map<String, ? extends Lookup> prefixLookups = (Map<String, ? extends Lookup>) params.get(PROP_PREFIX_LOOKUPS);
	return prefixLookups;
	}

	/** The map for storing the current property values. */
	private Map<String, Object> properties;

	/**
	* Creates a new instance of {@code BasicBuilderParameters}.
	*/
	public BasicBuilderParameters() {
	properties = new HashMap<>();
	}

	/**
	* Clones this object. This is useful because multiple builder instances may use a similar set of parameters. However,
	* single instances of parameter objects must not assigned to multiple builders. Therefore, cloning a parameters object
	* provides a solution for this use case. This method creates a new parameters object with the same content as this one.
	* The internal map storing the parameter values is cloned, too, also collection structures contained in this map.
	* However, no a full deep clone operation is performed. Objects like a {@code ConfigurationInterpolator} or
	* {@code Lookup}s are shared between this and the newly created instance.
	*
	* @return a clone of this object
	*/
	@Override
	public BasicBuilderParameters clone() {
	try {
	final BasicBuilderParameters copy = (BasicBuilderParameters) super.clone();
	copy.properties = getParameters();
	return copy;
	} catch (final CloneNotSupportedException cnex) {
	// should not happen
	throw new AssertionError(cnex);
	}
	}

	/**
	* Copies a number of properties from the given map into this object. Properties are only copied if they are defined in
	* the source map.
	*
	* @param source the source map
	* @param keys the keys to be copied
	*/
	protected void copyPropertiesFrom(final Map<String, ?> source, final String... keys) {
	for (final String key : keys) {
	final Object value = source.get(key);
	if (value != null) {
	storeProperty(key, value);
	}
	}
	}

	/**
	* Obtains the value of the specified property from the internal map. This method can be used by derived classes if a
	* specific property is to be accessed. If the given key is not found, result is <strong>null</strong>.
	*
	* @param key the key of the property in question
	* @return the value of the property with this key or <strong>null</strong>
	*/
	protected Object fetchProperty(final String key) {
	return properties.get(key);
	}

	/**
	* {@inheritDoc} This implementation returns a copy of the internal parameters map with the values set so far.
	* Collection structures (for example for lookup objects) are stored as defensive copies, so the original data cannot be
	* modified.
	*/
	@Override
	public Map<String, Object> getParameters() {
	final HashMap<String, Object> result = new HashMap<>(properties);
	if (result.containsKey(PROP_INTERPOLATOR)) {
	// A custom ConfigurationInterpolator overrides lookups
	result.remove(PROP_PREFIX_LOOKUPS);
	result.remove(PROP_DEFAULT_LOOKUPS);
	result.remove(PROP_PARENT_INTERPOLATOR);
	}

	createDefensiveCopies(result);
	return result;
	}

	/**
	* Inherits properties from the specified map. This can be used for instance to reuse parameters from one builder in
	* another builder - also in parent-child relations in which a parent builder creates child builders. The purpose of
	* this method is to let a concrete implementation decide which properties can be inherited. Because parameters are
	* basically organized as a map it would be possible to simply copy over all properties from the source object. However,
	* this is not appropriate in all cases. For instance, some properties - like a {@code ConfigurationInterpolator} - are
	* tightly connected to a configuration and cannot be reused in a different context. For other properties, for example a file
	* name, it does not make sense to copy it. Therefore, an implementation has to be explicit in the properties it wants
	* to take over.
	*
	* @param source the source properties to inherit from
	* @throws IllegalArgumentException if the source map is <strong>null</strong>
	*/
	public void inheritFrom(final Map<String, ?> source) {
	if (source == null) {
	throw new IllegalArgumentException("Source properties must not be null!");
	}
	copyPropertiesFrom(source, PROP_BEAN_HELPER, PROP_CONFIGURATION_DECODER, PROP_CONVERSION_HANDLER, PROP_LIST_DELIMITER_HANDLER, PROP_LOGGER,
	PROP_SYNCHRONIZER, PROP_THROW_EXCEPTION_ON_MISSING);
	}

	/**
	* Merges this object with the given parameters object. This method adds all property values defined by the passed in
	* parameters object to the internal storage which are not already in. So properties already defined in this object take
	* precedence. Property names starting with the reserved parameter prefix are ignored.
	*
	* @param p the object whose properties should be merged (must not be <strong>null</strong>)
	* @throws IllegalArgumentException if the passed in object is <strong>null</strong>
	*/
	public void merge(final BuilderParameters p) {
	if (p == null) {
	throw new IllegalArgumentException("Parameters to merge must not be null!");
	}
	p.getParameters().forEach((k, v) -> {
	if (!properties.containsKey(k) && !k.startsWith(RESERVED_PARAMETER_PREFIX)) {
	storeProperty(k, v);
	}
	});
	}

	/**
	* {@inheritDoc} This implementation stores the passed in {@code BeanHelper} object in the internal parameters map, but
	* uses a reserved key, so that it is not used for the initialization of properties of the managed configuration object.
	* The {@code fetchBeanHelper()} method can be used to obtain the {@code BeanHelper} instance from a parameters map.
	*/
	@Override
	public BasicBuilderParameters setBeanHelper(final BeanHelper beanHelper) {
	return setProperty(PROP_BEAN_HELPER, beanHelper);
	}

	/**
	* {@inheritDoc} This implementation stores the passed in {@code ConfigurationDecoder} object in the internal parameters
	* map.
	*/
	@Override
	public BasicBuilderParameters setConfigurationDecoder(final ConfigurationDecoder decoder) {
	return setProperty(PROP_CONFIGURATION_DECODER, decoder);
	}

	/**
	* {@inheritDoc} This implementation stores the passed in {@code ConversionHandler} object in the internal parameters
	* map.
	*/
	@Override
	public BasicBuilderParameters setConversionHandler(final ConversionHandler handler) {
	return setProperty(PROP_CONVERSION_HANDLER, handler);
	}

	/**
	* {@inheritDoc} A defensive copy of the passed in collection is created. A <strong>null</strong> argument causes all default
	* lookups to be removed from the internal parameters map.
	*/
	@Override
	public BasicBuilderParameters setDefaultLookups(final Collection<? extends Lookup> lookups) {
	if (lookups == null) {
	properties.remove(PROP_DEFAULT_LOOKUPS);
	return this;
	}
	return setProperty(PROP_DEFAULT_LOOKUPS, new ArrayList<>(lookups));
	}

	/**
	* {@inheritDoc} The passed in {@code ConfigurationInterpolator} is set without modifications.
	*/
	@Override
	public BasicBuilderParameters setInterpolator(final ConfigurationInterpolator ci) {
	return setProperty(PROP_INTERPOLATOR, ci);
	}

	/**
	* Sets the value of the <em>listDelimiterHandler</em> property. This property defines the object responsible for
	* dealing with list delimiter and escaping characters. Note:
	* {@link org.apache.commons.configuration2.AbstractConfiguration AbstractConfiguration} does not allow setting this
	* property to <strong>null</strong>. If the default {@code ListDelimiterHandler} is to be used, do not call this method.
	*
	* @param handler the {@code ListDelimiterHandler}
	* @return a reference to this object for method chaining
	*/
	@Override
	public BasicBuilderParameters setListDelimiterHandler(final ListDelimiterHandler handler) {
	return setProperty(PROP_LIST_DELIMITER_HANDLER, handler);
	}

	/**
	* Sets the <em>logger</em> property. With this property a concrete {@code Log} object can be set for the configuration.
	* Thus logging behavior can be controlled.
	*
	* @param log the {@code Log} for the configuration produced by this builder
	* @return a reference to this object for method chaining
	*/
	@Override
	public BasicBuilderParameters setLogger(final ConfigurationLogger log) {
	return setProperty(PROP_LOGGER, log);
	}

	/**
	* {@inheritDoc} This implementation stores the passed in {@code ConfigurationInterpolator} object in the internal
	* parameters map.
	*/
	@Override
	public BasicBuilderParameters setParentInterpolator(final ConfigurationInterpolator parent) {
	return setProperty(PROP_PARENT_INTERPOLATOR, parent);
	}

	/**
	* {@inheritDoc} A defensive copy of the passed in map is created. A <strong>null</strong> argument causes all prefix lookups to
	* be removed from the internal parameters map.
	*/
	@Override
	public BasicBuilderParameters setPrefixLookups(final Map<String, ? extends Lookup> lookups) {
	if (lookups == null) {
	properties.remove(PROP_PREFIX_LOOKUPS);
	return this;
	}
	return setProperty(PROP_PREFIX_LOOKUPS, new HashMap<>(lookups));
	}

	/**
	* Helper method for setting a property value.
	*
	* @param key the key of the property
	* @param value the value of the property
	* @return a reference to this object
	*/
	private BasicBuilderParameters setProperty(final String key, final Object value) {
	storeProperty(key, value);
	return this;
	}

	/**
	* {@inheritDoc} This implementation stores the passed in {@code Synchronizer} object in the internal parameters map.
	*/
	@Override
	public BasicBuilderParameters setSynchronizer(final Synchronizer sync) {
	return setProperty(PROP_SYNCHRONIZER, sync);
	}

	/**
	* Sets the value of the <em>throwExceptionOnMissing</em> property. This property controls the configuration's behavior
	* if missing properties are queried: a value of <strong>true</strong> causes the configuration to throw an exception, for a value
	* of <strong>false</strong> it will return <strong>null</strong> values. (Note: Methods returning a primitive data type will always throw
	* an exception if the property is not defined.)
	*
	* @param b the value of the property
	* @return a reference to this object for method chaining
	*/
	@Override
	public BasicBuilderParameters setThrowExceptionOnMissing(final boolean b) {
	return setProperty(PROP_THROW_EXCEPTION_ON_MISSING, Boolean.valueOf(b));
	}

	/**
	* Sets a property for this parameters object. Properties are stored in an internal map. With this method a new entry
	* can be added to this map. If the value is <strong>null</strong>, the key is removed from the internal map. This method can be
	* used by sub classes which also store properties in a map.
	*
	* @param key the key of the property
	* @param value the value of the property
	*/
	protected void storeProperty(final String key, final Object value) {
	if (value == null) {
	properties.remove(key);
	} else {
	properties.put(key, value);
	}
	}
	}