src/main/java/org/apache/commons/configuration2/tree/DefaultExpressionEngine.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
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 package org.apache.commons.configuration2.tree;

 import java.util.Collection;
 import java.util.LinkedList;
 import java.util.List;

 import org.apache.commons.lang3.StringUtils;

 /**
  * <p>
  * A default implementation of the {@code ExpressionEngine} interface providing the &quot;native&quot; expression
  * language for hierarchical configurations.
  * </p>
  * <p>
  * This class implements a rather simple expression language for navigating through a hierarchy of configuration nodes.
  * It supports the following operations:
  * </p>
  * <ul>
  * <li>Navigating from a node to one of its children using the child node delimiter, which is by the default a dot
  * (&quot;.&quot;).</li>
  * <li>Navigating from a node to one of its attributes using the attribute node delimiter, which by default follows the
  * XPATH like syntax {@code [@&lt;attributeName&gt;]}.</li>
  * <li>If there are multiple child or attribute nodes with the same name, a specific node can be selected using a
  * numerical index. By default indices are written in parenthesis.</li>
  * </ul>
  * <p>
  * As an example consider the following XML document:
  * </p>
  *
  * <pre>
  *  &lt;database&gt;
  *    &lt;tables&gt;
  *      &lt;table type=&quot;system&quot;&gt;
  *        &lt;name&gt;users&lt;/name&gt;
  *        &lt;fields&gt;
  *          &lt;field&gt;
  *            &lt;name&gt;lid&lt;/name&gt;
  *            &lt;type&gt;long&lt;/name&gt;
  *          &lt;/field&gt;
  *          &lt;field&gt;
  *            &lt;name&gt;usrName&lt;/name&gt;
  *            &lt;type&gt;java.lang.String&lt;/type&gt;
  *          &lt;/field&gt;
  *         ...
  *        &lt;/fields&gt;
  *      &lt;/table&gt;
  *      &lt;table&gt;
  *        &lt;name&gt;documents&lt;/name&gt;
  *        &lt;fields&gt;
  *          &lt;field&gt;
  *            &lt;name&gt;docid&lt;/name&gt;
  *            &lt;type&gt;long&lt;/type&gt;
  *          &lt;/field&gt;
  *          ...
  *        &lt;/fields&gt;
  *      &lt;/table&gt;
  *      ...
  *    &lt;/tables&gt;
  *  &lt;/database&gt;
  * </pre>
  *
  * <p>
  * If this document is parsed and stored in a hierarchical configuration object, for instance the key
  * {@code tables.table(0).name} can be used to find out the name of the first table. In opposite
  * {@code tables.table.name} would return a collection with the names of all available tables. Similarly the key
  * {@code tables.table(1).fields.field.name} returns a collection with the names of all fields of the second table. If
  * another index is added after the {@code field} element, a single field can be accessed:
  * {@code tables.table(1).fields.field(0).name}. The key {@code tables.table(0)[@type]} would select the type attribute
  * of the first table.
  * </p>
  * <p>
  * This example works with the default values for delimiters and index markers. It is also possible to set custom values
  * for these properties so that you can adapt a {@code DefaultExpressionEngine} to your personal needs.
  * </p>
  * <p>
  * The concrete symbols used by an instance are determined by a {@link DefaultExpressionEngineSymbols} object passed to
  * the constructor. By providing a custom symbols object the syntax for querying properties in a hierarchical
  * configuration can be altered.
  * </p>
  * <p>
  * Instances of this class are thread-safe and can be shared between multiple hierarchical configuration objects.
  * </p>
  *
  * @since 1.3
  */
 public class DefaultExpressionEngine implements ExpressionEngine {
     /**
      * A default instance of this class that is used as expression engine for hierarchical configurations per default.
      */
     public static final DefaultExpressionEngine INSTANCE = new DefaultExpressionEngine(DefaultExpressionEngineSymbols.DEFAULT_SYMBOLS);

     /** The symbols used by this instance. */
     private final DefaultExpressionEngineSymbols symbols;

     /** The matcher for node names. */
     private final NodeMatcher<String> nameMatcher;

     /**
      * Creates a new instance of {@code DefaultExpressionEngine} and initializes its symbols.
      *
      * @param syms the object with the symbols (must not be <b>null</b>)
      * @throws IllegalArgumentException if the symbols are <b>null</b>
      */
     public DefaultExpressionEngine(final DefaultExpressionEngineSymbols syms) {
         this(syms, null);
     }

     /**
      * Creates a new instance of {@code DefaultExpressionEngine} and initializes its symbols and the matcher for comparing
      * node names. The passed in matcher is always used when the names of nodes have to be matched against parts of
      * configuration keys.
      *
      * @param syms the object with the symbols (must not be <b>null</b>)
      * @param nodeNameMatcher the matcher for node names; can be <b>null</b>, then a default matcher is used
      * @throws IllegalArgumentException if the symbols are <b>null</b>
      */
     public DefaultExpressionEngine(final DefaultExpressionEngineSymbols syms, final NodeMatcher<String> nodeNameMatcher) {
         if (syms == null) {
             throw new IllegalArgumentException("Symbols must not be null!");
         }

         symbols = syms;
         nameMatcher = nodeNameMatcher != null ? nodeNameMatcher : NodeNameMatchers.EQUALS;
     }

     @Override
     public String attributeKey(final String parentKey, final String attributeName) {
         final DefaultConfigurationKey key = new DefaultConfigurationKey(this, parentKey);
         key.appendAttribute(attributeName);
         return key.toString();
     }

     /**
      * {@inheritDoc} This implementation works similar to {@code nodeKey()}; however, each key returned by this method has
      * an index (except for the root node). The parent key is prepended to the name of the current node in any case and
      * without further checks. If it is <b>null</b>, only the name of the current node with its index is returned.
      */
     @Override
     public <T> String canonicalKey(final T node, final String parentKey, final NodeHandler<T> handler) {
         final String nodeName = handler.nodeName(node);
         final T parent = handler.getParent(node);
         final DefaultConfigurationKey key = new DefaultConfigurationKey(this, parentKey);
         key.append(StringUtils.defaultString(nodeName));

         if (parent != null) {
             // this is not the root key
             key.appendIndex(determineIndex(node, parent, nodeName, handler));
         }
         return key.toString();
     }

     /**
      * Determines the index of the given node based on its parent node.
      *
      * @param node the current node
      * @param parent the parent node
      * @param nodeName the name of the current node
      * @param handler the node handler
      * @param <T> the type of the nodes to be dealt with
      * @return the index of this node
      */
     private <T> int determineIndex(final T node, final T parent, final String nodeName, final NodeHandler<T> handler) {
         return findChildNodesByName(handler, parent, nodeName).indexOf(node);
     }

     /**
      * Returns a list with all child nodes of the given parent node which match the specified node name. The match is done
      * using the current node name matcher.
      *
      * @param handler the {@code NodeHandler}
      * @param parent the parent node
      * @param nodeName the name of the current node
      * @param <T> the type of the nodes to be dealt with
      * @return a list with all matching child nodes
      */
     private <T> List<T> findChildNodesByName(final NodeHandler<T> handler, final T parent, final String nodeName) {
         return handler.getMatchingChildren(parent, nameMatcher, nodeName);
     }

     /**
      * Finds the last existing node for an add operation. This method traverses the node tree along the specified key. The
      * last existing node on this path is returned.
      *
      * @param <T> the type of the nodes to be dealt with
      * @param keyIt the key iterator
      * @param node the current node
      * @param handler the node handler
      * @return the last existing node on the given path
      */
     protected <T> T findLastPathNode(final DefaultConfigurationKey.KeyIterator keyIt, final T node, final NodeHandler<T> handler) {
         final String keyPart = keyIt.nextKey(false);

         if (keyIt.hasNext()) {
             if (!keyIt.isPropertyKey()) {
                 // Attribute keys can only appear as last elements of the path
                 throw new IllegalArgumentException("Invalid path for add operation: " + "Attribute key in the middle!");
             }
             final int idx = keyIt.hasIndex() ? keyIt.getIndex() : handler.getMatchingChildrenCount(node, nameMatcher, keyPart) - 1;
             if (idx < 0 || idx >= handler.getMatchingChildrenCount(node, nameMatcher, keyPart)) {
                 return node;
             }
             return findLastPathNode(keyIt, findChildNodesByName(handler, node, keyPart).get(idx), handler);
         }
         return node;
     }

     /**
      * Recursive helper method for evaluating a key. This method processes all facets of a configuration key, traverses the
      * tree of properties and fetches the results of all matching properties.
      *
      * @param <T> the type of nodes to be dealt with
      * @param keyPart the configuration key iterator
      * @param node the current node
      * @param results here the found results are stored
      * @param handler the node handler
      */
     protected <T> void findNodesForKey(final DefaultConfigurationKey.KeyIterator keyPart, final T node, final Collection<QueryResult<T>> results,
         final NodeHandler<T> handler) {
         if (!keyPart.hasNext()) {
             results.add(QueryResult.createNodeResult(node));
         } else {
             final String key = keyPart.nextKey(false);
             if (keyPart.isPropertyKey()) {
                 processSubNodes(keyPart, findChildNodesByName(handler, node, key), results, handler);
             }
             if (keyPart.isAttribute() && !keyPart.hasNext() && handler.getAttributeValue(node, key) != null) {
                 results.add(QueryResult.createAttributeResult(node, key));
             }
         }
     }

     /**
      * Gets the {@code DefaultExpressionEngineSymbols} object associated with this instance.
      *
      * @return the {@code DefaultExpressionEngineSymbols} used by this engine
      * @since 2.0
      */
     public DefaultExpressionEngineSymbols getSymbols() {
         return symbols;
     }

     /**
      * {@inheritDoc} This implementation takes the given parent key, adds a property delimiter, and then adds the node's
      * name. The name of the root node is a blank string. Note that no indices are returned.
      */
     @Override
     public <T> String nodeKey(final T node, final String parentKey, final NodeHandler<T> handler) {
         if (parentKey == null) {
             // this is the root node
             return StringUtils.EMPTY;
         }
         final DefaultConfigurationKey key = new DefaultConfigurationKey(this, parentKey);
         key.append(handler.nodeName(node), true);
         return key.toString();
     }

     /**
      * <p>
      * Prepares Adding the property with the specified key.
      * </p>
      * <p>
      * To be able to deal with the structure supported by hierarchical configuration implementations the passed in key is of
      * importance, especially the indices it might contain. The following example should clarify this: Suppose the current
      * node structure looks like the following:
      * </p>
      *
      * <pre>
      *  tables
      *     +-- table
      *             +-- name = user
      *             +-- fields
      *                     +-- field
      *                             +-- name = uid
      *                     +-- field
      *                             +-- name = firstName
      *                     ...
      *     +-- table
      *             +-- name = documents
      *             +-- fields
      *                    ...
      * </pre>
      * <p>
      * In this example a database structure is defined, e.g. all fields of the first table could be accessed using the key
      * {@code tables.table(0).fields.field.name}. If now properties are to be added, it must be exactly specified at which
      * position in the hierarchy the new property is to be inserted. So to add a new field name to a table it is not enough
      * to say just
      * </p>
      *
      * <pre>
      * config.addProperty(&quot;tables.table.fields.field.name&quot;, &quot;newField&quot;);
      * </pre>
      * <p>
      * The statement given above contains some ambiguity. For instance it is not clear, to which table the new field should
      * be added. If this method finds such an ambiguity, it is resolved by following the last valid path. Here this would be
      * the last table. The same is true for the {@code field}; because there are multiple fields and no explicit index is
      * provided, a new {@code name} property would be added to the last field - which is probably not what was desired.
      * </p>
      * <p>
      * To make things clear explicit indices should be provided whenever possible. In the example above the exact table
      * could be specified by providing an index for the {@code table} element as in {@code tables.table(1).fields}. By
      * specifying an index it can also be expressed that at a given position in the configuration tree a new branch should
      * be added. In the example above we did not want to add an additional {@code name} element to the last field of the
      * table, but we want a complete new {@code field} element. This can be achieved by specifying an invalid index (like
      * -1) after the element where a new branch should be created. Given this our example would run:
      * </p>
      *
      * <pre>
      * config.addProperty(&quot;tables.table(1).fields.field(-1).name&quot;, &quot;newField&quot;);
      * </pre>
      * <p>
      * With this notation it is possible to add new branches everywhere. We could for instance create a new {@code table}
      * element by specifying
      * </p>
      *
      * <pre>
      * config.addProperty(&quot;tables.table(-1).fields.field.name&quot;, &quot;newField2&quot;);
      * </pre>
      * <p>
      * (Note that because after the {@code table} element a new branch is created indices in following elements are not
      * relevant; the branch is new so there cannot be any ambiguities.)
      * </p>
      *
      * @param <T> the type of the nodes to be dealt with
      * @param root the root node of the nodes hierarchy
      * @param key the key of the new property
      * @param handler the node handler
      * @return a data object with information needed for the add operation
      */
     @Override
     public <T> NodeAddData<T> prepareAdd(final T root, final String key, final NodeHandler<T> handler) {
         final DefaultConfigurationKey.KeyIterator it = new DefaultConfigurationKey(this, key).iterator();
         if (!it.hasNext()) {
             throw new IllegalArgumentException("Key for add operation must be defined!");
         }

         final T parent = findLastPathNode(it, root, handler);
         final List<String> pathNodes = new LinkedList<>();

         while (it.hasNext()) {
             if (!it.isPropertyKey()) {
                 throw new IllegalArgumentException("Invalid key for add operation: " + key + " (Attribute key in the middle.)");
             }
             pathNodes.add(it.currentKey());
             it.next();
         }

         return new NodeAddData<>(parent, it.currentKey(), !it.isPropertyKey(), pathNodes);
     }

     /**
      * Called by {@code findNodesForKey()} to process the sub nodes of the current node depending on the type of the current
      * key part (children, attributes, or both).
      *
      * @param <T> the type of the nodes to be dealt with
      * @param keyPart the key part
      * @param subNodes a list with the sub nodes to process
      * @param nodes the target collection
      * @param handler the node handler
      */
     private <T> void processSubNodes(final DefaultConfigurationKey.KeyIterator keyPart, final List<T> subNodes, final Collection<QueryResult<T>> nodes,
         final NodeHandler<T> handler) {
         if (keyPart.hasIndex()) {
             if (keyPart.getIndex() >= 0 && keyPart.getIndex() < subNodes.size()) {
                 findNodesForKey((DefaultConfigurationKey.KeyIterator) keyPart.clone(), subNodes.get(keyPart.getIndex()), nodes, handler);
             }
         } else {
             subNodes.forEach(node -> findNodesForKey((DefaultConfigurationKey.KeyIterator) keyPart.clone(), node, nodes, handler));
         }
     }

     /**
      * {@inheritDoc} This method supports the syntax as described in the class comment.
      */
     @Override
     public <T> List<QueryResult<T>> query(final T root, final String key, final NodeHandler<T> handler) {
         final List<QueryResult<T>> results = new LinkedList<>();
         findNodesForKey(new DefaultConfigurationKey(this, key).iterator(), root, results, handler);
         return results;
     }
 }
	/*
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/
	package org.apache.commons.configuration2.tree;

	import java.util.Collection;
	import java.util.LinkedList;
	import java.util.List;

	import org.apache.commons.lang3.StringUtils;

	/**
	* <p>
	* A default implementation of the {@code ExpressionEngine} interface providing the "native" expression
	* language for hierarchical configurations.
	* </p>
	* <p>
	* This class implements a rather simple expression language for navigating through a hierarchy of configuration nodes.
	* It supports the following operations:
	* </p>
	* <ul>
	* <li>Navigating from a node to one of its children using the child node delimiter, which is by the default a dot
	* (".").</li>
	* <li>Navigating from a node to one of its attributes using the attribute node delimiter, which by default follows the
	* XPATH like syntax {@code [@<attributeName>]}.</li>
	* <li>If there are multiple child or attribute nodes with the same name, a specific node can be selected using a
	* numerical index. By default indices are written in parenthesis.</li>
	* </ul>
	* <p>
	* As an example consider the following XML document:
	* </p>
	*
	* <pre>
	* <database>
	* <tables>
	* <table type="system">
	* <name>users</name>
	* <fields>
	* <field>
	* <name>lid</name>
	* <type>long</name>
	* </field>
	* <field>
	* <name>usrName</name>
	* <type>java.lang.String</type>
	* </field>
	* ...
	* </fields>
	* </table>
	* <table>
	* <name>documents</name>
	* <fields>
	* <field>
	* <name>docid</name>
	* <type>long</type>
	* </field>
	* ...
	* </fields>
	* </table>
	* ...
	* </tables>
	* </database>
	* </pre>
	*
	* <p>
	* If this document is parsed and stored in a hierarchical configuration object, for instance the key
	* {@code tables.table(0).name} can be used to find out the name of the first table. In opposite
	* {@code tables.table.name} would return a collection with the names of all available tables. Similarly the key
	* {@code tables.table(1).fields.field.name} returns a collection with the names of all fields of the second table. If
	* another index is added after the {@code field} element, a single field can be accessed:
	* {@code tables.table(1).fields.field(0).name}. The key {@code tables.table(0)[@type]} would select the type attribute
	* of the first table.
	* </p>
	* <p>
	* This example works with the default values for delimiters and index markers. It is also possible to set custom values
	* for these properties so that you can adapt a {@code DefaultExpressionEngine} to your personal needs.
	* </p>
	* <p>
	* The concrete symbols used by an instance are determined by a {@link DefaultExpressionEngineSymbols} object passed to
	* the constructor. By providing a custom symbols object the syntax for querying properties in a hierarchical
	* configuration can be altered.
	* </p>
	* <p>
	* Instances of this class are thread-safe and can be shared between multiple hierarchical configuration objects.
	* </p>
	*
	* @since 1.3
	*/
	public class DefaultExpressionEngine implements ExpressionEngine {
	/**
	* A default instance of this class that is used as expression engine for hierarchical configurations per default.
	*/
	public static final DefaultExpressionEngine INSTANCE = new DefaultExpressionEngine(DefaultExpressionEngineSymbols.DEFAULT_SYMBOLS);

	/** The symbols used by this instance. */
	private final DefaultExpressionEngineSymbols symbols;

	/** The matcher for node names. */
	private final NodeMatcher<String> nameMatcher;

	/**
	* Creates a new instance of {@code DefaultExpressionEngine} and initializes its symbols.
	*
	* @param syms the object with the symbols (must not be <b>null</b>)
	* @throws IllegalArgumentException if the symbols are <b>null</b>
	*/
	public DefaultExpressionEngine(final DefaultExpressionEngineSymbols syms) {
	this(syms, null);
	}

	/**
	* Creates a new instance of {@code DefaultExpressionEngine} and initializes its symbols and the matcher for comparing
	* node names. The passed in matcher is always used when the names of nodes have to be matched against parts of
	* configuration keys.
	*
	* @param syms the object with the symbols (must not be <b>null</b>)
	* @param nodeNameMatcher the matcher for node names; can be <b>null</b>, then a default matcher is used
	* @throws IllegalArgumentException if the symbols are <b>null</b>
	*/
	public DefaultExpressionEngine(final DefaultExpressionEngineSymbols syms, final NodeMatcher<String> nodeNameMatcher) {
	if (syms == null) {
	throw new IllegalArgumentException("Symbols must not be null!");
	}

	symbols = syms;
	nameMatcher = nodeNameMatcher != null ? nodeNameMatcher : NodeNameMatchers.EQUALS;
	}

	@Override
	public String attributeKey(final String parentKey, final String attributeName) {
	final DefaultConfigurationKey key = new DefaultConfigurationKey(this, parentKey);
	key.appendAttribute(attributeName);
	return key.toString();
	}

	/**
	* {@inheritDoc} This implementation works similar to {@code nodeKey()}; however, each key returned by this method has
	* an index (except for the root node). The parent key is prepended to the name of the current node in any case and
	* without further checks. If it is <b>null</b>, only the name of the current node with its index is returned.
	*/
	@Override
	public <T> String canonicalKey(final T node, final String parentKey, final NodeHandler<T> handler) {
	final String nodeName = handler.nodeName(node);
	final T parent = handler.getParent(node);
	final DefaultConfigurationKey key = new DefaultConfigurationKey(this, parentKey);
	key.append(StringUtils.defaultString(nodeName));

	if (parent != null) {
	// this is not the root key
	key.appendIndex(determineIndex(node, parent, nodeName, handler));
	}
	return key.toString();
	}

	/**
	* Determines the index of the given node based on its parent node.
	*
	* @param node the current node
	* @param parent the parent node
	* @param nodeName the name of the current node
	* @param handler the node handler
	* @param <T> the type of the nodes to be dealt with
	* @return the index of this node
	*/
	private <T> int determineIndex(final T node, final T parent, final String nodeName, final NodeHandler<T> handler) {
	return findChildNodesByName(handler, parent, nodeName).indexOf(node);
	}

	/**
	* Returns a list with all child nodes of the given parent node which match the specified node name. The match is done
	* using the current node name matcher.
	*
	* @param handler the {@code NodeHandler}
	* @param parent the parent node
	* @param nodeName the name of the current node
	* @param <T> the type of the nodes to be dealt with
	* @return a list with all matching child nodes
	*/
	private <T> List<T> findChildNodesByName(final NodeHandler<T> handler, final T parent, final String nodeName) {
	return handler.getMatchingChildren(parent, nameMatcher, nodeName);
	}

	/**
	* Finds the last existing node for an add operation. This method traverses the node tree along the specified key. The
	* last existing node on this path is returned.
	*
	* @param <T> the type of the nodes to be dealt with
	* @param keyIt the key iterator
	* @param node the current node
	* @param handler the node handler
	* @return the last existing node on the given path
	*/
	protected <T> T findLastPathNode(final DefaultConfigurationKey.KeyIterator keyIt, final T node, final NodeHandler<T> handler) {
	final String keyPart = keyIt.nextKey(false);

	if (keyIt.hasNext()) {
	if (!keyIt.isPropertyKey()) {
	// Attribute keys can only appear as last elements of the path
	throw new IllegalArgumentException("Invalid path for add operation: " + "Attribute key in the middle!");
	}
	final int idx = keyIt.hasIndex() ? keyIt.getIndex() : handler.getMatchingChildrenCount(node, nameMatcher, keyPart) - 1;
	if (idx < 0 \|\| idx >= handler.getMatchingChildrenCount(node, nameMatcher, keyPart)) {
	return node;
	}
	return findLastPathNode(keyIt, findChildNodesByName(handler, node, keyPart).get(idx), handler);
	}
	return node;
	}

	/**
	* Recursive helper method for evaluating a key. This method processes all facets of a configuration key, traverses the
	* tree of properties and fetches the results of all matching properties.
	*
	* @param <T> the type of nodes to be dealt with
	* @param keyPart the configuration key iterator
	* @param node the current node
	* @param results here the found results are stored
	* @param handler the node handler
	*/
	protected <T> void findNodesForKey(final DefaultConfigurationKey.KeyIterator keyPart, final T node, final Collection<QueryResult<T>> results,
	final NodeHandler<T> handler) {
	if (!keyPart.hasNext()) {
	results.add(QueryResult.createNodeResult(node));
	} else {
	final String key = keyPart.nextKey(false);
	if (keyPart.isPropertyKey()) {
	processSubNodes(keyPart, findChildNodesByName(handler, node, key), results, handler);
	}
	if (keyPart.isAttribute() && !keyPart.hasNext() && handler.getAttributeValue(node, key) != null) {
	results.add(QueryResult.createAttributeResult(node, key));
	}
	}
	}

	/**
	* Gets the {@code DefaultExpressionEngineSymbols} object associated with this instance.
	*
	* @return the {@code DefaultExpressionEngineSymbols} used by this engine
	* @since 2.0
	*/
	public DefaultExpressionEngineSymbols getSymbols() {
	return symbols;
	}

	/**
	* {@inheritDoc} This implementation takes the given parent key, adds a property delimiter, and then adds the node's
	* name. The name of the root node is a blank string. Note that no indices are returned.
	*/
	@Override
	public <T> String nodeKey(final T node, final String parentKey, final NodeHandler<T> handler) {
	if (parentKey == null) {
	// this is the root node
	return StringUtils.EMPTY;
	}
	final DefaultConfigurationKey key = new DefaultConfigurationKey(this, parentKey);
	key.append(handler.nodeName(node), true);
	return key.toString();
	}

	/**
	* <p>
	* Prepares Adding the property with the specified key.
	* </p>
	* <p>
	* To be able to deal with the structure supported by hierarchical configuration implementations the passed in key is of
	* importance, especially the indices it might contain. The following example should clarify this: Suppose the current
	* node structure looks like the following:
	* </p>
	*
	* <pre>
	* tables
	* +-- table
	* +-- name = user
	* +-- fields
	* +-- field
	* +-- name = uid
	* +-- field
	* +-- name = firstName
	* ...
	* +-- table
	* +-- name = documents
	* +-- fields
	* ...
	* </pre>
	* <p>
	* In this example a database structure is defined, e.g. all fields of the first table could be accessed using the key
	* {@code tables.table(0).fields.field.name}. If now properties are to be added, it must be exactly specified at which
	* position in the hierarchy the new property is to be inserted. So to add a new field name to a table it is not enough
	* to say just
	* </p>
	*
	* <pre>
	* config.addProperty("tables.table.fields.field.name", "newField");
	* </pre>
	* <p>
	* The statement given above contains some ambiguity. For instance it is not clear, to which table the new field should
	* be added. If this method finds such an ambiguity, it is resolved by following the last valid path. Here this would be
	* the last table. The same is true for the {@code field}; because there are multiple fields and no explicit index is
	* provided, a new {@code name} property would be added to the last field - which is probably not what was desired.
	* </p>
	* <p>
	* To make things clear explicit indices should be provided whenever possible. In the example above the exact table
	* could be specified by providing an index for the {@code table} element as in {@code tables.table(1).fields}. By
	* specifying an index it can also be expressed that at a given position in the configuration tree a new branch should
	* be added. In the example above we did not want to add an additional {@code name} element to the last field of the
	* table, but we want a complete new {@code field} element. This can be achieved by specifying an invalid index (like
	* -1) after the element where a new branch should be created. Given this our example would run:
	* </p>
	*
	* <pre>
	* config.addProperty("tables.table(1).fields.field(-1).name", "newField");
	* </pre>
	* <p>
	* With this notation it is possible to add new branches everywhere. We could for instance create a new {@code table}
	* element by specifying
	* </p>
	*
	* <pre>
	* config.addProperty("tables.table(-1).fields.field.name", "newField2");
	* </pre>
	* <p>
	* (Note that because after the {@code table} element a new branch is created indices in following elements are not
	* relevant; the branch is new so there cannot be any ambiguities.)
	* </p>
	*
	* @param <T> the type of the nodes to be dealt with
	* @param root the root node of the nodes hierarchy
	* @param key the key of the new property
	* @param handler the node handler
	* @return a data object with information needed for the add operation
	*/
	@Override
	public <T> NodeAddData<T> prepareAdd(final T root, final String key, final NodeHandler<T> handler) {
	final DefaultConfigurationKey.KeyIterator it = new DefaultConfigurationKey(this, key).iterator();
	if (!it.hasNext()) {
	throw new IllegalArgumentException("Key for add operation must be defined!");
	}

	final T parent = findLastPathNode(it, root, handler);
	final List<String> pathNodes = new LinkedList<>();

	while (it.hasNext()) {
	if (!it.isPropertyKey()) {
	throw new IllegalArgumentException("Invalid key for add operation: " + key + " (Attribute key in the middle.)");
	}
	pathNodes.add(it.currentKey());
	it.next();
	}

	return new NodeAddData<>(parent, it.currentKey(), !it.isPropertyKey(), pathNodes);
	}

	/**
	* Called by {@code findNodesForKey()} to process the sub nodes of the current node depending on the type of the current
	* key part (children, attributes, or both).
	*
	* @param <T> the type of the nodes to be dealt with
	* @param keyPart the key part
	* @param subNodes a list with the sub nodes to process
	* @param nodes the target collection
	* @param handler the node handler
	*/
	private <T> void processSubNodes(final DefaultConfigurationKey.KeyIterator keyPart, final List<T> subNodes, final Collection<QueryResult<T>> nodes,
	final NodeHandler<T> handler) {
	if (keyPart.hasIndex()) {
	if (keyPart.getIndex() >= 0 && keyPart.getIndex() < subNodes.size()) {
	findNodesForKey((DefaultConfigurationKey.KeyIterator) keyPart.clone(), subNodes.get(keyPart.getIndex()), nodes, handler);
	}
	} else {
	subNodes.forEach(node -> findNodesForKey((DefaultConfigurationKey.KeyIterator) keyPart.clone(), node, nodes, handler));
	}
	}

	/**
	* {@inheritDoc} This method supports the syntax as described in the class comment.
	*/
	@Override
	public <T> List<QueryResult<T>> query(final T root, final String key, final NodeHandler<T> handler) {
	final List<QueryResult<T>> results = new LinkedList<>();
	findNodesForKey(new DefaultConfigurationKey(this, key).iterator(), root, results, handler);
	return results;
	}
	}