    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 */
    017
    018package org.apache.commons.configuration2;
    019
    020import java.io.IOException;
    021import java.io.InputStream;
    022import java.io.Reader;
    023import java.io.StringReader;
    024import java.io.StringWriter;
    025import java.io.Writer;
    026import java.net.URL;
    027import java.util.ArrayList;
    028import java.util.Collection;
    029import java.util.Collections;
    030import java.util.HashMap;
    031import java.util.Iterator;
    032import java.util.Map;
    033
    034import javax.xml.parsers.DocumentBuilder;
    035import javax.xml.parsers.DocumentBuilderFactory;
    036import javax.xml.parsers.ParserConfigurationException;
    037import javax.xml.transform.OutputKeys;
    038import javax.xml.transform.Result;
    039import javax.xml.transform.Source;
    040import javax.xml.transform.Transformer;
    041import javax.xml.transform.dom.DOMSource;
    042import javax.xml.transform.stream.StreamResult;
    043
    044import org.apache.commons.configuration2.convert.ListDelimiterHandler;
    045import org.apache.commons.configuration2.ex.ConfigurationException;
    046import org.apache.commons.configuration2.io.ConfigurationLogger;
    047import org.apache.commons.configuration2.io.FileLocator;
    048import org.apache.commons.configuration2.io.FileLocatorAware;
    049import org.apache.commons.configuration2.io.InputStreamSupport;
    050import org.apache.commons.configuration2.resolver.DefaultEntityResolver;
    051import org.apache.commons.configuration2.tree.ImmutableNode;
    052import org.apache.commons.configuration2.tree.NodeTreeWalker;
    053import org.apache.commons.configuration2.tree.ReferenceNodeHandler;
    054import org.apache.commons.lang3.StringUtils;
    055import org.apache.commons.lang3.mutable.MutableObject;
    056import org.w3c.dom.Attr;
    057import org.w3c.dom.CDATASection;
    058import org.w3c.dom.Document;
    059import org.w3c.dom.Element;
    060import org.w3c.dom.NamedNodeMap;
    061import org.w3c.dom.Node;
    062import org.w3c.dom.NodeList;
    063import org.w3c.dom.Text;
    064import org.xml.sax.EntityResolver;
    065import org.xml.sax.InputSource;
    066import org.xml.sax.SAXException;
    067import org.xml.sax.SAXParseException;
    068import org.xml.sax.helpers.DefaultHandler;
    069
    070/**
    071 * <p>
    072 * A specialized hierarchical configuration class that is able to parse XML documents.
    073 * </p>
    074 * <p>
    075 * The parsed document will be stored keeping its structure. The class also tries to preserve as much information from
    076 * the loaded XML document as possible, including comments and processing instructions. These will be contained in
    077 * documents created by the {@code save()} methods, too.
    078 * </p>
    079 * <p>
    080 * Like other file based configuration classes this class maintains the name and path to the loaded configuration file.
    081 * These properties can be altered using several setter methods, but they are not modified by {@code save()} and
    082 * {@code load()} methods. If XML documents contain relative paths to other documents (for example to a DTD), these references
    083 * are resolved based on the path set for this configuration.
    084 * </p>
    085 * <p>
    086 * By inheriting from {@link AbstractConfiguration} this class provides some extended functionality, for example interpolation
    087 * of property values. Like in {@link PropertiesConfiguration} property values can contain delimiter characters (the
    088 * comma ',' per default) and are then split into multiple values. This works for XML attributes and text content of
    089 * elements as well. The delimiter can be escaped by a backslash. As an example consider the following XML fragment:
    090 * </p>
    091 *
    092 * <pre>
    093 * &lt;config&gt;
    094 *   &lt;array&gt;10,20,30,40&lt;/array&gt;
    095 *   &lt;scalar&gt;3\,1415&lt;/scalar&gt;
    096 *   &lt;cite text="To be or not to be\, this is the question!"/&gt;
    097 * &lt;/config&gt;
    098 * </pre>
    099 *
    100 * <p>
    101 * Here the content of the {@code array} element will be split at the commas, so the {@code array} key will be assigned
    102 * 4 values. In the {@code scalar} property and the {@code text} attribute of the {@code cite} element the comma is
    103 * escaped, so that no splitting is performed.
    104 * </p>
    105 * <p>
    106 * The configuration API allows setting multiple values for a single attribute, for example something like the following is
    107 * legal (assuming that the default expression engine is used):
    108 * </p>
    109 *
    110 * <pre>
    111 * XMLConfiguration config = new XMLConfiguration();
    112 * config.addProperty(&quot;test.dir[@name]&quot;, &quot;C:\\Temp\\&quot;);
    113 * config.addProperty(&quot;test.dir[@name]&quot;, &quot;D:\\Data\\&quot;);
    114 * </pre>
    115 *
    116 * <p>
    117 * However, in XML such a constellation is not supported; an attribute can appear only once for a single element.
    118 * Therefore, an attempt to save a configuration which violates this condition will throw an exception.
    119 * </p>
    120 * <p>
    121 * Like other {@code Configuration} implementations, {@code XMLConfiguration} uses a {@link ListDelimiterHandler} object
    122 * for controlling list split operations. Per default, a list delimiter handler object is set which disables this
    123 * feature. XML has a built-in support for complex structures including list properties; therefore, list splitting is
    124 * not that relevant for this configuration type. Nevertheless, by setting an alternative {@code ListDelimiterHandler}
    125 * implementation, this feature can be enabled. It works as for any other concrete {@code Configuration} implementation.
    126 * </p>
    127 * <p>
    128 * Whitespace in the content of XML documents is trimmed per default. In most cases this is desired. However, sometimes
    129 * whitespace is indeed important and should be treated as part of the value of a property as in the following example:
    130 * </p>
    131 *
    132 * <pre>
    133 *   &lt;indent&gt;    &lt;/indent&gt;
    134 * </pre>
    135 *
    136 * <p>
    137 * Per default the spaces in the {@code indent} element will be trimmed resulting in an empty element. To tell
    138 * {@code XMLConfiguration} that spaces are relevant the {@code xml:space} attribute can be used, which is defined in
    139 * the <a href="http://www.w3.org/TR/REC-xml/#sec-white-space">XML specification</a>. This will look as follows:
    140 * </p>
    141 *
    142 * <pre>
    143 *   &lt;indent <strong>xml:space=&quot;preserve&quot;</strong>&gt;    &lt;/indent&gt;
    144 * </pre>
    145 *
    146 * <p>
    147 * The value of the {@code indent} property will now contain the spaces.
    148 * </p>
    149 * <p>
    150 * {@code XMLConfiguration} implements the {@link FileBasedConfiguration} interface and thus can be used together with a
    151 * file-based builder to load XML configuration files from various sources like files, URLs, or streams.
    152 * </p>
    153 * <p>
    154 * Like other {@code Configuration} implementations, this class uses a {@code Synchronizer} object to control concurrent
    155 * access. By choosing a suitable implementation of the {@code Synchronizer} interface, an instance can be made
    156 * thread-safe or not. Note that access to most of the properties typically set through a builder is not protected by
    157 * the {@code Synchronizer}. The intended usage is that these properties are set once at construction time through the
    158 * builder and after that remain constant. If you wish to change such properties during life time of an instance, you
    159 * have to use the {@code lock()} and {@code unlock()} methods manually to ensure that other threads see your changes.
    160 * </p>
    161 * <p>
    162 * More information about the basic functionality supported by {@code XMLConfiguration} can be found at the user's guide
    163 * at <a href="https://commons.apache.org/proper/commons-configuration/userguide/howto_basicfeatures.html"> Basic
    164 * features and AbstractConfiguration</a>. There is also a separate chapter dealing with
    165 * <a href="commons.apache.org/proper/commons-configuration/userguide/howto_xml.html"> XML Configurations</a> in
    166 * special.
    167 * </p>
    168 *
    169 * @since 1.0
    170 */
    171public class XMLConfiguration extends BaseHierarchicalConfiguration implements FileBasedConfiguration, FileLocatorAware, InputStreamSupport {
    172    /**
    173     * A concrete {@code BuilderVisitor} that can construct XML documents.
    174     */
    175    static class XMLBuilderVisitor extends BuilderVisitor {
    176        /**
    177         * Removes all attributes of the given element.
    178         *
    179         * @param elem the element
    180         */
    181        private static void clearAttributes(final Element elem) {
    182            final NamedNodeMap attributes = elem.getAttributes();
    183            for (int i = 0; i < attributes.getLength(); i++) {
    184                elem.removeAttribute(attributes.item(i).getNodeName());
    185            }
    186        }
    187
    188        /**
    189         * Returns the only text node of an element for update. This method is called when the element's text changes. Then all
    190         * text nodes except for the first are removed. A reference to the first is returned or <strong>null</strong> if there is no text
    191         * node at all.
    192         *
    193         * @param elem the element
    194         * @return the first and only text node
    195         */
    196        private static Text findTextNodeForUpdate(final Element elem) {
    197            Text result = null;
    198            // Find all Text nodes
    199            final NodeList children = elem.getChildNodes();
    200            final Collection<Node> textNodes = new ArrayList<>();
    201            for (int i = 0; i < children.getLength(); i++) {
    202                final Node nd = children.item(i);
    203                if (nd instanceof Text) {
    204                    if (result == null) {
    205                        result = (Text) nd;
    206                    } else {
    207                        textNodes.add(nd);
    208                    }
    209                }
    210            }
    211
    212            // We don't want CDATAs
    213            if (result instanceof CDATASection) {
    214                textNodes.add(result);
    215                result = null;
    216            }
    217
    218            // Remove all but the first Text node
    219            textNodes.forEach(elem::removeChild);
    220            return result;
    221        }
    222
    223        /**
    224         * Helper method for updating the values of all attributes of the specified node.
    225         *
    226         * @param node the affected node
    227         * @param elem the element that is associated with this node
    228         */
    229        private static void updateAttributes(final ImmutableNode node, final Element elem) {
    230            if (node != null && elem != null) {
    231                clearAttributes(elem);
    232                node.getAttributes().forEach((k, v) -> {
    233                    if (v != null) {
    234                        elem.setAttribute(k, v.toString());
    235                    }
    236                });
    237            }
    238        }
    239
    240        /** Stores the document to be constructed. */
    241        private final Document document;
    242
    243        /** The element mapping. */
    244        private final Map<Node, Node> elementMapping;
    245
    246        /** A mapping for the references for new nodes. */
    247        private final Map<ImmutableNode, Element> newElements;
    248
    249        /** Stores the list delimiter handler . */
    250        private final ListDelimiterHandler listDelimiterHandler;
    251
    252        /**
    253         * Creates a new instance of {@code XMLBuilderVisitor}.
    254         *
    255         * @param docHelper the document helper
    256         * @param handler the delimiter handler for properties with multiple values
    257         */
    258        public XMLBuilderVisitor(final XMLDocumentHelper docHelper, final ListDelimiterHandler handler) {
    259            document = docHelper.getDocument();
    260            elementMapping = docHelper.getElementMapping();
    261            listDelimiterHandler = handler;
    262            newElements = new HashMap<>();
    263        }
    264
    265        /**
    266         * Helper method for accessing the element of the specified node.
    267         *
    268         * @param node the node
    269         * @param refHandler the {@code ReferenceNodeHandler}
    270         * @return the element of this node
    271         */
    272        private Element getElement(final ImmutableNode node, final ReferenceNodeHandler refHandler) {
    273            final Element elementNew = newElements.get(node);
    274            if (elementNew != null) {
    275                return elementNew;
    276            }
    277
    278            // special treatment for root node of the hierarchy
    279            final Object reference = refHandler.getReference(node);
    280            final Node element;
    281            if (reference instanceof XMLDocumentHelper) {
    282                element = ((XMLDocumentHelper) reference).getDocument().getDocumentElement();
    283            } else if (reference instanceof XMLListReference) {
    284                element = ((XMLListReference) reference).getElement();
    285            } else {
    286                element = (Node) reference;
    287            }
    288            return element != null ? (Element) elementMapping.get(element) : document.getDocumentElement();
    289        }
    290
    291        /**
    292         * Updates the current XML document regarding removed nodes. The elements associated with removed nodes are removed from
    293         * the document.
    294         *
    295         * @param refHandler the {@code ReferenceNodeHandler}
    296         */
    297        public void handleRemovedNodes(final ReferenceNodeHandler refHandler) {
    298            refHandler.removedReferences().stream().filter(Node.class::isInstance).forEach(ref -> removeReference(elementMapping.get(ref)));
    299        }
    300
    301        /**
    302         * {@inheritDoc} This implementation ensures that the correct XML element is created and inserted between the given
    303         * siblings.
    304         */
    305        @Override
    306        protected void insert(final ImmutableNode newNode, final ImmutableNode parent, final ImmutableNode sibling1, final ImmutableNode sibling2,
    307            final ReferenceNodeHandler refHandler) {
    308            if (XMLListReference.isListNode(newNode, refHandler)) {
    309                return;
    310            }
    311
    312            final Element elem = document.createElement(newNode.getNodeName());
    313            newElements.put(newNode, elem);
    314            updateAttributes(newNode, elem);
    315            if (newNode.getValue() != null) {
    316                final String txt = String.valueOf(listDelimiterHandler.escape(newNode.getValue(), ListDelimiterHandler.NOOP_TRANSFORMER));
    317                elem.appendChild(document.createTextNode(txt));
    318            }
    319            if (sibling2 == null) {
    320                getElement(parent, refHandler).appendChild(elem);
    321            } else if (sibling1 != null) {
    322                getElement(parent, refHandler).insertBefore(elem, getElement(sibling1, refHandler).getNextSibling());
    323            } else {
    324                getElement(parent, refHandler).insertBefore(elem, getElement(parent, refHandler).getFirstChild());
    325            }
    326        }
    327
    328        /**
    329         * Processes the specified document, updates element values, and adds new nodes to the hierarchy.
    330         *
    331         * @param refHandler the {@code ReferenceNodeHandler}
    332         */
    333        public void processDocument(final ReferenceNodeHandler refHandler) {
    334            updateAttributes(refHandler.getRootNode(), document.getDocumentElement());
    335            NodeTreeWalker.INSTANCE.walkDFS(refHandler.getRootNode(), this, refHandler);
    336        }
    337
    338        /**
    339         * Updates the associated XML elements when a node is removed.
    340         *
    341         * @param element the element to be removed
    342         */
    343        private void removeReference(final Node element) {
    344            final Node parentElem = element.getParentNode();
    345            if (parentElem != null) {
    346                parentElem.removeChild(element);
    347            }
    348        }
    349
    350        /**
    351         * {@inheritDoc} This implementation determines the XML element associated with the given node. Then this element's
    352         * value and attributes are set accordingly.
    353         */
    354        @Override
    355        protected void update(final ImmutableNode node, final Object reference, final ReferenceNodeHandler refHandler) {
    356            if (XMLListReference.isListNode(node, refHandler)) {
    357                if (XMLListReference.isFirstListItem(node, refHandler)) {
    358                    final String value = XMLListReference.listValue(node, refHandler, listDelimiterHandler);
    359                    updateElement(node, refHandler, value);
    360                }
    361            } else {
    362                final Object value = listDelimiterHandler.escape(refHandler.getValue(node), ListDelimiterHandler.NOOP_TRANSFORMER);
    363                updateElement(node, refHandler, value);
    364            }
    365        }
    366
    367        /**
    368         * Updates the node's value if it represents an element node.
    369         *
    370         * @param element the element
    371         * @param value the new value
    372         */
    373        private void updateElement(final Element element, final Object value) {
    374            Text txtNode = findTextNodeForUpdate(element);
    375            if (value == null) {
    376                // remove text
    377                if (txtNode != null) {
    378                    element.removeChild(txtNode);
    379                }
    380            } else {
    381                final String newValue = String.valueOf(value);
    382                if (txtNode == null) {
    383                    txtNode = document.createTextNode(newValue);
    384                    if (element.getFirstChild() != null) {
    385                        element.insertBefore(txtNode, element.getFirstChild());
    386                    } else {
    387                        element.appendChild(txtNode);
    388                    }
    389                } else {
    390                    txtNode.setNodeValue(newValue);
    391                }
    392            }
    393        }
    394
    395        private void updateElement(final ImmutableNode node, final ReferenceNodeHandler refHandler, final Object value) {
    396            final Element element = getElement(node, refHandler);
    397            updateElement(element, value);
    398            updateAttributes(node, element);
    399        }
    400    }
    401
    402    /** Constant for the default indent size. */
    403    static final int DEFAULT_INDENT_SIZE = 2;
    404
    405    /** Constant for output property name used on a transformer to specify the indent amount. */
    406    static final String INDENT_AMOUNT_PROPERTY = "{http://xml.apache.org/xslt}indent-amount";
    407
    408    /** Constant for the default root element name. */
    409    private static final String DEFAULT_ROOT_NAME = "configuration";
    410
    411    /** Constant for the name of the space attribute. */
    412    private static final String ATTR_SPACE = "xml:space";
    413
    414    /** Constant for an internally used space attribute. */
    415    private static final String ATTR_SPACE_INTERNAL = "config-xml:space";
    416
    417    /** Constant for the xml:space value for preserving whitespace. */
    418    private static final String VALUE_PRESERVE = "preserve";
    419
    420    /** Schema Langauge key for the parser */
    421    private static final String JAXP_SCHEMA_LANGUAGE = "http://java.sun.com/xml/jaxp/properties/schemaLanguage";
    422
    423    /** Schema Language for the parser */
    424    private static final String W3C_XML_SCHEMA = "http://www.w3.org/2001/XMLSchema";
    425
    426    /**
    427     * Determines the number of child elements of this given node with the specified node name.
    428     *
    429     * @param parent the parent node
    430     * @param name the name in question
    431     * @return the number of child elements with this name
    432     */
    433    private static int countChildElements(final Node parent, final String name) {
    434        final NodeList childNodes = parent.getChildNodes();
    435        int count = 0;
    436        for (int i = 0; i < childNodes.getLength(); i++) {
    437            final Node item = childNodes.item(i);
    438            if (item instanceof Element && name.equals(((Element) item).getTagName())) {
    439                count++;
    440            }
    441        }
    442        return count;
    443    }
    444
    445    /**
    446     * Determines the value of a configuration node. This method mainly checks whether the text value is to be trimmed or
    447     * not. This is normally defined by the trim flag. However, if the node has children and its content is only whitespace,
    448     * then it makes no sense to store any value; this would only scramble layout when the configuration is saved again.
    449     *
    450     * @param content the text content of this node
    451     * @param hasChildren a flag whether the node has children
    452     * @param trimFlag the trim flag
    453     * @return the value to be stored for this node
    454     */
    455    private static String determineValue(final String content, final boolean hasChildren, final boolean trimFlag) {
    456        final boolean shouldTrim = trimFlag || StringUtils.isBlank(content) && hasChildren;
    457        return shouldTrim ? content.trim() : content;
    458    }
    459
    460    /**
    461     * Checks whether an element defines a complete list. If this is the case, extended list handling can be applied.
    462     *
    463     * @param element the element to be checked
    464     * @return a flag whether this is the only element defining the list
    465     */
    466    private static boolean isSingleElementList(final Element element) {
    467        final Node parentNode = element.getParentNode();
    468        return countChildElements(parentNode, element.getTagName()) == 1;
    469    }
    470
    471    /**
    472     * Helper method for initializing the attributes of a configuration node from the given XML element.
    473     *
    474     * @param element the current XML element
    475     * @return a map with all attribute values extracted for the current node
    476     */
    477    private static Map<String, String> processAttributes(final Element element) {
    478        final NamedNodeMap attributes = element.getAttributes();
    479        final Map<String, String> attrmap = new HashMap<>();
    480
    481        for (int i = 0; i < attributes.getLength(); ++i) {
    482            final Node w3cNode = attributes.item(i);
    483            if (w3cNode instanceof Attr) {
    484                final Attr attr = (Attr) w3cNode;
    485                attrmap.put(attr.getName(), attr.getValue());
    486            }
    487        }
    488
    489        return attrmap;
    490    }
    491
    492    /**
    493     * Checks whether the content of the current XML element should be trimmed. This method checks whether a
    494     * {@code xml:space} attribute is present and evaluates its value. See
    495     * <a href="http://www.w3.org/TR/REC-xml/#sec-white-space"> http://www.w3.org/TR/REC-xml/#sec-white-space</a> for more
    496     * details.
    497     *
    498     * @param element the current XML element
    499     * @param currentTrim the current trim flag
    500     * @return a flag whether the content of this element should be trimmed
    501     */
    502    private static boolean shouldTrim(final Element element, final boolean currentTrim) {
    503        final Attr attr = element.getAttributeNode(ATTR_SPACE);
    504
    505        if (attr == null) {
    506            return currentTrim;
    507        }
    508        return !VALUE_PRESERVE.equals(attr.getValue());
    509    }
    510
    511    /** Stores the name of the root element. */
    512    private String rootElementName;
    513
    514    /** Stores the public ID from the DOCTYPE. */
    515    private String publicID;
    516
    517    /** Stores the system ID from the DOCTYPE. */
    518    private String systemID;
    519
    520    /** Stores the document builder that should be used for loading. */
    521    private DocumentBuilder documentBuilder;
    522
    523    /** Stores a flag whether DTD or Schema validation should be performed. */
    524    private boolean validating;
    525
    526    /** Stores a flag whether DTD or Schema validation is used */
    527    private boolean schemaValidation;
    528
    529    /** The EntityResolver to use */
    530    private EntityResolver entityResolver = new DefaultEntityResolver();
    531
    532    /** The current file locator. */
    533    private FileLocator locator;
    534
    535    /**
    536     * Creates a new instance of {@code XMLConfiguration}.
    537     */
    538    public XMLConfiguration() {
    539        initLogger(new ConfigurationLogger(XMLConfiguration.class));
    540    }
    541
    542    /**
    543     * Creates a new instance of {@code XMLConfiguration} and copies the content of the passed in configuration into this
    544     * object. Note that only the data of the passed in configuration will be copied. If, for instance, the other
    545     * configuration is a {@code XMLConfiguration}, too, things like comments or processing instructions will be lost.
    546     *
    547     * @param c the configuration to copy
    548     * @since 1.4
    549     */
    550    public XMLConfiguration(final HierarchicalConfiguration<ImmutableNode> c) {
    551        super(c);
    552        rootElementName = c != null ? c.getRootElementName() : null;
    553        initLogger(new ConfigurationLogger(XMLConfiguration.class));
    554    }
    555
    556    /**
    557     * Helper method for building the internal storage hierarchy. The XML elements are transformed into node objects.
    558     *
    559     * @param node a builder for the current node
    560     * @param refValue stores the text value of the element
    561     * @param element the current XML element
    562     * @param elemRefs a map for assigning references objects to nodes; can be <strong>null</strong>, then reference objects are
    563     *        irrelevant
    564     * @param trim a flag whether the text content of elements should be trimmed; this controls the whitespace handling
    565     * @param level the current level in the hierarchy
    566     * @return a map with all attribute values extracted for the current node; this map also contains the value of the trim
    567     *         flag for this node under the key {@value #ATTR_SPACE}
    568     */
    569    private Map<String, String> constructHierarchy(final ImmutableNode.Builder node, final MutableObject<String> refValue, final Element element,
    570        final Map<ImmutableNode, Object> elemRefs, final boolean trim, final int level) {
    571        final boolean trimFlag = shouldTrim(element, trim);
    572        final Map<String, String> attributes = processAttributes(element);
    573        attributes.put(ATTR_SPACE_INTERNAL, String.valueOf(trimFlag));
    574        final StringBuilder buffer = new StringBuilder();
    575        final NodeList list = element.getChildNodes();
    576        boolean hasChildren = false;
    577
    578        for (int i = 0; i < list.getLength(); i++) {
    579            final Node w3cNode = list.item(i);
    580            if (w3cNode instanceof Element) {
    581                final Element child = (Element) w3cNode;
    582                final ImmutableNode.Builder childNode = new ImmutableNode.Builder();
    583                childNode.name(child.getTagName());
    584                final MutableObject<String> refChildValue = new MutableObject<>();
    585                final Map<String, String> attrmap = constructHierarchy(childNode, refChildValue, child, elemRefs, trimFlag, level + 1);
    586                final boolean childTrim = Boolean.parseBoolean(attrmap.remove(ATTR_SPACE_INTERNAL));
    587                childNode.addAttributes(attrmap);
    588                final ImmutableNode newChild = createChildNodeWithValue(node, childNode, child, refChildValue.getValue(), childTrim, attrmap, elemRefs);
    589                if (elemRefs != null && !elemRefs.containsKey(newChild)) {
    590                    elemRefs.put(newChild, child);
    591                }
    592                hasChildren = true;
    593            } else if (w3cNode instanceof Text) {
    594                final Text data = (Text) w3cNode;
    595                buffer.append(data.getData());
    596            }
    597        }
    598
    599        boolean childrenFlag = false;
    600        if (hasChildren || trimFlag) {
    601            childrenFlag = hasChildren || attributes.size() > 1;
    602        }
    603        final String text = determineValue(buffer.toString(), childrenFlag, trimFlag);
    604        if (!text.isEmpty() || !childrenFlag && level != 0) {
    605            refValue.setValue(text);
    606        }
    607        return attributes;
    608    }
    609
    610    /**
    611     * Creates a new child node, assigns its value, and adds it to its parent. This method also deals with elements whose
    612     * value is a list. In this case multiple child elements must be added. The return value is the first child node which
    613     * was added.
    614     *
    615     * @param parent the builder for the parent element
    616     * @param child the builder for the child element
    617     * @param elem the associated XML element
    618     * @param value the value of the child element
    619     * @param trim flag whether texts of elements should be trimmed
    620     * @param attrmap a map with the attributes of the current node
    621     * @param elemRefs a map for assigning references objects to nodes; can be <strong>null</strong>, then reference objects are
    622     *        irrelevant
    623     * @return the first child node added to the parent
    624     */
    625    private ImmutableNode createChildNodeWithValue(final ImmutableNode.Builder parent, final ImmutableNode.Builder child, final Element elem,
    626        final String value, final boolean trim, final Map<String, String> attrmap, final Map<ImmutableNode, Object> elemRefs) {
    627        final ImmutableNode addedChildNode;
    628        final Collection<String> values;
    629
    630        if (value != null) {
    631            values = getListDelimiterHandler().split(value, trim);
    632        } else {
    633            values = Collections.emptyList();
    634        }
    635
    636        if (values.size() > 1) {
    637            final Map<ImmutableNode, Object> refs = isSingleElementList(elem) ? elemRefs : null;
    638            final Iterator<String> it = values.iterator();
    639            // Create new node for the original child's first value
    640            child.value(it.next());
    641            addedChildNode = child.create();
    642            parent.addChild(addedChildNode);
    643            XMLListReference.assignListReference(refs, addedChildNode, elem);
    644
    645            // add multiple new children
    646            while (it.hasNext()) {
    647                final ImmutableNode.Builder c = new ImmutableNode.Builder();
    648                c.name(addedChildNode.getNodeName());
    649                c.value(it.next());
    650                c.addAttributes(attrmap);
    651                final ImmutableNode newChild = c.create();
    652                parent.addChild(newChild);
    653                XMLListReference.assignListReference(refs, newChild, null);
    654            }
    655        } else {
    656            if (values.size() == 1) {
    657                // we will have to replace the value because it might
    658                // contain escaped delimiters
    659                child.value(values.iterator().next());
    660            }
    661            addedChildNode = child.create();
    662            parent.addChild(addedChildNode);
    663        }
    664
    665        return addedChildNode;
    666    }
    667
    668    /**
    669     * Creates a DOM document from the internal tree of configuration nodes.
    670     *
    671     * @return the new document
    672     * @throws ConfigurationException if an error occurs
    673     */
    674    private Document createDocument() throws ConfigurationException {
    675        final ReferenceNodeHandler handler = getReferenceHandler();
    676        final XMLDocumentHelper docHelper = (XMLDocumentHelper) handler.getReference(handler.getRootNode());
    677        final XMLDocumentHelper newHelper = docHelper == null ? XMLDocumentHelper.forNewDocument(getRootElementName()) : docHelper.createCopy();
    678
    679        final XMLBuilderVisitor builder = new XMLBuilderVisitor(newHelper, getListDelimiterHandler());
    680        builder.handleRemovedNodes(handler);
    681        builder.processDocument(handler);
    682        initRootElementText(newHelper.getDocument(), getModel().getNodeHandler().getRootNode().getValue());
    683        return newHelper.getDocument();
    684    }
    685
    686    /**
    687     * Creates the {@code DocumentBuilder} to be used for loading files. This implementation checks whether a specific
    688     * {@code DocumentBuilder} has been set. If this is the case, this one is used. Otherwise a default builder is created.
    689     * Depending on the value of the validating flag this builder will be a validating or a non validating
    690     * {@code DocumentBuilder}.
    691     *
    692     * @return the {@code DocumentBuilder} for loading configuration files
    693     * @throws ParserConfigurationException if an error occurs
    694     * @since 1.2
    695     */
    696    protected DocumentBuilder createDocumentBuilder() throws ParserConfigurationException {
    697        if (getDocumentBuilder() != null) {
    698            return getDocumentBuilder();
    699        }
    700        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    701        if (isValidating()) {
    702            factory.setValidating(true);
    703            if (isSchemaValidation()) {
    704                factory.setNamespaceAware(true);
    705                factory.setAttribute(JAXP_SCHEMA_LANGUAGE, W3C_XML_SCHEMA);
    706            }
    707        }
    708
    709        final DocumentBuilder result = factory.newDocumentBuilder();
    710        result.setEntityResolver(this.entityResolver);
    711
    712        if (isValidating()) {
    713            // register an error handler which detects validation errors
    714            result.setErrorHandler(new DefaultHandler() {
    715                @Override
    716                public void error(final SAXParseException ex) throws SAXException {
    717                    throw ex;
    718                }
    719            });
    720        }
    721        return result;
    722    }
    723
    724    /**
    725     * Creates and initializes the transformer used for save operations. This base implementation initializes all of the
    726     * default settings like indentation mode and the DOCTYPE. Derived classes may overload this method if they have
    727     * specific needs.
    728     *
    729     * @return the transformer to use for a save operation
    730     * @throws ConfigurationException if an error occurs
    731     * @since 1.3
    732     */
    733    protected Transformer createTransformer() throws ConfigurationException {
    734        final Transformer transformer = XMLDocumentHelper.createTransformer();
    735
    736        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
    737        transformer.setOutputProperty(INDENT_AMOUNT_PROPERTY, Integer.toString(DEFAULT_INDENT_SIZE));
    738        if (locator != null && locator.getEncoding() != null) {
    739            transformer.setOutputProperty(OutputKeys.ENCODING, locator.getEncoding());
    740        }
    741        if (publicID != null) {
    742            transformer.setOutputProperty(OutputKeys.DOCTYPE_PUBLIC, publicID);
    743        }
    744        if (systemID != null) {
    745            transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, systemID);
    746        }
    747
    748        return transformer;
    749    }
    750
    751    /**
    752     * Gets the XML document this configuration was loaded from. The return value is <strong>null</strong> if this configuration
    753     * was not loaded from a XML document.
    754     *
    755     * @return the XML document this configuration was loaded from
    756     */
    757    public Document getDocument() {
    758        final XMLDocumentHelper docHelper = getDocumentHelper();
    759        return docHelper != null ? docHelper.getDocument() : null;
    760    }
    761
    762    /**
    763     * Gets the {@code DocumentBuilder} object that is used for loading documents. If no specific builder has been set,
    764     * this method returns <strong>null</strong>.
    765     *
    766     * @return the {@code DocumentBuilder} for loading new documents
    767     * @since 1.2
    768     */
    769    public DocumentBuilder getDocumentBuilder() {
    770        return documentBuilder;
    771    }
    772
    773    /**
    774     * Gets the helper object for managing the underlying document.
    775     *
    776     * @return the {@code XMLDocumentHelper}
    777     */
    778    private XMLDocumentHelper getDocumentHelper() {
    779        final ReferenceNodeHandler handler = getReferenceHandler();
    780        return (XMLDocumentHelper) handler.getReference(handler.getRootNode());
    781    }
    782
    783    /**
    784     * Gets the EntityResolver.
    785     *
    786     * @return The EntityResolver.
    787     * @since 1.7
    788     */
    789    public EntityResolver getEntityResolver() {
    790        return this.entityResolver;
    791    }
    792
    793    /**
    794     * Gets the public ID of the DOCTYPE declaration from the loaded XML document. This is <strong>null</strong> if no document has
    795     * been loaded yet or if the document does not contain a DOCTYPE declaration with a public ID.
    796     *
    797     * @return the public ID
    798     * @since 1.3
    799     */
    800    public String getPublicID() {
    801        return syncReadValue(publicID, false);
    802    }
    803
    804    /**
    805     * Gets the extended node handler with support for references.
    806     *
    807     * @return the {@code ReferenceNodeHandler}
    808     */
    809    private ReferenceNodeHandler getReferenceHandler() {
    810        return getSubConfigurationParentModel().getReferenceNodeHandler();
    811    }
    812
    813    /**
    814     * Gets the name of the root element. If this configuration was loaded from a XML document, the name of this
    815     * document's root element is returned. Otherwise it is possible to set a name for the root element that will be used
    816     * when this configuration is stored.
    817     *
    818     * @return the name of the root element
    819     */
    820    @Override
    821    protected String getRootElementNameInternal() {
    822        final Document doc = getDocument();
    823        if (doc == null) {
    824            return rootElementName == null ? DEFAULT_ROOT_NAME : rootElementName;
    825        }
    826        return doc.getDocumentElement().getNodeName();
    827    }
    828
    829    /**
    830     * Gets the system ID of the DOCTYPE declaration from the loaded XML document. This is <strong>null</strong> if no document has
    831     * been loaded yet or if the document does not contain a DOCTYPE declaration with a system ID.
    832     *
    833     * @return the system ID
    834     * @since 1.3
    835     */
    836    public String getSystemID() {
    837        return syncReadValue(systemID, false);
    838    }
    839
    840    /**
    841     * {@inheritDoc} Stores the passed in locator for the upcoming IO operation.
    842     */
    843    @Override
    844    public void initFileLocator(final FileLocator loc) {
    845        locator = loc;
    846    }
    847
    848    /**
    849     * Initializes this configuration from an XML document.
    850     *
    851     * @param docHelper the helper object with the document to be parsed
    852     * @param elemRefs a flag whether references to the XML elements should be set
    853     */
    854    private void initProperties(final XMLDocumentHelper docHelper, final boolean elemRefs) {
    855        final Document document = docHelper.getDocument();
    856        setPublicID(docHelper.getSourcePublicID());
    857        setSystemID(docHelper.getSourceSystemID());
    858
    859        final ImmutableNode.Builder rootBuilder = new ImmutableNode.Builder();
    860        final MutableObject<String> rootValue = new MutableObject<>();
    861        final Map<ImmutableNode, Object> elemRefMap = elemRefs ? new HashMap<>() : null;
    862        final Map<String, String> attributes = constructHierarchy(rootBuilder, rootValue, document.getDocumentElement(), elemRefMap, true, 0);
    863        attributes.remove(ATTR_SPACE_INTERNAL);
    864        final ImmutableNode top = rootBuilder.value(rootValue.getValue()).addAttributes(attributes).create();
    865        getSubConfigurationParentModel().mergeRoot(top, document.getDocumentElement().getTagName(), elemRefMap, elemRefs ? docHelper : null, this);
    866    }
    867
    868    /**
    869     * Sets the text of the root element of a newly created XML Document.
    870     *
    871     * @param doc the document
    872     * @param value the new text to be set
    873     */
    874    private void initRootElementText(final Document doc, final Object value) {
    875        final Element elem = doc.getDocumentElement();
    876        final NodeList children = elem.getChildNodes();
    877
    878        // Remove all existing text nodes
    879        for (int i = 0; i < children.getLength(); i++) {
    880            final Node nd = children.item(i);
    881            if (nd.getNodeType() == Node.TEXT_NODE) {
    882                elem.removeChild(nd);
    883            }
    884        }
    885
    886        if (value != null) {
    887            // Add a new text node
    888            elem.appendChild(doc.createTextNode(String.valueOf(value)));
    889        }
    890    }
    891
    892    /**
    893     * Returns the value of the schemaValidation flag.
    894     *
    895     * @return the schemaValidation flag
    896     * @since 1.7
    897     */
    898    public boolean isSchemaValidation() {
    899        return schemaValidation;
    900    }
    901
    902    /**
    903     * Returns the value of the validating flag.
    904     *
    905     * @return the validating flag
    906     * @since 1.2
    907     */
    908    public boolean isValidating() {
    909        return validating;
    910    }
    911
    912    /**
    913     * Loads a configuration file from the specified input source.
    914     *
    915     * @param source the input source
    916     * @throws ConfigurationException if an error occurs
    917     */
    918    private void load(final InputSource source) throws ConfigurationException {
    919        if (locator == null) {
    920            throw new ConfigurationException(
    921                "Load operation not properly " + "initialized! Do not call read(InputStream) directly," + " but use a FileHandler to load a configuration.");
    922        }
    923
    924        try {
    925            final URL sourceURL = locator.getSourceURL();
    926            if (sourceURL != null) {
    927                source.setSystemId(sourceURL.toString());
    928            }
    929
    930            final DocumentBuilder builder = createDocumentBuilder();
    931            final Document newDocument = builder.parse(source);
    932            final Document oldDocument = getDocument();
    933            initProperties(XMLDocumentHelper.forSourceDocument(newDocument), oldDocument == null);
    934        } catch (final SAXParseException spe) {
    935            throw new ConfigurationException("Error parsing " + source.getSystemId(), spe);
    936        } catch (final Exception e) {
    937            getLogger().debug("Unable to load the configuration: " + e);
    938            throw new ConfigurationException("Unable to load the configuration", e);
    939        }
    940    }
    941
    942    /**
    943     * Loads the configuration from the given input stream. This is analogous to {@link #read(Reader)}, but data is read
    944     * from a stream. Note that this method will be called most time when reading an XML configuration source. By reading
    945     * XML documents directly from an input stream, the file's encoding can be correctly dealt with.
    946     *
    947     * @param in the input stream
    948     * @throws ConfigurationException if an error occurs
    949     * @throws IOException if an IO error occurs
    950     */
    951    @Override
    952    public void read(final InputStream in) throws ConfigurationException, IOException {
    953        load(new InputSource(in));
    954    }
    955
    956    /**
    957     * Loads the configuration from the given reader. Note that the {@code clear()} method is not called, so the properties
    958     * contained in the loaded file will be added to the current set of properties.
    959     *
    960     * @param in the reader
    961     * @throws ConfigurationException if an error occurs
    962     * @throws IOException if an IO error occurs
    963     */
    964    @Override
    965    public void read(final Reader in) throws ConfigurationException, IOException {
    966        load(new InputSource(in));
    967    }
    968
    969    /**
    970     * Sets the {@code DocumentBuilder} object to be used for loading documents. This method makes it possible to specify
    971     * the exact document builder. So an application can create a builder, configure it for its special needs, and then pass
    972     * it to this method.
    973     *
    974     * @param documentBuilder the document builder to be used; if undefined, a default builder will be used
    975     * @since 1.2
    976     */
    977    public void setDocumentBuilder(final DocumentBuilder documentBuilder) {
    978        this.documentBuilder = documentBuilder;
    979    }
    980
    981    /**
    982     * Sets a new EntityResolver. Setting this will cause RegisterEntityId to have no effect.
    983     *
    984     * @param resolver The EntityResolver to use.
    985     * @since 1.7
    986     */
    987    public void setEntityResolver(final EntityResolver resolver) {
    988        this.entityResolver = resolver;
    989    }
    990
    991    /**
    992     * Sets the public ID of the DOCTYPE declaration. When this configuration is saved, a DOCTYPE declaration will be
    993     * constructed that contains this public ID.
    994     *
    995     * @param publicID the public ID
    996     * @since 1.3
    997     */
    998    public void setPublicID(final String publicID) {
    999        syncWrite(() -> this.publicID = publicID, false);
    1000    }
    1001
    1002    /**
    1003     * Sets the name of the root element. This name is used when this configuration object is stored in an XML file. Note
    1004     * that setting the name of the root element works only if this configuration has been newly created. If the
    1005     * configuration was loaded from an XML file, the name cannot be changed and an {@code UnsupportedOperationException}
    1006     * exception is thrown. Whether this configuration has been loaded from an XML document or not can be found out using
    1007     * the {@code getDocument()} method.
    1008     *
    1009     * @param name the name of the root element
    1010     */
    1011    public void setRootElementName(final String name) {
    1012        beginRead(true);
    1013        try {
    1014            if (getDocument() != null) {
    1015                throw new UnsupportedOperationException("The name of the root element " + "cannot be changed when loaded from an XML document!");
    1016            }
    1017            rootElementName = name;
    1018        } finally {
    1019            endRead();
    1020        }
    1021    }
    1022
    1023    /**
    1024     * Sets the value of the schemaValidation flag. This flag determines whether DTD or Schema validation should be used.
    1025     * This flag is evaluated only if no custom {@code DocumentBuilder} was set. If set to true the XML document must
    1026     * contain a schemaLocation definition that provides resolvable hints to the required schemas.
    1027     *
    1028     * @param schemaValidation the validating flag
    1029     * @since 1.7
    1030     */
    1031    public void setSchemaValidation(final boolean schemaValidation) {
    1032        this.schemaValidation = schemaValidation;
    1033        if (schemaValidation) {
    1034            this.validating = true;
    1035        }
    1036    }
    1037
    1038    /**
    1039     * Sets the system ID of the DOCTYPE declaration. When this configuration is saved, a DOCTYPE declaration will be
    1040     * constructed that contains this system ID.
    1041     *
    1042     * @param systemID the system ID
    1043     * @since 1.3
    1044     */
    1045    public void setSystemID(final String systemID) {
    1046        syncWrite(() -> this.systemID = systemID, false);
    1047    }
    1048
    1049    /**
    1050     * Sets the value of the validating flag. This flag determines whether DTD/Schema validation should be performed when
    1051     * loading XML documents. This flag is evaluated only if no custom {@code DocumentBuilder} was set.
    1052     *
    1053     * @param validating the validating flag
    1054     * @since 1.2
    1055     */
    1056    public void setValidating(final boolean validating) {
    1057        if (!schemaValidation) {
    1058            this.validating = validating;
    1059        }
    1060    }
    1061
    1062    /**
    1063     * Validate the document against the Schema.
    1064     *
    1065     * @throws ConfigurationException if the validation fails.
    1066     */
    1067    public void validate() throws ConfigurationException {
    1068        syncWrite(() -> {
    1069            try {
    1070                final StringWriter writer = new StringWriter();
    1071                final Result result = new StreamResult(writer);
    1072                XMLDocumentHelper.transform(createTransformer(), new DOMSource(createDocument()), result);
    1073                final Reader reader = new StringReader(writer.getBuffer().toString());
    1074                createDocumentBuilder().parse(new InputSource(reader));
    1075            } catch (final SAXException | IOException | ParserConfigurationException pce) {
    1076                throw new ConfigurationException("Validation failed", pce);
    1077            }
    1078        }, false);
    1079    }
    1080
    1081    /**
    1082     * Saves the configuration to the specified writer.
    1083     *
    1084     * @param writer the writer used to save the configuration
    1085     * @throws ConfigurationException if an error occurs
    1086     * @throws IOException if an IO error occurs
    1087     */
    1088    @Override
    1089    public void write(final Writer writer) throws ConfigurationException, IOException {
    1090        write(writer, createTransformer());
    1091    }
    1092
    1093    /**
    1094     * Saves the configuration to the specified writer.
    1095     *
    1096     * @param writer the writer used to save the configuration.
    1097     * @param transformer How to transform this configuration.
    1098     * @throws ConfigurationException if an error occurs.
    1099     * @since 2.7.0
    1100     */
    1101    public void write(final Writer writer, final Transformer transformer) throws ConfigurationException {
    1102        final Source source = new DOMSource(createDocument());
    1103        final Result result = new StreamResult(writer);
    1104        XMLDocumentHelper.transform(transformer, source, result);
    1105    }
    1106}