XMLDocumentHelper.java
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* 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;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.Result;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMResult;
import javax.xml.transform.dom.DOMSource;
import org.apache.commons.configuration2.ex.ConfigurationException;
import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
/**
* <p>
* An internally used helper class for dealing with XML documents.
* </p>
* <p>
* This class is used by {@link XMLConfiguration}. It provides some basic functionality for processing DOM documents and
* dealing with elements. The main idea is that an instance holds the XML document associated with a XML configuration
* object. When the configuration is to be saved the document has to be manipulated according to the changes made on the
* configuration. To ensure that this is possible even under concurrent access, a new temporary instance is created as a
* copy of the original instance. Then, on this copy, the changes of the configuration are applied. The resulting
* document can then be serialized.
* </p>
* <p>
* Nodes of an {@code XMLConfiguration} that was read from a file are associated with the XML elements they represent.
* In order to apply changes on the copied document, it is necessary to establish a mapping between the elements of the
* old document and the elements of the copied document. This is also handled by this class.
* </p>
*
* @since 2.0
*/
final class XMLDocumentHelper {
/**
* Creates a copy of the specified document.
*
* @param doc the {@code Document}
* @return the copy of this document
* @throws ConfigurationException if an error occurs
*/
private static Document copyDocument(final Document doc) throws ConfigurationException {
final Transformer transformer = createTransformer();
final DOMSource source = new DOMSource(doc);
final DOMResult result = new DOMResult();
transform(transformer, source, result);
return (Document) result.getNode();
}
/**
* Creates a new {@code DocumentBuilder} using the specified factory. Exceptions are rethrown as
* {@code ConfigurationException} exceptions.
*
* @param factory the {@code DocumentBuilderFactory}
* @return the newly created {@code DocumentBuilder}
* @throws ConfigurationException if an error occurs
*/
static DocumentBuilder createDocumentBuilder(final DocumentBuilderFactory factory) throws ConfigurationException {
try {
return factory.newDocumentBuilder();
} catch (final ParserConfigurationException pcex) {
throw new ConfigurationException(pcex);
}
}
/**
* Creates a new {@code DocumentBuilderFactory} instance.
*
* @return the new factory object
*/
private static DocumentBuilderFactory createDocumentBuilderFactory() {
return DocumentBuilderFactory.newInstance();
}
/**
* Creates the element mapping for the specified documents. For each node in the source document an entry is created
* pointing to the corresponding node in the destination object.
*
* @param doc1 the source document
* @param doc2 the destination document
* @return the element mapping
*/
private static Map<Node, Node> createElementMapping(final Document doc1, final Document doc2) {
final Map<Node, Node> mapping = new HashMap<>();
createElementMappingForNodes(doc1.getDocumentElement(), doc2.getDocumentElement(), mapping);
return mapping;
}
/**
* Creates the element mapping for the specified nodes and all their child nodes.
*
* @param n1 node 1
* @param n2 node 2
* @param mapping the mapping to be filled
*/
private static void createElementMappingForNodes(final Node n1, final Node n2, final Map<Node, Node> mapping) {
mapping.put(n1, n2);
final NodeList childNodes1 = n1.getChildNodes();
final NodeList childNodes2 = n2.getChildNodes();
final int count = Math.min(childNodes1.getLength(), childNodes2.getLength());
for (int i = 0; i < count; i++) {
createElementMappingForNodes(childNodes1.item(i), childNodes2.item(i), mapping);
}
}
/**
* Creates a new {@code Transformer} object. No initializations are performed on the new instance.
*
* @return the new {@code Transformer}
* @throws ConfigurationException if the {@code Transformer} could not be created
*/
public static Transformer createTransformer() throws ConfigurationException {
return createTransformer(createTransformerFactory());
}
/**
* Creates a {@code Transformer} using the specified factory.
*
* @param factory the {@code TransformerFactory}
* @return the newly created {@code Transformer}
* @throws ConfigurationException if an error occurs
*/
static Transformer createTransformer(final TransformerFactory factory) throws ConfigurationException {
try {
return factory.newTransformer();
} catch (final TransformerConfigurationException tex) {
throw new ConfigurationException(tex);
}
}
/**
* Creates a new {@code TransformerFactory}.
*
* @return the {@code TransformerFactory}
*/
static TransformerFactory createTransformerFactory() {
return TransformerFactory.newInstance();
}
/**
* Creates an empty element mapping.
*
* @return the empty mapping
*/
private static Map<Node, Node> emptyElementMapping() {
return Collections.emptyMap();
}
/**
* Creates a new instance of {@code XMLDocumentHelper} and initializes it with a newly created, empty {@code Document}.
* The new document has a root element with the given element name. This element has no further child nodes.
*
* @param rootElementName the name of the root element
* @return the newly created instance
* @throws ConfigurationException if an error occurs when creating the document
*/
public static XMLDocumentHelper forNewDocument(final String rootElementName) throws ConfigurationException {
final Document doc = createDocumentBuilder(createDocumentBuilderFactory()).newDocument();
final Element rootElem = doc.createElement(rootElementName);
doc.appendChild(rootElem);
return new XMLDocumentHelper(doc, emptyElementMapping(), null, null);
}
/**
* Creates a new instance of {@code XMLDocumentHelper} and initializes it with a source document. This is a document
* created from a configuration file. It is kept in memory so that the configuration can be saved with the same format.
* Note that already a copy of this document is created. This is done for the following reasons:
* <ul>
* <li>It is a defensive copy.</li>
* <li>An identity transformation on a document may change certain nodes, e.g. CDATA sections. When later on again
* copies of this document are created it has to be ensured that these copies have the same structure than the original
* document stored in this instance.</li>
* </ul>
*
* @param srcDoc the source document
* @return the newly created instance
* @throws ConfigurationException if an error occurs
*/
public static XMLDocumentHelper forSourceDocument(final Document srcDoc) throws ConfigurationException {
final String pubID;
final String sysID;
if (srcDoc.getDoctype() != null) {
pubID = srcDoc.getDoctype().getPublicId();
sysID = srcDoc.getDoctype().getSystemId();
} else {
pubID = null;
sysID = null;
}
return new XMLDocumentHelper(copyDocument(srcDoc), emptyElementMapping(), pubID, sysID);
}
/**
* Performs an XSL transformation on the passed in operands. All possible exceptions are caught and redirected as
* {@code ConfigurationException} exceptions.
*
* @param transformer the transformer
* @param source the source
* @param result the result
* @throws ConfigurationException if an error occurs
*/
public static void transform(final Transformer transformer, final Source source, final Result result) throws ConfigurationException {
try {
transformer.transform(source, result);
} catch (final TransformerException tex) {
throw new ConfigurationException(tex);
}
}
/** Stores the document managed by this instance. */
private final Document document;
/** The element mapping to the source document. */
private final Map<Node, Node> elementMapping;
/** Stores the public ID of the source document. */
private final String sourcePublicID;
/** Stores the system ID of the source document. */
private final String sourceSystemID;
/**
* Creates a new instance of {@code XMLDocumentHelper} and initializes it with the given XML document. Note: This
* constructor is package private only for testing purposes. Instances should be created using the static factory
* methods.
*
* @param doc the {@code Document}
* @param elemMap the element mapping
* @param pubID the public ID of the source document
* @param sysID the system ID of the source document
*/
XMLDocumentHelper(final Document doc, final Map<Node, Node> elemMap, final String pubID, final String sysID) {
document = doc;
elementMapping = elemMap;
sourcePublicID = pubID;
sourceSystemID = sysID;
}
/**
* Creates a copy of this object. This copy contains a copy of the document and an element mapping which allows mapping
* elements from the source document to elements of the copied document.
*
* @return the copy
* @throws ConfigurationException if an error occurs
*/
public XMLDocumentHelper createCopy() throws ConfigurationException {
final Document docCopy = copyDocument(getDocument());
return new XMLDocumentHelper(docCopy, createElementMapping(getDocument(), docCopy), getSourcePublicID(), getSourceSystemID());
}
/**
* Gets the {@code Document} managed by this helper.
*
* @return the wrapped {@code Document}
*/
public Document getDocument() {
return document;
}
/**
* Gets the element mapping to the source document. This map can be used to obtain elements in the managed document
* which correspond to elements in the source document. If this instance has not been created from a source document,
* the mapping is empty.
*
* @return the element mapping to the source document
*/
public Map<Node, Node> getElementMapping() {
return elementMapping;
}
/**
* Gets the public ID of the source document.
*
* @return the public ID of the source document
*/
public String getSourcePublicID() {
return sourcePublicID;
}
/**
* Gets the system ID of the source document.
*
* @return the system ID of the source document
*/
public String getSourceSystemID() {
return sourceSystemID;
}
}