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package org.scijava.util;

import java.io.ByteArrayInputStream;

import java.io.ByteArrayOutputStream;

import java.io.File;

import java.io.IOException;

import java.io.InputStream;

import java.io.PrintStream;

import java.io.StringWriter;

import java.net.URL;

import java.util.ArrayList;

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.TransformerException;

import javax.xml.transform.TransformerFactory;

import javax.xml.transform.dom.DOMSource;

import javax.xml.transform.stream.StreamResult;

import javax.xml.xpath.XPath;

import javax.xml.xpath.XPathConstants;

import javax.xml.xpath.XPathExpressionException;

import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.Node;

import org.w3c.dom.NodeList;

import org.xml.sax.SAXException;

/**

* Helper class for working with XML documents.

*

* @author Curtis Rueden

*/

public class XML {

/** Path to the XML document (e.g., a file or URL). */

private final String path;

/** The parsed XML DOM. */

private final Document doc;

/** XPath evaluation mechanism. */

private final XPath xpath;

private final boolean debug =

"debug".equals(System.getProperty("scijava.log.level"));

/** Parses XML from the given file. */

public XML(final File file) throws ParserConfigurationException,

SAXException, IOException

{

this(file.getAbsolutePath(), loadXML(file));

}

/** Parses XML from the given URL. */

public XML(final URL url) throws ParserConfigurationException,

SAXException, IOException

{

this(url.getPath(), loadXML(url));

}

/** Parses XML from the given input stream. */

public XML(final InputStream in) throws ParserConfigurationException,

SAXException, IOException

{

this(null, loadXML(in));

}

/** Parses XML from the given string. */

public XML(final String s) throws ParserConfigurationException,

SAXException, IOException

{

this(null, loadXML(s));

}

/** Creates an XML object for an existing document. */

public XML(final Document doc) {

this(null, doc);

}

/** Creates an XML object for an existing document. */

public XML(final String path, final Document doc) {

this.path = path;

this.doc = doc;

// Protect against class skew: some projects find it funny to ship outdated

// xalan, causing problems due to incompatible xalan/xerces combinations.

//

// We work around that by letting the XPathFactory try with the current

// context class loader, and fall back onto its parent until it succeeds

// (because the XPathFactory will ask the context class loader to find the

// configured services, including the

// com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl).

if (debug) {

System.err.println(Types.location(XPathFactory.class));

}

XPath xp = null;

final Thread thread = Thread.currentThread();

final ClassLoader contextClassLoader = thread.getContextClassLoader();

try {

ClassLoader loader = contextClassLoader;

while (true) {

try {

xp = XPathFactory.newInstance().newXPath();

try {

// make sure that the current xalan/xerces pair can evaluate

// expressions (i.e. *not* throw NoSuchMethodErrors).

xp.evaluate("//dummy", doc);

} catch (Throwable t) {

if (debug) {

System.err.println("There was a problem with " + xp.getClass() +

" in " + Types.location(xp.getClass()) + ":");

t.printStackTrace();

}

throw new Error(t);

}

break;

}

catch (Error e) {

if (debug) e.printStackTrace();

loader = loader.getParent();

if (loader == null) throw e;

thread.setContextClassLoader(loader);

}

}

xpath = xp;

}

finally {

thread.setContextClassLoader(contextClassLoader);

}

}

// -- XML methods --

/** Gets the path to the XML document, or null if none. */

public String getPath() {

return path;

}

/** Gets the XML's DOM representation. */

public Document getDocument() {

return doc;

}

/** Obtains the CDATA identified by the given XPath expression. */

public String cdata(final String expression) {

final NodeList nodes = xpath(expression);

if (nodes == null || nodes.getLength() == 0) return null;

return cdata(nodes.item(0));

}

/** Obtains the elements identified by the given XPath expression. */

public ArrayList<Element> elements(final String expression) {

return elements(xpath(expression));

}

/** Obtains the nodes identified by the given XPath expression. */

public NodeList xpath(final String expression) {

final Object result;

try {

result = xpath.evaluate(expression, doc, XPathConstants.NODESET);

}

catch (final XPathExpressionException e) {

return null;

}

return (NodeList) result;

}

// -- Object methods --

@Override

public String toString() {

try {

return dumpXML(doc);

}

catch (final TransformerException exc) {

// NB: Return the exception stack trace as the string.

// Although this is a bad idea, I find it somehow hilarious.

final ByteArrayOutputStream out = new ByteArrayOutputStream();

exc.printStackTrace(new PrintStream(out));

return out.toString();

}

}

// -- Utility methods --

/** Gets the CData beneath the given node. */

public static String cdata(final Node item) {

final NodeList children = item.getChildNodes();

if (children == null || children.getLength() == 0) return null;

for (int i = 0; i < children.getLength(); i++) {

final Node child = children.item(i);

if (child.getNodeType() != Node.TEXT_NODE) continue;

return child.getNodeValue();

}

return null;

}

/** Gets the CData beneath the given element's specified child. */

public static String cdata(final Element el, final String child) {

NodeList children = el.getElementsByTagName(child);

if (children == null || children.getLength() == 0) return null;

return cdata(children.item(0));

}

/** Gets the element nodes from the given node list. */

public static ArrayList<Element> elements(final NodeList nodes) {

final ArrayList<Element> elements = new ArrayList<>();

if (nodes != null) {

for (int i=0; i<nodes.getLength(); i++) {

final Node node = nodes.item(i);

if (node instanceof Element) elements.add((Element) node);

}

}

return elements;

}

/** Gets the given element's specified child elements. */

public static ArrayList<Element>

elements(final Element el, final String child)

{

return elements(el.getElementsByTagName(child));

}

// -- Helper methods --

/** Loads an XML document from the given file. */

private static Document loadXML(final File file)

throws ParserConfigurationException, SAXException, IOException

{

return createBuilder().parse(file.getAbsolutePath());

}

/** Loads an XML document from the given URL. */

private static Document loadXML(final URL url)

throws ParserConfigurationException, SAXException, IOException

{

final InputStream in = url.openStream();

final Document document = loadXML(in);

in.close();

return document;

}

/** Loads an XML document from the given input stream. */

protected static Document loadXML(final InputStream in)

throws ParserConfigurationException, SAXException, IOException

{

return createBuilder().parse(in);

}

/** Loads an XML document from the given input stream. */

protected static Document loadXML(final String s)

throws ParserConfigurationException, SAXException, IOException

{

return createBuilder().parse(new ByteArrayInputStream(s.getBytes()));

}

/** Creates an XML document builder. */

private static DocumentBuilder createBuilder()

throws ParserConfigurationException

{

return DocumentBuilderFactory.newInstance().newDocumentBuilder();

}

/** Converts the given DOM to a string. */

private static String dumpXML(final Document doc)

throws TransformerException

{

final Source source = new DOMSource(doc);

final StringWriter stringWriter = new StringWriter();

final Result result = new StreamResult(stringWriter);

final TransformerFactory factory = TransformerFactory.newInstance();

final Transformer transformer = factory.newTransformer();

transformer.transform(source, result);

return stringWriter.getBuffer().toString();

}

}