XmlUtil.java

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.nio.charset.StandardCharsets;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
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.DOMSource;
import javax.xml.transform.stream.StreamResult;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xml.sax.SAXException;

public final class XmlUtil {

    private XmlUtil() {
        // NOOP
    }

    public static void main(String[] args) throws Exception {
        // usage
        final byte[] input = "<root>\n    <node>old &#26408;</node>\n</root>"
                .getBytes(StandardCharsets.US_ASCII);
        final Document doc = documentFromByteArray(input);
        final XPath xpath = createXpath();
        final String old = readString(doc, xpath, "/root/node/text()");
        if ("old \u6728".equals(old)) {
            writeString(doc, xpath, "/root/node/text()", "new \u6728");
        }
        final byte[] output = documentToByteArray(doc);
        //final String nl = System.getProperty("line.separator");
        //assert ("<root>" + nl
        //        + "    <node>new &#26408;</node>" + nl
        //        + "</root>" + nl)
        //        .equals(new String(output, StandardCharsets.US_ASCII));
        System.out.println(new String(output, StandardCharsets.US_ASCII));
    }

    public static Document documentFromByteArray(final byte[] bytes) throws SAXException, IOException, ParserConfigurationException {
        final Document doc = documentFromInputStream(new ByteArrayInputStream(bytes));
        return doc;
    }

    public static Document documentFromInputStream(final InputStream is) throws SAXException, IOException, ParserConfigurationException {
        final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        final DocumentBuilder builder = factory.newDocumentBuilder();
        final Document doc = builder.parse(is);
        doc.getDocumentElement().normalize();
        return doc;
    }

    public static byte[] documentToByteArray(final Document doc) throws TransformerConfigurationException, TransformerException {
        final Source source = new DOMSource(doc);
        final ByteArrayOutputStream out = new ByteArrayOutputStream();
        final Result result = new StreamResult(out);
        final TransformerFactory factory = TransformerFactory.newInstance();
        final Transformer transformer = factory.newTransformer();
        transformer.setOutputProperty(OutputKeys.INDENT, "yes");
        transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");
        transformer.setOutputProperty(OutputKeys.ENCODING, "US-ASCII");
        transformer.setOutputProperty(OutputKeys.METHOD, "xml");
        transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        transformer.transform(source, result);
        return out.toByteArray();
    }

    public static XPath createXpath() {
        final XPathFactory xPathfactory = XPathFactory.newInstance();
        final XPath xpath = xPathfactory.newXPath();
        return xpath;
    }

    public static String readString(final Node node, final XPath xpath, final String xpathExpression) throws XPathExpressionException {
        final XPathExpression expr = xpath.compile(xpathExpression);
        final String s = (String) expr.evaluate(node, XPathConstants.STRING);
        return s;
    }

    public static void writeString(final Node node, final XPath xpath, final String xpathExpression, final String value) throws XPathExpressionException {
        final XPathExpression expr = xpath.compile(xpathExpression);
        final Node n = (Node) expr.evaluate(node, XPathConstants.NODE);
        n.setNodeValue(value);
    }

    public static NodeList findNodes(final Node node, final XPath xpath, final String xpathExpression) throws XPathExpressionException {
        final XPathExpression expr = xpath.compile(xpathExpression);
        final NodeList list = (NodeList) expr.evaluate(node, XPathConstants.NODESET);
        return list;
    }

}