https://jsoup.org/: jsoup is a Java library for working with real-world HTML. It provides a very convenient API for extracting and manipulating data, using the best of DOM, CSS, and jquery-like methods. jsoup implements the WHATWG HTML5 specification, and parses HTML to the same DOM as modern browsers do. (Jonathan Hedley)
  • Jonathan Hedley 
package org.jsoup.helper;

import org.jsoup.internal.StringUtil;
import org.jsoup.nodes.Attribute;
import org.jsoup.nodes.Attributes;
import org.jsoup.select.NodeTraversor;
import org.jsoup.select.NodeVisitor;
import org.w3c.dom.Comment;
import org.w3c.dom.DOMImplementation;
import org.w3c.dom.Document;
import org.w3c.dom.DocumentType;
import org.w3c.dom.Element;
import org.w3c.dom.Text;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
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 java.io.StringWriter;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;
import java.util.Stack;

import static javax.xml.transform.OutputKeys.METHOD;


Helper class to transform a Document to a org.w3c.dom.Document, for integration with toolsets that use the W3C DOM. 
/**
 * Helper class to transform a {@link org.jsoup.nodes.Document} to a {@link org.w3c.dom.Document org.w3c.dom.Document},
 * for integration with toolsets that use the W3C DOM.
 */
public class W3CDom {
    protected DocumentBuilderFactory factory;

    public W3CDom() {
        factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);
    }

    
Converts a jsoup DOM to a W3C DOM

Params:
  • in – jsoup Document
Returns:W3C Document
/**
     * Converts a jsoup DOM to a W3C DOM
     *
     * @param in jsoup Document
     * @return W3C Document
     */
    public static Document convert(org.jsoup.nodes.Document in) {
        return (new W3CDom().fromJsoup(in));
    }

    
Serialize a W3C document to a String. Provide Properties to define output settings including if HTML or XML. If you don't provide the properties (null), the output will be auto-detected based on the content of the document. 
Params:
See Also:
Returns:Document as string
/**
     * Serialize a W3C document to a String. Provide Properties to define output settings including if HTML or XML. If
     * you don't provide the properties ({@code null}), the output will be auto-detected based on the content of the
     * document.
     *
     * @param doc Document
     * @param properties (optional/nullable) the output properties to use. See {@link
     *     Transformer#setOutputProperties(Properties)} and {@link OutputKeys}
     * @return Document as string
     * @see #OutputHtml
     * @see #OutputXml
     * @see OutputKeys#ENCODING
     * @see OutputKeys#OMIT_XML_DECLARATION
     * @see OutputKeys#STANDALONE
     * @see OutputKeys#STANDALONE
     * @see OutputKeys#DOCTYPE_PUBLIC
     * @see OutputKeys#DOCTYPE_PUBLIC
     * @see OutputKeys#CDATA_SECTION_ELEMENTS
     * @see OutputKeys#INDENT
     * @see OutputKeys#MEDIA_TYPE
     */
    public static String asString(Document doc, Map<String, String> properties) {
        try {
            DOMSource domSource = new DOMSource(doc);
            StringWriter writer = new StringWriter();
            StreamResult result = new StreamResult(writer);
            TransformerFactory tf = TransformerFactory.newInstance();
            Transformer transformer = tf.newTransformer();
            if (properties != null)
                transformer.setOutputProperties(propertiesFromMap(properties));

            if (doc.getDoctype() != null) {
                DocumentType doctype = doc.getDoctype();
                if (!StringUtil.isBlank(doctype.getPublicId()))
                    transformer.setOutputProperty(OutputKeys.DOCTYPE_PUBLIC, doctype.getPublicId());
                if (!StringUtil.isBlank(doctype.getSystemId()))
                    transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, doctype.getSystemId());
                    // handle <!doctype html> for legacy dom. TODO: nicer if <!doctype html>
                else if (doctype.getName().equalsIgnoreCase("html")
                    && StringUtil.isBlank(doctype.getPublicId())
                    && StringUtil.isBlank(doctype.getSystemId()))
                    transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, "about:legacy-compat");
            }

            transformer.transform(domSource, result);
            return writer.toString();

        } catch (TransformerException e) {
            throw new IllegalStateException(e);
        }
    }

    static Properties propertiesFromMap(Map<String, String> map) {
        Properties props = new Properties();
        props.putAll(map);
        return props;
    }

    
Canned default for HTML output. 
/** Canned default for HTML output. */
    public static HashMap<String, String> OutputHtml() {
        return methodMap("html");
    }

    
Canned default for XML output. 
/** Canned default for XML output. */
    public static HashMap<String, String> OutputXml() {
        return methodMap("xml");
    }

    private static HashMap<String, String> methodMap(String method) {
        HashMap<String, String> map = new HashMap<>();
        map.put(METHOD, method);
        return map;
    }

    
Convert a jsoup Document to a W3C Document.

Params:
  • in – jsoup doc
Returns:w3c doc
/**
     * Convert a jsoup Document to a W3C Document.
     *
     * @param in jsoup doc
     * @return w3c doc
     */
    public Document fromJsoup(org.jsoup.nodes.Document in) {
        Validate.notNull(in);
        DocumentBuilder builder;
        try {
            builder = factory.newDocumentBuilder();
            DOMImplementation impl = builder.getDOMImplementation();
            Document out;

            out = builder.newDocument();
            org.jsoup.nodes.DocumentType doctype = in.documentType();
            if (doctype != null) {
                org.w3c.dom.DocumentType documentType = impl.createDocumentType(doctype.name(), doctype.publicId(), doctype.systemId());
                out.appendChild(documentType);
            }
            out.setXmlStandalone(true);

            convert(in, out);
            return out;
        } catch (ParserConfigurationException e) {
            throw new IllegalStateException(e);
        }
    }

    
Converts a jsoup document into the provided W3C Document. If required, you can set options on the output document
before converting.

Params:
  • in – jsoup doc
  • out – w3c doc
See Also:
/**
     * Converts a jsoup document into the provided W3C Document. If required, you can set options on the output document
     * before converting.
     *
     * @param in jsoup doc
     * @param out w3c doc
     * @see org.jsoup.helper.W3CDom#fromJsoup(org.jsoup.nodes.Document)
     */
    public void convert(org.jsoup.nodes.Document in, Document out) {
        if (!StringUtil.isBlank(in.location()))
            out.setDocumentURI(in.location());

        org.jsoup.nodes.Element rootEl = in.child(0); // skip the #root node
        NodeTraversor.traverse(new W3CBuilder(out), rootEl);
    }

    
Serialize a W3C document to a String. The output format will be XML or HTML depending on the content of the doc.

Params:
  • doc – Document
See Also:
Returns:Document as string
/**
     * Serialize a W3C document to a String. The output format will be XML or HTML depending on the content of the doc.
     *
     * @param doc Document
     * @return Document as string
     * @see W3CDom#asString(Document, Map)
     */
    public String asString(Document doc) {
        return asString(doc, null);
    }

    
Implements the conversion by walking the input.

/**
     * Implements the conversion by walking the input.
     */
    protected static class W3CBuilder implements NodeVisitor {
        private static final String xmlnsKey = "xmlns";
        private static final String xmlnsPrefix = "xmlns:";

        private final Document doc;
        private final Stack<HashMap<String, String>> namespacesStack = new Stack<>(); // stack of namespaces, prefix => urn
        private Element dest;

        public W3CBuilder(Document doc) {
            this.doc = doc;
            this.namespacesStack.push(new HashMap<String, String>());
        }

        public void head(org.jsoup.nodes.Node source, int depth) {
            namespacesStack.push(new HashMap<>(namespacesStack.peek())); // inherit from above on the stack
            if (source instanceof org.jsoup.nodes.Element) {
                org.jsoup.nodes.Element sourceEl = (org.jsoup.nodes.Element) source;

                String prefix = updateNamespaces(sourceEl);
                String namespace = namespacesStack.peek().get(prefix);
                String tagName = sourceEl.tagName();

                Element el = namespace == null && tagName.contains(":") ?
                    doc.createElementNS("", tagName) : // doesn't have a real namespace defined
                    doc.createElementNS(namespace, tagName);
                copyAttributes(sourceEl, el);
                if (dest == null) { // sets up the root
                    doc.appendChild(el);
                } else {
                    dest.appendChild(el);
                }
                dest = el; // descend
            } else if (source instanceof org.jsoup.nodes.TextNode) {
                org.jsoup.nodes.TextNode sourceText = (org.jsoup.nodes.TextNode) source;
                Text text = doc.createTextNode(sourceText.getWholeText());
                dest.appendChild(text);
            } else if (source instanceof org.jsoup.nodes.Comment) {
                org.jsoup.nodes.Comment sourceComment = (org.jsoup.nodes.Comment) source;
                Comment comment = doc.createComment(sourceComment.getData());
                dest.appendChild(comment);
            } else if (source instanceof org.jsoup.nodes.DataNode) {
                org.jsoup.nodes.DataNode sourceData = (org.jsoup.nodes.DataNode) source;
                Text node = doc.createTextNode(sourceData.getWholeData());
                dest.appendChild(node);
            } else {
                // unhandled
                // not that doctype is not handled here - rather it is used in the initial doc creation
            }
        }

        public void tail(org.jsoup.nodes.Node source, int depth) {
            if (source instanceof org.jsoup.nodes.Element && dest.getParentNode() instanceof Element) {
                dest = (Element) dest.getParentNode(); // undescend. cromulent.
            }
            namespacesStack.pop();
        }

        private void copyAttributes(org.jsoup.nodes.Node source, Element el) {
            for (Attribute attribute : source.attributes()) {
                // valid xml attribute names are: ^[a-zA-Z_:][-a-zA-Z0-9_:.]
                String key = attribute.getKey().replaceAll("[^-a-zA-Z0-9_:.]", "");
                if (key.matches("[a-zA-Z_:][-a-zA-Z0-9_:.]*"))
                    el.setAttribute(key, attribute.getValue());
            }
        }

        
Finds any namespaces defined in this element. Returns any tag prefix.

/**
         * Finds any namespaces defined in this element. Returns any tag prefix.
         */
        private String updateNamespaces(org.jsoup.nodes.Element el) {
            // scan the element for namespace declarations
            // like: xmlns="blah" or xmlns:prefix="blah"
            Attributes attributes = el.attributes();
            for (Attribute attr : attributes) {
                String key = attr.getKey();
                String prefix;
                if (key.equals(xmlnsKey)) {
                    prefix = "";
                } else if (key.startsWith(xmlnsPrefix)) {
                    prefix = key.substring(xmlnsPrefix.length());
                } else {
                    continue;
                }
                namespacesStack.peek().put(prefix, attr.getValue());
            }

            // get the element prefix if any
            int pos = el.tagName().indexOf(":");
            return pos > 0 ? el.tagName().substring(0, pos) : "";
        }

    }
}