在Java中提取嵌套的html标签？

Question

I have the following HTML fragment:

String source = "<p>dsdds</p>"
                + "<ul class=\"some-class-name\">"
                + "<li>data</li>"
                + "<li><div><ul><li>data</li></ul></div></li>"
                + "</ul>"
                + "<p>data</p>"
                + "<ul>data</ul><div>data</div>";

What I want to achieve is to get the result as:

<ul class="some-class-name">
    <li>data</li>
    <li><div><ul><li>data</li></ul></div></li>
</ul>

What I have tried so far:

        String endTag = "</ul>";
        int origin = source.indexOf("<ul class=\"some-class-name\">");
        int currentFrom = origin;
        int to = source.indexOf(endTag, currentFrom);
        while (true) {
            int curIndex = source.indexOf("<ul", currentFrom + 1);
            if (curIndex > -1) {
                currentFrom = curIndex;
                to = source.indexOf(endTag, currentFrom);
            } else {
                to = source.indexOf(endTag, to);
                break;
            }
        }
        System.out.println(source.substring(origin, to + endTag.length()));

But I always get:

<ul class="some-class-name">
    <li>data</li>
    <li><div><ul><li>data</li></ul></div></li>
</ul>
<p>data</p>
<ul>data</ul>

Can anyone help me fix my code? Or suggest another approach.

Edit: Please do not suggest built in libraries such as Jsoup.

Answer 1

Luckily, your fragment is valid XHTML, which means it is valid XML.

XPath is specifically designed to extract nodes from XML:

// Must have a single root in order to parse.
String input = "<div>" + source + "</div>";

XPath xpath = XPathFactory.newInstance().newXPath();
Node node = (Node)
    xpath.evaluate("//ul[@class='some-class-name']",
        new InputSource(new StringReader(input)),
        XPathConstants.NODE);

StringWriter result = new StringWriter();
Transformer transformer =
    TransformerFactory.newInstance().newTransformer();
transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
transformer.transform(new DOMSource(node), new StreamResult(result));

String fragment = result.toString();

Answer 2

You should use jsoup: Java HTML Parser like this.

Document doc = Jsoup.parse(source);
Element e = doc.select("ul.some-class-name").first();
System.out.println(e);

result:

<ul class="some-class-name">
 <li>data</li>
 <li>
  <div>
   <ul>
    <li>data</li>
   </ul>
  </div></li>
</ul>