使用Java将XML文件解析为DOM时如何跳过某些元素

Question

I am attempting to parse some XML documents into DOM so that I can run XPath queries against it. My code is in Java and have been using the Xerces org.apache.xerces.parsers.DOMParser implementation.

I am only interested in certain portions of the XML, under element elementICareAbout and can ignore other elements.

<top>
   <elementICareAbout>...</elementICareAbout>
   <elementToIgnore>...</elementToIgnore>
</top>

The XML file size can be quite large, and I would not like to have to hold onto elements in memory which I would not need as part of the processing, where I would expect an XPath query to /top/elementICareAbout to return data, but /top/elementToIgnore would just return nothing (as I don't need it to).

Looking over the Xerces DOMParser or the JAXP APIs I don't see any kind of way to explicitly ignore certain elements so that they are not part of the DOM tree in memory after parsed?

Is there a good way to construct a partial DOM Document from an XML file tailored to the parts that I need?

Answer 1

You could write a SAX filter and insert it into the processing pipeline between the (SAX) parser and the document builder. Or with rather less coding you could write an XSLT 3.0 streaming transformation. Or you could write an XQuery to select the parts of the document you want, and run it using a query processor that supports document projection. It all depends how wedded you are to Java/DOM coding - my preference would be for higher-level languages than that.

Answer 2

You can also get the element by tagname. For example, if you have a xml files call Question.xml. Question.xml In the java file, you can do the following:

      DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
       DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
       InputSource is = new InputSource(new StringReader(responseString));
       Document doc = dBuilder.parse(is);

       doc.getDocumentElement().normalize();

       NodeList nList = doc.getElementsByTagName("Question");

       //get all lessons stored
       for (int temp = 0; temp < nList.getLength(); temp++) {

           Node nNode = nList.item(temp);

           if (nNode.getNodeType() == Node.ELEMENT_NODE) {

               Element eElement = (Element) nNode;

               //Looking through elements by tagname
               String q1 = eElement.getElementsByTagName("q1").item(0).getTextContent();