Java – Handling Empty Tags in XML using Sax Parser, Java

javasaxsaxparserxml

I'm Using a Sax parser to handle a pre-written XML file….i have no way of changing the XML as it is held by another application but need to parse data from it. The XML file contains a Tag
< ERROR_TEXT/>
which is empty when no error is occurred.
as a result the parser takes the next character after the tag close which is "\n".
I have tried
result.replaceAll("\n", "");
and
result.replaceAll("\n", "");

how do I get SAX to recognize this is an empty tag and return the value as "" ?

Best Answer

You DO THAT. If you have xml and Java source blow.

<ERROR_TEXT>easy</ERROR_TEXT><ERROR_TEXT/>

Java code

private boolean isKeySet = false;
private String key = "";
@Override
public void characters(
    char[] ch,
    int start,
    int length
) throws SAXException
{
    if (!isKeySet) {
        return;
    }
    isKeySet = false;
    logger.debug("key : [" + key + "], value : [" + value + "]");
}
@Override
public void startElement(
    String uri,
    String localName,
    String qName,
    Attributes attrs
) throws SAXException
{
    key = qName;
    isKeySet = true;
}

@Override
public void endElement(
    String uri,
    String localName,
    String qName
) throws SAXException
{
    if (isKeySet) {
        isKeySet = false;
        logger.debug("key : [" + key + "](EMPTY!!!)");
    }
}

RESULT log:

key : [ERROR_TEXT], value : [easy]

key : [ERROR_TEXT](EMPTY!!!)

Call flow: startElement() -> characters() -> endElement() -> startElement() -> endElement() -> characters()

That's it! THE END

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You can use that style of comment across multiple lines (which exists also in HTML)

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Java – How to read XML using XPath in Java

You need something along the lines of this:

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(<uri_as_string>);
XPathFactory xPathfactory = XPathFactory.newInstance();
XPath xpath = xPathfactory.newXPath();
XPathExpression expr = xpath.compile(<xpath_expression>);

Then you call expr.evaluate() passing in the document defined in that code and the return type you are expecting, and cast the result to the object type of the result.

If you need help with a specific XPath expressions, you should probably ask it as separate questions (unless that was your question in the first place here - I understood your question to be how to use the API in Java).

Edit: (Response to comment): This XPath expression will get you the text of the first URL element under PowerBuilder:

/howto/topic[@name='PowerBuilder']/url/text()

This will get you the second:

/howto/topic[@name='PowerBuilder']/url[2]/text()

You get that with this code:

expr.evaluate(doc, XPathConstants.STRING);

If you don't know how many URLs are in a given node, then you should rather do something like this:

XPathExpression expr = xpath.compile("/howto/topic[@name='PowerBuilder']/url");
NodeList nl = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);

And then loop over the NodeList.

Best Answer

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