Getting error in parsing an XML file using JDOM

I have this XML document:

<?xml vers开发者_运维技巧ion="1.0" encoding="utf-8"?>
<RootElement>
   <Achild>
      .....
   </Achild>
</RootElement>

How can I check if the document contains Achild element or not? I tried

final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
// Use the factory to create a builder
try {
    final DocumentBuilder builder = factory.newDocumentBuilder();
    final Document doc = builder.parse(configFile);
    final Node parentNode = doc.getDocumentElement();
    final Element childElement = (Element) parentNode.getFirstChild();
    if(childElement.getNodeName().equalsIgnoreCase(...

but it gives me an error (childElement is null).

I think that you're getting #text node (that between <RootElement> and <Achild>) as first child (that's pretty common mistake), for example:

final Node parentNode = doc.getDocumentElement();
Node childElement = parentNode.getFirstChild();
System.out.println(childElement.getNodeName());

Returns:

#text

Use instead:

final Node parentNode = doc.getDocumentElement();
NodeList childElements = parentNode.getChildNodes();
for (int i = 0; i < childElements.getLength(); ++i)
{
    Node childElement = childElements.item(i);
    if (childElement instanceof Element)
        System.out.println(childElement.getNodeName());
}

Wanted result:

Achild

EDIT:

There is second way using DocumentBuilderFactory.setIgnoringElementContentWhitespace method:

factory.setIgnoringElementContentWhitespace(true);

However this works only in validating mode, so you need to provide DTD in your XML document:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE RootElement [
    <!ELEMENT RootElement (Achild)+>
    <!ELEMENT Achild (#PCDATA)>
]>
<RootElement>
   <Achild>some text</Achild>
</RootElement>

and set factory.setValidating(true). Full example:

final DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setValidating(true);
factory.setIgnoringElementContentWhitespace(true);
final DocumentBuilder builder = factory.newDocumentBuilder();
final Document doc = builder.parse("input.xml");

final Node rootNode = doc.getDocumentElement();
final Element childElement = (Element) rootNode.getFirstChild();

System.out.println(childElement.getNodeName());

Wanted result with original code:

Achild

It sounds like .getFirstChild() is returning you a text node containing the white space between "" and "", in which case you would need to advance to the next sibling node to get to where you expect.