java - 如何使用 jdom 检查文件中是否存在元素

Question

我有一个这样的 XML 文件:

<?xml version="1.0" encoding="utf-8"?>
<RootElement>
 <Achild>
  .....
 </Achild>
 </RootElement>

我如何检查文件是否包含 Achild 元素......？

            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(....

但是它给我的错误是 childElement is null....

Answer 1

SAXBuilder builder = new SAXBuilder();
Document document = builder.build(new File("foo.xml"));

XPath xPath = XPath.newInstance("/RootElement/Achild");

/*If you want to find all the "Achild" elements 
and do not know what the document structure is, 
use the following XPath instead(less efficient):
XPath xPath = XPath.newInstance("//Achild");
*/

Element aChild = (Element) xPath.selectSingleNode(document);

if(aChild == null){
  //There is at least one "Achild" element in the document
} else{
  //No "Achild" elements found
}