NamespaceContext 以及通过 XPath 使用命名空间

使用XPath进行命名空间的处理是在XML文档中定位节点的一种方法。在XML中，命名空间用于避免元素和属性名称的冲突，并将它们分组到不同的命名空间中。在Java中，可以通过使用NamespaceContext接口来处理命名空间，并在XPath表达式中使用这些命名空间。

java
import javax.xml.namespace.NamespaceContext;
import java.util.Iterator;
public class MyNamespaceContext implements NamespaceContext {
    @Override
    public String getNamespaceURI(String prefix) {
        if ("ns".equals(prefix)) {
            return "http://www.example.com/namespace";
        }
        return null;
    }
    @Override
    public String getPrefix(String namespaceURI) {
        if ("http://www.example.com/namespace".equals(namespaceURI)) {
            return "ns";
        }
        return null;
    }
    @Override
    public Iterator getPrefixes(String namespaceURI) {
        return null;
    }
}

java
import org.w3c.dom.Document;
import org.w3c.dom.NodeList;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpression;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;
public class XPathNamespaceExample {
    public static void main(String[] args) {
        try {
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
            DocumentBuilder builder = factory.newDocumentBuilder();
            Document doc = builder.parse("example.xml");
            XPathFactory xpathFactory = XPathFactory.newInstance();
            XPath xpath = xpathFactory.newXPath();
            xpath.setNamespaceContext(new MyNamespaceContext());
            XPathExpression expr = xpath.compile("/ns:root/ns:element");
            NodeList nodeList = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
            for (int i = 0; i < nodeList.getLength(); i++) {
                System.out.println(nodeList.item(i).getTextContent());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}