XPath哪里出错了?

I am trying to manipulate xsd schema as an xml document that should not be a problem, I believe. But facing troubles with XPath. Whatever XPath I try, it returns nothing. Tried it with or without namespaces but no success. Please help me understand what am I doing wrong?

我正在尝试将xsd模式作为一个xml文档进行操作，我认为这应该不是一个问题。但是要面对XPath的问题。无论我尝试什么XPath，它都不会返回任何内容。尝试使用或没有名称空间，但没有成功。请帮助我理解我做错了什么?

My xml is:

我的xml是:

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" targetNamespace="http://www.mydomain.com" xmlns="http://www.mydomain.com" elementFormDefault="qualified">

  <xs:complexType name="Label">
    <xs:choice maxOccurs="unbounded" minOccurs="0">
      <xs:element name="Listener"/>
    </xs:choice>
  </xs:complexType>

</xs:schema>

and application code is:

和应用程序代码是:

DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
domFactory.setValidating(false);
domFactory.setNamespaceAware(true);
domFactory.setIgnoringComments(true);
domFactory.setIgnoringElementContentWhitespace(true);

try {
    DocumentBuilder builder = domFactory.newDocumentBuilder();
    Document dDoc = builder.parse("C:/Temp/test.xsd");

    // This part works
    Node rootNode = dDoc.getElementsByTagName("xs:schema").item(0);
    System.out.println(rootNode.getNodeName());

    // This part doesn't work
    XPath xPath1 = XPathFactory.newInstance().newXPath();
    NodeList nList1 = (NodeList) xPath1.evaluate("//xs:schema", dDoc, XPathConstants.NODESET);  
    System.out.println(nList1.item(0).getNodeName());

    // This part doesn't work
    XPath xPath2 = XPathFactory.newInstance().newXPath();
    NodeList nList2 = (NodeList) xPath2.evaluate("//xs:element", rootNode, XPathConstants.NODESET); 
    System.out.println(nList2.item(0).getNodeName());

}catch (Exception e){
    e.printStackTrace();
}

3 个解决方案

#1

Set a namespace context using XPath.setNamespaceContext(). This binds the xs prefix to the http://www.w3.org/2001/XMLSchema namespace.

使用XPath.setNamespaceContext()设置名称空间上下文。这将xs前缀绑定到http://www.w3.org/2001/XMLSchema名称空间。

#2

Made changes to your code. It works:

对代码做了修改。工作原理:

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;

import javax.xml.namespace.NamespaceContext;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

public class XPathtest {
    public static void main(String[] args) {
        DocumentBuilderFactory domFactory = DocumentBuilderFactory
                .newInstance();
        domFactory.setValidating(false);
        domFactory.setNamespaceAware(true);
        domFactory.setIgnoringComments(true);
        domFactory.setIgnoringElementContentWhitespace(true);

        try {
            DocumentBuilder builder = domFactory.newDocumentBuilder();
            Document dDoc = builder.parse("C:/Temp/test.xsd");

            // This part works
            Node rootNode = dDoc.getElementsByTagName("xs:schema").item(0);
            System.out.println(rootNode.getNodeName());

            // This part doesn't work
            XPath xPath1 = XPathFactory.newInstance().newXPath();

            NamespaceContext nsContext = new NamespaceContext() {

                @Override
                public String getNamespaceURI(String prefix) {
                    return "http://www.w3.org/2001/XMLSchema";
                }

                @Override
                public String getPrefix(String namespaceURI) {
                    return "xs";
                }

                @Override
                public Iterator getPrefixes(String namespaceURI) {
                    Set s = new HashSet();
                    s.add("xs");
                    return s.iterator();
                }

            };

            xPath1.setNamespaceContext((NamespaceContext) nsContext);

            NodeList nList1 = (NodeList) xPath1.evaluate("//xs:schema", dDoc,
                    XPathConstants.NODESET);
            System.out.println(nList1.item(0).getNodeName());

            // This part doesn't work
            // XPath xPath2 = XPathFactory.newInstance().newXPath();
            NodeList nList2 = (NodeList) xPath1.evaluate("//xs:element",
                    rootNode, XPathConstants.NODESET);
            System.out.println(nList2.item(0).getNodeName());

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

#3

The reason is that you haven't specified what xs means. An xml parser must know the namespace url, xs is just an identifier.

原因是您没有指定xs的含义。xml解析器必须知道名称空间url, xs只是一个标识符。

You can demonstrate this yourself by using the following code:

您可以使用以下代码自己演示:

XPath xPath = XPathFactory.newInstance().newXPath();

SimpleNamespaceContext nsContext = new SimpleNamespaceContext();
nsContext.addNamespace("t", "http://www.w3.org/2001/XMLSchema");
xPath.setNamespaceContext(nsContext);

xPath.evaluate("//t:schema", dDoc, XPathConstants.NODESET);

You can see that I now use the identifier t instead of xs but that doesn't matter as long as you use the same namespace url.

您可以看到，我现在使用标识符t而不是xs，但是只要使用相同的名称空间url，这就不重要了。

#1