Java XPath Compile 无法查询具有唯一命名空间的标签

Question

我有一个标签，里面有一个唯一的命名空间，只有那个标签。我引入了 XML 命名空间上下文，但我的程序仍然返回 0 个节点。

// Create DocumentBuilderFactory for reading xml file
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        DocumentBuilder builder = factory.newDocumentBuilder();

        factory.setNamespaceAware(true);

        Document doc = builder.parse(new InputSource(new StringReader(text)));

        // Create XPathFactory for creating XPath Object
        XPathFactory xPathFactory = XPathFactory.newInstance();

        // Create XPath object from XPathFactory
        XPath xpath = xPathFactory.newXPath();

        xpath.setNamespaceContext(new NamespaceContext() {
            public String getNamespaceURI(String prefix) {
                if ("cam".equals(prefix))
                    return "urn:xxx:1.0:logging";
                else if ("soapenv".equals(prefix))
                    return "http://schemas.xmlsoap.org/soap/envelope/";
                else if ("xml".equals(prefix))
                    return XMLConstants.XML_NS_URI;
                return XMLConstants.NULL_NS_URI;
            }

            // This method isn't necessary for XPath processing.
            public String getPrefix(String uri) {
                throw new UnsupportedOperationException();
            }

            // This method isn't necessary for XPath processing either.
            public Iterator getPrefixes(String uri) {
                throw new UnsupportedOperationException();
            }
        });

        // Compile the XPath expression for getting the response
         XPathExpression xPathExpr =
         xpath.compile("/cam:message/cam:response/soapenv:Envelope/soapenv:Header/Info[1]/property[@name='response']/text()");
        

        // XPath text example : executing xpath expression in java
        // Object result = xPathExpr.evaluate(doc, XPathConstants.NODESET);
        // NodeList nodes = (NodeList) result;
        // int length = nodes.getLength();

        String result1 = (String) xPathExpr.evaluate(doc, XPathConstants.STRING);

XML 看起来像

 <cam:message xmlns="urn:xxx:1.0:logging">
         <cam:response>
           <soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:soapenc="http://schemas.xmlsoap.org/soap/encoding/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
               <soapenv:Header xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/">
                   <Info xmlns="urn:xxx:1.0:xxx.core.xxx.Service1">
                      <property name="response">some value</property>
                 </Info>
                 <Info xmlns="urn:xxx:1.0:xxx.core.xxx.Service2">
                      <property name="response">i am interested in this value</property>
                 </Info>
               </soapenv:Header>
           </soapenv:Envelope>
     </cam:response>
</cam:message>

所以标签<Info xmlns="urn:xxx:1.0:xxx.core.xxx.Service2">拥有自己的命名空间。我的程序没有为此返回值。同样有很多 Info 标签。我对命名空间以 Service2 结尾的第二个 Info 标记感兴趣。

Answer 1

您当前的 XPath 表达式仅匹配具有 no 命名空间 uri 的 Info 和 property 元素。

您必须将urn:...Service2-namespace 添加到您的NamespaceContext 内部类：

public String getNamespaceURI(String prefix) {
    if ("cam".equals(prefix))
       // like abvce
    else if ("s2".equals(prefix))
       return "urn:xxx:1.0:xxx.core.xxx.Service2";
    else
       return XMLConstants.NULL_NS_URI;
}

并相应地限定 XPath 中的 Info 和 property 步骤，使用前缀 s2：

xpath.compile("/cam:message/cam:response/soapenv:Envelope/soapenv:Header/s2:Info/s2:property[@name='response']/text()");

除此之外，您的代码和 XML 文件中存在错误：

a) 在创建 DocumentBuilder之后让 DocumentBuilderFactory 感知命名空间。改为写：

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder builder = factory.newDocumentBuilder();

b) 您的 XML 使用前缀 cam，该前缀未在根元素中正确声明。改为写：

<cam:message xmlns:cam="urn:xxx:1.0:logging">
    ....