Java XPath评估始终为null

Question

我现在正在研究这几天，我不知道为什么我无法让它发挥作用。我创建了一些java代码：

DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setNamespaceAware(true);
DocumentBuilder builder;
Document doc = null;
try {
    builder = factory.newDocumentBuilder();
    doc = builder.parse(xsl);

    XPathFactory xpathFactory = XPathFactory.newInstance();
    XPath xpath = xpathFactory.newXPath();

    try {
        XPathExpression expr = xpath.compile("//xs:attribute-set[@name = \"tableImportantLine\"]/xs:attribute/text()");
        NodeList nl = (NodeList) expr.evaluate(doc, XPathConstants.NODESET);
    } catch (XPathExpressionException e) {
        e.printStackTrace();
    }

} catch (ParserConfigurationException | SAXException | IOException e) {
    e.printStackTrace();
}

应该读取这个xsl-fo文件：

<?xml version="1.0" encoding="utf-8"?>
<xs:stylesheet xmlns:xs="http://www.w3.org/1999/XSL/Transform" xmlns:fo="http://www.w3.org/1999/XSL/Format" version="1.0">
  <xs:attribute-set name="cell-style">
    <xs:attribute name="border-width">0.5pt</xs:attribute>
    <xs:attribute name="border-style">solid</xs:attribute>
    <xs:attribute name="border-color">black</xs:attribute>
  </xs:attribute-set>
  <xs:attribute-set name="block-style">
    <xs:attribute name="font-size">  10pt</xs:attribute>
    <xs:attribute name="line-height">15pt</xs:attribute>
    <xs:attribute name="start-indent">1mm</xs:attribute>
    <xs:attribute name="end-indent">  1mm</xs:attribute>
  </xs:attribute-set>

  <xs:attribute-set name="thickText">
    <xs:attribute name="font-weight">bold</xs:attribute>
  </xs:attribute-set>

  <xs:attribute-set name="tableImportantLine">
    <xs:attribute name="background-color">#86f442</xs:attribute>
  </xs:attribute-set>


  <xs:attribute-set name="tableOutlineStyle">
    <xs:attribute name="border">solid 0.5mm black</xs:attribute>
  </xs:attribute-set>

  <xs:attribute-set name="tableStyle">
    <xs:attribute name="border">solid 0.1mm black</xs:attribute>
    <xs:attribute name="text-align">center</xs:attribute>
  </xs:attribute-set>

  <xs:attribute-set name="tableHeaderStyle">
    <xs:attribute name="border">solid 0.1mm black</xs:attribute>
    <xs:attribute name="text-align">center</xs:attribute>
    <xs:attribute name="font-weight">bold</xs:attribute>
  </xs:attribute-set>

  <xs:attribute-set name="stripedDesign">
    <xs:attribute name="background-color">#123FC2</xs:attribute>
  </xs:attribute-set>

</xs:stylesheet>

我删除了fo-templates，因为它们非常大并且编译没有问题（apache-fop）。 我已经检查了我的XPath，它应该可以完美地运行到＃86f442＆＃39;。尽管如此，XPath选择器始终返回0个节点并且为空... 该文档包含xml。 感谢任何帮助过的人。

//编辑： 我还尝试直接选择＆＃39; // xs：attribute-set＆＃39;而不是更具体的xpath选择器。仍然只返回一个空节点列表。 使用

时也是如此

  

String node = expr.evaluate（doc）;

带

  

// xs：attribute-set [@name =   \＆＃34; tableImportantLine \＆＃34;] / XS：属性/文本（）

返回null ..