Java，XPath - 如何根据特定元素获取整个节点

Question

我有以下 XML 结构

<students>
<student studentnumber="1">
    <firstname>Charlie</firstname>
    <lastname>Davies</lastname>
    <marks>
        <first>12</first>
        <second>52</second>
        <third>98</third>
        <forth>32</forth>
    </marks>
</student>
<student studentnumber="2">
    <firstname>Emily</firstname>
    <lastname>Roberts</lastname>
    <marks>
        <first>55</first>
        <second>51</second>
        <third>57</third>
        <forth>84</forth>
    </marks>
</student>

如何构造查询以获取第一分超过 50 的学生的名字？我正在这样做，我可以看到有一个结果符合我的预期，但它没有打印出任何内容。

    String expression = "/students/student[marks/first > 50]";
    NodeList nodes = (NodeList) xPath.compile(expression).evaluate(xmlDocument, XPathConstants.NODESET);

    System.out.println(nodes.getLength());

    for (int i = 0; i < nodes.getLength(); ++i) {
        System.out.println(nodes.item(i).getFirstChild().getNodeValue());
    }

谢谢。

Answer 1

您只需要简单地更改您的 Xpath 表达式即可： String expression = "/students/student[marks/first > 50]/firstname/text()"

你的 for 循环：

for (int i = 0; i < nodes.getLength(); i++) {
    System.out.println(nodes.item(i).getNodeValue());
}

输出：

1
Emily

Answer 2

GetFirstChild() 和 getChildNodes() 不仅产生子元素节点，而且产生文本节点。您获得的第一个节点将是一个文本节点（只有空格字符和换行符）。

例子：

String expression = "/students/student[marks/first > 50]";
NodeList nodes = (NodeList) 
xPath.compile(expression).evaluate(xmlDocument, XPathConstants.NODESET);


 for (int i = 0; i < nodes.getLength(); ++i) {
        Node n = nodes.item(i);
        for (int j = 0; j < n.getChildNodes().getLength(); ++j) {
            Node n1 = n.getChildNodes().item(j);
            System.out.println("Level 1 node type: " + n1.getNodeType());
            System.out.println("Level 1 node value: " + n1.getNodeValue());
            for (int k = 0; k < n1.getChildNodes().getLength(); ++k) {
                Node n2 = n1.getChildNodes().item(k);
                System.out.println("  Level 2 node type: " + n2.getNodeType());
                System.out.println("  Level 2 Node value: " + n2.getNodeValue());
            }
        }
    }

输出：

1
Level 1 node type: 3
Level 1 node value: '
    '
Level 1 node type: 1
Level 1 node value: 'null'
  Level 2 node type: 3
  Level 2 Node value: 'Emily'
Level 1 node type: 3
Level 1 node value: '
    '
Level 1 node type: 1
Level 1 node value: 'null'
  Level 2 node type: 3
  Level 2 Node value: 'Roberts'
Level 1 node type: 3
Level 1 node value: '
    '
Level 1 node type: 1
Level 1 node value: 'null'
  Level 2 node type: 3
  Level 2 Node value: '
        '
  Level 2 node type: 1
  Level 2 Node value: 'null'
  Level 2 node type: 3
  Level 2 Node value: '
        '
  Level 2 node type: 1
  Level 2 Node value: 'null'
  Level 2 node type: 3
  Level 2 Node value: '
        '
  Level 2 node type: 1
  Level 2 Node value: 'null'
  Level 2 node type: 3
  Level 2 Node value: '
        '
  Level 2 node type: 1
  Level 2 Node value: 'null'
  Level 2 node type: 3
  Level 2 Node value: '
    '
Level 1 node type: 3
Level 1 node value: '
'

编辑：将示例更改为输出学生姓名，而不是学生分数