Java, XPath - how to get the entire node base on specific element

Question

I have the following XML structure

<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>

How can I construct the query to get the first name of students who have the first mark over 50? I'm doing this and I can see there is one result which what I expect but it doesn't print out anything.

    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());
    }

Thanks.

R.yan · Accepted Answer · 2018-04-12 07:54:03Z

2

you just need to simply change your Xpath expression to follow: String expression = "/students/student[marks/first > 50]/firstname/text()"

And your for-loop to:

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

Output:

1
Emily

answered Apr 12, 2018 at 7:54

R.yan

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Comments

Fabian · Accepted Answer · 2018-04-12 08:00:14Z

GetFirstChild() and getChildNodes() yield not only child element nodes but also text nodes. The first node you get will be a text node (just whitespace characters and a line break).

Example:

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());
            }
        }
    }

Output:

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: '
'

EDIT: Changed example to output student names, not student marks

This is for clarification. If you just need to output the student names and nothing else, you can of course simple change the xpath query, as R.yan suggested.

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