JAVA: Read xml with iterated child node names

Question

To migrate from an old XML-based application to a database application I need to implement a converter that reads XML files and creates a file with insert queries

I've taken a look at common tutorials for java XML reading, but my issue is, that I do not have Nodes with the same name, but unique node names following a certain prefix.

Most Tutorial Examples follow a scheme like this:

<root>
 <class>
  <node></node>
  <node></node>
  <node></node>
 </class>
</root>

which allows the usage of doc.getElementsByTagName("theName"). But in my case, the tagname is a prefix followed by unique identifier, like <theNodeName_A1>. Here is a sample of my XML. each <theNodeName_XX> contains multiple children and children of children.

<root>
 <class>
  <theNodeName_A1>
  </theNodeName_A1>
  <theNodeName_B3>
  </theNodeName_B3>
 </class>
</root>

My goal is to provide a function that does something like "doc.getElementsbyTagName(contains("theNodeName")) which would allow to iterate through each node and process child (subnodes) of each node.

How can I achieve this?

Answer 1

getElementsByTagName is not going to work for this. I think the easiest approach is to use XPath:

XPath xpath = XPathFactory.newInstance().newXPath();
NodeList elements = (NodeList) xpath.evaluate(
    "//class/*[contains(local-name(), '_')]",
    doc, XPathConstants.NODESET);

int count = elements.getLength();
for (int i = 0; i < count; i++) {
    Element element = (Element) elements.item(i);
    String name = element.getTagName();
    int underscore = name.indexOf('_');
    String id = name.substring(underscore + 1);
    // ...
}

You could also iterate over the child elements one by one, but it’s more involved:

NodeList classElements = doc.getElementsByTagName("class");
int classCount = classElements.getLength();
for (int i = 0; i < classCount; i++) {
    Element classElement = (Element) classElements.item(i);

    NodeList children = classElement.getChildNodes();
    int childCount = children.getLength();
    for (int j = 0; j < childCount; j++) {
        Node child = children.item(j);

        // IMPORTANT:  Not all child nodes are Elements.
        // DO NOT SKIP THIS CHECK!
        if (child instanceof Element) {
            Element element = (Element) child;
            String name = element.getTagName();
            int underscore = name.indexOf('_');
            if (underscore > 0) {
                String id = name.substring(underscore + 1);
                // ...
            }
        }
    }
}