XMLParsing, Dynamic Structure, Content

The right tool for this job is xpath It allows you to collect all or some elements and attributes based on various criteria. It is the closest you will get to a "universal" xml parser.

Here is the solution that I came up with. The solution first finds all element names in the given xml doc, then for each element, it counts the element's occurrences, then collect it all to a map. same for attributes.
I added inline comments and method/variable names should be self explanatory.

import java.io.*;
import java.nio.file.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

import org.w3c.dom.*;

import javax.xml.parsers.*;
import javax.xml.xpath.*;

public class TestXpath
{

    public static void main(String[] args) {

        XPath xPath = XPathFactory.newInstance().newXPath();

        try (InputStream is = Files.newInputStream(Paths.get("C://temp/test.xml"))) {
            // parse file into xml doc
            DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
            Document xmlDocument = builder.parse(is);

            // find all element names in xml doc
            Set<String> allElementNames = findNames(xmlDocument, xPath.compile("//*[name()]"));
            // for each name, count occurrences, and collect to map
            Map<String, Integer> elementsAndOccurrences = allElementNames.stream()
                .collect(Collectors.toMap(Function.identity(), name -> countElementOccurrences(xmlDocument, name)));
            System.out.println(elementsAndOccurrences);

            // find all attribute names in xml doc
            Set<String> allAttributeNames = findNames(xmlDocument, xPath.compile("//@*"));
            // for each name, count occurrences, and collect to map
            Map<String, Integer> attributesAndOccurrences = allAttributeNames.stream()
                .collect(Collectors.toMap(Function.identity(), name -> countAttributeOccurrences(xmlDocument, name)));
            System.out.println(attributesAndOccurrences);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static Set<String> findNames(Document xmlDoc, XPathExpression xpathExpr) {
        try {
            NodeList nodeList = (NodeList)xpathExpr.evaluate(xmlDoc, XPathConstants.NODESET);
            // convert nodeList to set of node names
            return IntStream.range(0, nodeList.getLength())
                .mapToObj(i -> nodeList.item(i).getNodeName())
                .collect(Collectors.toSet());
        } catch (XPathExpressionException e) {
            e.printStackTrace();
        }
        return new HashSet<>();
    }

    public static int countElementOccurrences(Document xmlDoc, String elementName) {
        return countOccurrences(xmlDoc, elementName, "count(//*[name()='" + elementName + "'])");
    }

    public static int countAttributeOccurrences(Document xmlDoc, String attributeName) {
        return countOccurrences(xmlDoc, attributeName, "count(//@*[name()='" + attributeName + "'])");
    }

    public static int countOccurrences(Document xmlDoc, String name, String xpathExpr) {
        XPath xPath = XPathFactory.newInstance().newXPath();
        try {
            Number count = (Number)xPath.compile(xpathExpr).evaluate(xmlDoc, XPathConstants.NUMBER);
            return count.intValue();
        } catch (XPathExpressionException e) {
            e.printStackTrace();
        }
        return 0;
    }
}