Java CSV to XML converter
Line by line analysis
public class Util {

Util is not a good class name. It does not describe what the responsibility or function of the class is. If it did, it would describe the top desktop drawer of code, where all random code snippets are dumped because the authors could not be bothered to think of a proper place. Suffice to say, those kinds of classes don't exist in well maintained code bases. Use something like TabularToXmlConverter instead.
/*/
DOC Generation -&gt; XML with ArrayList String elements
 */

You should have an extremely good reason for creating your own specialized format for documenting your classes and methods. Java platform comes with JavaDoc which is a standardized way of formatting documentation. Programmers know how to read it and expect to see it. When encountered with your style they literally get angry because they have to learn a new (and most likely inferior) format.
DocumentBuilderFactory xmlFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder xmlBuilder = xmlFactory.newDocumentBuilder();

Because your method created the DocumentBuilderFactory, it became responsible for managing it's own dependencies. If you wanted to use the converter to create a bit different kind of XML document, you couldn't do it without changing the class and breaking all code that already uses it. You might want to pass a DocumentBuilder reference to the class and thus employ dependency injection.
Document xmlDoc = xmlBuilder.newDocument();

What is the reason why you build the document in memory? Most often when I have worked with XML, the biggest problem has been memory consumption caused by handling large XML documents that have been loaded into memory. Since you also provided a transformDocToFile it might make more sense to just write the document directly to an OutputStream using the Streaming API for XML (StAX).
boolean headerDefined = false; //First while will be to define header

Do not use end-of-line comments. They are difficult to read, hard to maintain and force you to compress your thoughts into fewer words that make sense. I, for example, have no idea what this comment means. And you should strive to use variable names that describe the purpose of the variable. From the variable name alone I already guessed it's a flag that tells if the header row has been generated. So there isn't any need for a comment here at all. The other end-of-line comments also just tell what the preceding code does adding no additional value. Comments should desribe why something is being done, not repeat what the code already tells. If the code isn't clear, first priority should be making it clearer instead of duplicating it in free verse.
public static void transformDocToFile(Document xmlDoc, String xmlFile) throws TransformerException {

One of your methods is static and the other is not, requiring the caller to create an unnecessary instance of the Util-class.
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    }

You catch one of the possible exceptions and continue happily even though in this particular case you cannot even write to the file.