In Java, How Do I Parse Xml as a String Instead of a File?

One way is to use the version of parse that takes an InputSource rather than a file

A SAX InputSource can be constructed from a Reader object. One Reader object is the StringReader

So something like

parse(new InputSource(new StringReader(myString))) may work. 

Convert the string to an InputStream and pass it to DocumentBuilder

final InputStream stream = new ByteArrayInputStream(string.getBytes(StandardCharsets.UTF_8));
DocumentBuilder builder = DocumentBuilderFactory.newInstance().newDocumentBuilder();
builder.parse(stream);

EDIT
In response to bendin's comment regarding encoding, see shsteimer's answer to this question.

I'm using this method

public Document parseXmlFromString(String xmlString){
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    DocumentBuilder builder = factory.newDocumentBuilder();
    InputStream inputStream = new    ByteArrayInputStream(xmlString.getBytes());
    org.w3c.dom.Document document = builder.parse(inputStream);
    return document;
}

javadocs show that the parse method is overloaded.

Create a StringStream or InputSource using your string XML and you should be set.

You can use the Scilca XML Progession package available at GitHub.

XMLIterator xi = new VirtualXML.XMLIterator("<xml />");
XMLReader xr = new XMLReader(xi);
Document d = xr.parseDocument();