How can I parse an XML from String?

I've used following code to parse XML file.
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DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
factory.setIgnoringElementContentWhitespace(true);
factory.setIgnoringComments(true);
DocumentBuilder builder = factory.newDocumentBuilder();
Document XMLDoc = builder.parse(fileName);
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builder.parse(...) does not take String input... please help.