On September 28, 2009 the Apache POI project released version 3.5 which officially supports the OOXML formats introduced in Office 2007, like DOCX and XLSX.
This worked for me. Make sure you add the required jars (upgrade xmlbeans, etc.)
public String extractText(InputStream in) throws Exception {
XWPFDocument doc = new XWPFDocument(in);
XWPFWordExtractor ex = new XWPFWordExtractor(doc);
String text = ex.getText();
return text;
}