ServletFileUpload.isMultipartContent() is commented out. The comment says "This method cannot be enabled until the one in FileUploadBase is removed, since it is not possible to override a static method." That's wrong. It IS possible to override a static method, but it is NOT possible to override a
final method. The two FileUploadBase.isMultipartContent() methods are not only static, they are
final.
-> remove the final modifier from the FileUploadBase.isMultipartContent() methods, comment in ServletFileUpload.isMultipartContent() - voila.
P.S.: to be precise, you cannot 'override' a static method, but you can 'hide' it... See http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.4.8.2