The upload-charset-finder-class Element
It specifies the finder that determines charset (aka.., encoding) for the uploaded text files if no charset is specified with the content type.
If the uploaded file is binary, there is no encoding issue at all.
The finder must implement the CharsetFinder interface. Then, when a text file is uploaded, the getCharset method is called and it can determines the encoding based on the content type and/or the content of the uploaded file.
Notice that it has the higher priority than the upload-charset element, see above.