MultiPartParserDefinition:192

• MultiPartUploadHandler doesn't use defaultEncoding and instead gets encoding from the HTTP request.

The issue:

• When you send data via JavaScript using XMLHttpRequest and FormData the request is encoded as UTF-8 (this cannot be changed and the charset isn't specified since that is the default) as a result the MultipartParser will use the HTTP default which is ISO-8859-1
• The server default can be changed by adding e.g. <default-encoding>UTF-8</default-encoding> to jboss-web.xml, this changes the defaultEncoding of the parser
• Since the MultiPartUploadHandler ignores this setting the request is still parsed by iso-8859-1 however request.getCharacterEncoding() will return "UTF-8"

fd = new FormData();
fd.append("ěščř","");
xhr = new XMLHttpRequest();
xhr.open('POST', "");
xhr.send(fd);