“Content is not allowed in prolog” when parsing perfectly valid XML on GAE

Question

I\'ve been beating my head against this absolutely infuriating bug for the last 48 hours, so I thought I\'d finally throw in the towel and try asking here before I throw my

Answer 1

In my xml file, the header looked like this:

In a test file, I was reading the file bytes and decoding the data as UTF-8 (not realizing the header in this file was utf-16) to create a string.

byte[] data = Files.readAllBytes(Paths.get(path));
String dataString = new String(data, "UTF-8");

When I tried to deserialize this string into an object, I was seeing the same error:

javax.xml.stream.XMLStreamException: ParseError at [row,col]:[1,1]
Message: Content is not allowed in prolog.

When I updated the second line to

String dataString = new String(data, "UTF-16");

I was able to deserialize the object just fine. So as Romain had noted above, the encodings need to match.