XSLT Error Reference
Content is not allowed in prolog
Error message
org.xml.sax.SAXParseException: Content is not allowed in prologThe XML parser found characters before the XML declaration or root element: usually a UTF-8 BOM, stray whitespace/text, or a file that is not XML at all (an HTML error page, for instance).
What it means
The prolog is everything before the root element. Only the XML declaration, comments, processing instructions and whitespace may appear there. Any other content — even a single invisible byte — triggers this error.
Common causes
- UTF-8 BOM (byte order mark). Files saved as “UTF-8 with BOM” start with the bytes
EF BB BF. Many Java parsers reject them when the document is served or concatenated carelessly. Save as UTF-8 without BOM. - Stray text before
<?xml— a leftover log line, a shell prompt, an HTML comment from a template engine. - The file is not XML at all. Classic case: your code fetched a URL and got an HTML error page (login redirect, 404, proxy error) and then fed it to the XML parser. The parser dies at character 1 of
<!DOCTYPE html>… or earlier. - Encoding mismatch — the declaration says
encoding="UTF-8"but the bytes are UTF-16, so the first bytes are unreadable.
How to fix it
- Inspect the first bytes with a hex viewer (
xxd file.xml | head -1) — a BOM shows asefbb bf. - If the XML comes over HTTP, log the raw response before parsing: is it actually XML?
- Re-save the file as UTF-8 without BOM and make sure nothing writes to the stream before the XML declaration.
- Paste the content into XSLT Playground — invisible junk becomes obvious when the parser points at line 1, column 1.