Detection of encoding of XML file with the StAX parser

Question

Hello!
I am using the StAX parser to read an XML file which can have different encodings.
I don't know how to detect the encoding before reading the file.
This is the way I instantiate the reader now:
XMLStreamReader xmlr = xmlif.createXMLStreamReader(new InputStreamReader (new FileInputStream(inputfile), "utf-8"));
Is there any way to make the reader detect the encoding with StAX? Is it possible detect the encoding with SAX or DOM?
Just paste some piece of code and you will help me a lot!
Thanks,
Lara

Answer 1

XML parsers are supposed to auto-detect the encoding of their inputs. The SAX and DOM parsers built into Java, as well as others like Xerces, do that. I don't know whether your StAX parser does, but it should. There is a standard procedure for determining the encoding that is described in the XML spec.
However if you have malformed XML that fails to declare its encoding properly, then none of those parsers will be able to fix that problem for you.
Here's the simplified rule as it applies to most files: if the XML file doesn't have a prolog, or if it's prolog doesn't specify an encoding, the parser will assume the file's encoding is UTF-8. If the XML file does have a prolog that specifies an encoding, the parser will assume that encoding.
Unfortunately it is common for people to write XML files that don't declare an encoding, but to forget to encode the file in UTF-8. Then you have a file that is actually encoded in (e.g.) Windows-1252, but the parser believes it is UTF-8, and this fails when there are non-ASCII characters in the document.