JVM property -Dfile.encoding=UTF8 or UTF-8?

If, running an Oracle HotSpot JDK 1.7.x, on a Linux platform where your locale suggests UTF-8 (e.g. LANG=en_US.utf8), if you don't set it on the command-line with -Dfile.encoding, the JDK will default file.encoding and the default Charset like this:

System.out.println(String.format("file.encoding: %s", System.getProperty("file.encoding")));
System.out.println(String.format("defaultCharset: %s", Charset.defaultCharset().name()));

... yields:

file.encoding: UTF-8
defaultCharset: UTF-8

... suggesting the default is UTF-8 on such a platform.

Additionally, if java.nio.charset.Charset.defaultCharset() finds file.encoding not-set, it looks for java.nio.charset.Charset.forName("UTF-8"), suggesting it prefers that string, although it is well-aliased, so "UTF8" will also work fine.

If you run the same program on the same platform with java -Dfile.encoding=UTF8, without the hypen, it yields:

file.encoding: UTF8
defaultCharset: UTF-8

... noting that the default charset has been canonicalized from UTF8 to UTF-8.

It will be:

UTF8

See here for the definitions.

Both UTF8 and UTF-8 work for me.