It's not foolproof but it's probably the easiest and doesn't rely on any external data. Like all decent formats, GZip too begins with a magic number which can be quickly checked without reading the entire stream.
public static InputStream decompressStream(InputStream input) {
PushbackInputStream pb = new PushbackInputStream( input, 2 ); //we need a pushbackstream to look ahead
byte [] signature = new byte[2];
int len = pb.read( signature ); //read the signature
pb.unread( signature, 0, len ); //push back the signature to the stream
if( signature[ 0 ] == (byte) 0x1f && signature[ 1 ] == (byte) 0x8b ) //check if matches standard gzip magic number
return new GZIPInputStream( pb );
else
return pb;
}
(Source for the magic number: GZip file format specification)
Update: I've just dicovered that there is also a constant called GZIP_MAGIC
in GZipInputStream
which contains this value, so if you really want to, you can use the lower two bytes of it.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…