question: public static boolean isCompressed ( File file ) { InputStream fis = null ; try { if ( file . exists ( ) ) { fis = new FileInputStream ( file ) ; int mag1 = fis . read ( ) ; int mag2 = fis . read ( ) ; fis . close ( ) ; return selectCompressionProvider ( mag1 , mag2 ) != null ; } } catch ( IOException e ) { LOG . log ( Level . FINEST , "Error while checking if file " + file + " is compressed" , e ) ; return false ; } finally { SafeClose . close ( fis ) ; } return false ; }
target:  Is a file compressed? (the magic number in the first 2 bytes is used to detect the compression.