private String getExtension(String fileName) {
		if (fileName == null) {
            return null;
        }

		String ext = null;
		int i = fileName.lastIndexOf('.');

		if (i > 0 && i < fileName.length() - 1) {
			ext = fileName.substring(i + 1).toLowerCase();
		}
		return ext;
	}
private String getExtension ( String fileName ) { if ( fileName == null ) { return null ; } String ext = null ; int i = fileName . lastIndexOf ( '.' ) ; if ( i > 0 && i < fileName . length ( ) - 1 ) { ext = fileName . substring ( i + 1 ) . toLowerCase ( ) ; } return ext ; }
Return the extension of the filename

@param fileName
that should be inputed
@return file extension or null