B转换KB，MB，GB的方法

public static String formetFileSize(long fileS) {

DecimalFormat df = new DecimalFormat("#.0");
String fileSizeString = "";
if (fileS < 1024) {
fileSizeString = df.format((double) fileS) + "B";
} else if (fileS < 1048576) {
fileSizeString = df.format((double) fileS / 1024) + "K";
} else if (fileS < 1073741824) {
fileSizeString = df.format((double) fileS / 1048576) + "M";
} else {
fileSizeString = df.format((double) fileS / 1073741824) + "G";
}
return fileSizeString;
}