字符串转成KB，MB, GB

import java.text.DecimalFormat;

public class SizeUtil {

    public static String GetImageSize(String imageSize) {
        String size = "";
        if (imageSize != null && !"".equals(imageSize)) {
            long fileS = Long.parseLong(imageSize);
            DecimalFormat df = new DecimalFormat("#.00");
            if (fileS < 1024) {
                size = df.format((double) fileS) + "BT";
            } else if (fileS < 1048576) {
                size = df.format((double) fileS / 1024) + "KB";
            } else if (fileS < 1073741824) {
                size = df.format((double) fileS / 1048576) + "MB";
            } else {
                size = df.format((double) fileS / 1073741824) + "GB";
            }
        } else {
            size = "0BT";
        }
        return size;
    }
}