java 如何把byte转化为KB、MB、GB的方法

public static String getNetFileSizeDescription(long size) {
        StringBuffer bytes = new StringBuffer();
        DecimalFormat format = new DecimalFormat("###.0");
        if (size >= 1024 * 1024 * 1024) {
            double i = (size / (1024.0 * 1024.0 * 1024.0));
            bytes.append(format.format(i)).append("GB");
        }
        else if (size >= 1024 * 1024) {
            double i = (size / (1024.0 * 1024.0));
            bytes.append(format.format(i)).append("MB");
        }
        else if (size >= 1024) {
            double i = (size / (1024.0));
            bytes.append(format.format(i)).append("KB");
        }
        else if (size < 1024) {
            if (size <= 0) {
                bytes.append("0B");
            }
            else {
                bytes.append((int) size).append("B");
            }
        }
        return bytes.toString();
    }

import java.math.BigDecimal;
public class ByteUtil {

    public static final Integer KB_SIZE = 2 << 9;
    public static final Integer MB_SIZE = 2 << 19;
    public static final Integer GB_SIZE = 2 << 29;

    public static BigDecimal bytes2Unit(long bytes, Integer unit) {
        BigDecimal size = new BigDecimal(bytes);
        BigDecimal u = new BigDecimal(unit);
        return size.divide(u, 2, BigDecimal.ROUND_DOWN);
    }

    public static Long unit2Byte(BigDecimal decimal,Integer unit) {
         return decimal.multiply(BigDecimal.valueOf(unit)).longValue();
    }

    public static Long kb2Byte(BigDecimal decimal) {
        return decimal.multiply(BigDecimal.valueOf(KB_SIZE)).longValue();
    }

    public static Long mb2Byte(BigDecimal decimal) {
        return decimal.multiply(BigDecimal.valueOf(MB_SIZE)).longValue();
    }

    public static Long gb2Byte(BigDecimal decimal) {
        return decimal.multiply(BigDecimal.valueOf(GB_SIZE)).longValue();
    }

    public static BigDecimal bytes2Kb(long bytes) {
        return bytes2Unit(bytes,KB_SIZE);
    }

    public static BigDecimal bytes2Mb(long bytes) {
        return bytes2Unit(bytes,MB_SIZE);
    }

    public static BigDecimal bytes2Gb(long bytes) {
        return bytes2Unit(bytes,GB_SIZE);
    }
}