包头经常用两个字节压缩bcd码来表示

打包，如果338字节，转换成十进制数00x01,0x52

/**
 * function:2 hex byte[] to int,use pack
 * @param  len
 * @return  2 hex byte[]
 */
public static byte[] convertLen2HexByte(int len) {
    byte[] lenByte = new byte[2];
    String hexLen = Integer.toHexString(len);
    //奇数前补0
    hexLen = (hexLen.length() & 1) == 1 ? "0" + hexLen : hexLen;
    lenByte = convertHexStrToByteArray(hexLen);
    return lenByte;
}

/**
 * 将十六进制字符串转换成字节数组
 *
 * @param srcHex
 *            十六进制字符串
 * @return 字节数组
 */
public static byte[] convertHexStrToByteArray(String srcHex) {
    byte[] retByteArray = new byte[srcHex.length() / 2];
    byte tmpByte;
    String sDecode;
    for (int i = 0; i < srcHex.length() / 2; i++) {
        sDecode = "0x" + srcHex.substring(2 * i, 2 * i + 2);
        tmpByte = Integer.decode(sDecode).byteValue();
        retByteArray[i] = tmpByte;
    }
    return retByteArray;
}

/**
 * function:2 hex byte[] to int, use unpack
 * @param srcByteArray 2 hex byte[]
 * @return len
 */
public static int convert2HexByte2ToLen(byte[] srcByteArray) {
    if (srcByteArray == null)
        return -1;
    if (srcByteArray.length != 2)
        return -1;
    int firstByteHigh =  ((srcByteArray[0] >> 4)&0x0f);
    int firstByteLower = (srcByteArray[0] & 0x0F);
    int secondByteHigh =  ((srcByteArray[1] >> 4)&0x0f);
    int secondByteLower =  (srcByteArray[1] & 0x0F);
    return firstByteHigh*16*16*16 + firstByteLower * 16*16 + secondByteHigh * 16 + secondByteLower;
}