I have a below class in which I am passing certain parameters through constructor and then using those parameters I am making one final byte array with proper format (header + data) as shown below:

public final class Frame {
  private final byte addressedCenter;
  private final byte version;
  private final Map<byte[], byte[]> keyDataHolder;
  private final long location;
  private final long locationFrom;
  private final long locationOrigin;
  private final byte partition;
  private final byte copy;

  public Frame(byte addressedCenter, byte version,
      Map<byte[], byte[]> keyDataHolder, long location, long locationFrom,
      long locationOrigin, byte partition, byte copy) {
    this.addressedCenter = addressedCenter;
    this.version = version;
    this.keyDataHolder = keyDataHolder;
    this.location = location;
    this.locationFrom = locationFrom;
    this.locationOrigin = locationOrigin;
    this.partition = partition;
    this.copy = copy;
  }

  public byte[] serialize() {
    // All of the data is embedded in a binary array with fixed maximum size 70000
    ByteBuffer byteBuffer = ByteBuffer.allocate(70000);
    byteBuffer.order(ByteOrder.BIG_ENDIAN);

    int numOfRecords = keyDataHolder.size();
    int bufferUsed = getBufferUsed(keyDataHolder); // 36 + dataSize + 1 + 1 + keyLength + 8 + 2;

    // header layout
    byteBuffer.put(addressedCenter); // byte
    byteBuffer.put(version); // byte
    byteBuffer.putInt(numOfRecords); // int
    byteBuffer.putInt(bufferUsed); // int
    byteBuffer.putLong(location); // long
    byteBuffer.putLong(locationFrom); // long
    byteBuffer.putLong(locationOrigin); // long
    byteBuffer.put(partition); // byte
    byteBuffer.put(copy); // byte

    // now the data layout
    for (Map.Entry<byte[], byte[]> entry : keyDataHolder.entrySet()) {
      byte keyType = 0;
      byte keyLength = (byte) entry.getKey().length;
      byte[] key = entry.getKey();
      byte[] data = entry.getValue();
      short dataSize = (short) data.length;
      
      ByteBuffer dataBuffer = ByteBuffer.wrap(data);
      long timestamp = 0;

      if (dataSize > 10) {
        timestamp = dataBuffer.getLong(2);              
      }       

      byteBuffer.put(keyType);
      byteBuffer.put(keyLength);
      byteBuffer.put(key);
      byteBuffer.putLong(timestamp);
      byteBuffer.putShort(dataSize);
      byteBuffer.put(data);
    }
    return byteBuffer.array();
  }
  
  private int getBufferUsed(final Map<byte[], byte[]> keyDataHolder) {
    int size = 36;
    for (Map.Entry<byte[], byte[]> entry : keyDataHolder.entrySet()) {
      size += 1 + 1 + 8 + 2;
      size += entry.getKey().length;
      size += entry.getValue().length;
    }
    return size;
  }  
}

I am opting for code review to see whether it can be improved in any way or any better way? As you can see right now, I am allocating ByteBuffer with predefined size of 70000. Maybe there is a better way by which I can allocate the size I am using while making ByteBuffer instead of using hardcoded 70000?