Cannot send/receive file as a stream when uploading/downloading from API

Hi,

Background: We are currently trying the Adobe Sign APIs inside our java based application(a cloud ERP application). We have been trying to be efficient in memory and storage consumption when calling upload/download document APIs.

Our requirement: is to pass the file as a stream(as an inputstream) when creating/uploading a Transient Document(also, get the file as a stream when downloading the signed document) from the API.

What we tried:

1. with the Java SDK and It seems

• For uploading a Transient Document: It is required to save it on the disk - which then consumes storage and memory(when reading back)
• For downloading: Return the file as a byte array - which is in memory and also consumes more memory when converting to a stream.

2. with our own way, creating the HTTP request, adding an input stream for the "file" part in the multipart body. 

• request failed

We saw that the API documentation mentions file stream.

Question: What does file stream really mean here? Is there a way we can achieve our requirements?

Appreciate your comments.

Thanks!