code: public BoxRequestsFile.DownloadFile getDownloadRequest(OutputStream outputStream, String fileId) {
              BoxRequestsFile.DownloadFile request = new BoxRequestsFile.DownloadFile(fileId, outputStream, getFileDownloadUrl(fileId),mSession);
              return request;
      }
docs: Gets a request that downloads the given file to the provided outputStream. Developer is responsible for closing the outputStream provided.
  
  @param outputStream outputStream to write file contents to.
  @param fileId the file id to download.
  @return  request to download a file to an output stream