title: Spring Outbound SFTP integration streaming
body: <p>We are developing a spring batch application which is going to process "big" files in the future. To maintain a low memory signature we use spring batch on the smallest possible chunks of these files.
  After processing, we want to write a result back to <code>SFTP</code>, which also happens per chunk of the input file.</p>
  
  <p>The current approach is as follows:</p>
  
  <p><code>StepExecutionListener.before()</code>: we send a message to the <code>SftpOutboundAdapter</code> with <code>FileExistsMode.REPLACE</code> and empty payload to create an empty file (with <code>.writing</code>)</p>
  
  <p><code>Reader</code>: will read the input file</p>
  
  <p><code>Processor</code>: will enhance the input with the results and return a list of string</p>
  
  <p><code>Writer</code>: will send the list of strings to another <code>SftpOutboundAdapter</code> with <code>FileExistsMode.APPEND</code></p>
  
  <p><code>StepExecutionListener.after()</code>: In case the execution as successful we will rename the file to remove the <code>.writing</code> suffix.</p>
  
  <p>Now I saw that there are <code>Streaming Inbound Adapters</code> but I could not find <code>Streaming Outbound Adapters</code>. 
  Is this really the only/best way to solve it by append? Or is it possible to stream the file content?</p>