title: Low memory writing/reading with Apache POI
body: <p>I'm trying to write a pretty large XLSX file (4M+ cells) and I'm having some memory issues.</p>
  
  <p>I can't use SXSSF since I also need to read the existing cells in the template.</p>
  
  <p>Is there anything I can do to reduce the memory footprint?<br>
  Perhaps combine streaming reading and streaming writing?</p>