title: Get length of HSSFWorkbook
body: <p>How I can get file size of Apache's POI <code>HSSFWorkbook</code>? </p>
  
  <p>I have code like </p>
  
  <pre><code>// inside Servlet
  OutputStream out = response.getOutputStream();
  hSSFWorkbook.write(out);
  </code></pre>
  
  <p>And I want to add <code>Content-Length</code> header to response.</p>