title: Close Filehandle for Workbook (apache poi)
body: <p>I constructed a new Workbook using <code>WorkbookFactory.create(new File("path/to/xlsx"))</code>. However, when I try to edit the File in Excel after starting the application, I get an error message that the file is in use. Do I have to free the file up, and if so, how? (I could not find anything like <code>Workbook.close()</code> in the api docs) Or do I have to look in other places?  </p>
  
  <p>I have no clue where else to look; the application does not cause these issues with csv and for excel files I simply call the converter (xls => csv) which is the only difference.</p>
  
  <p>(I am using POI 3.8)</p>