Morning Greg,

Whilst I have had a very good look through the javadocs, I am by no means an
expert so treat what I have to say with caution please. Having said that, I
do not think there is an existing method within the POI API that you can use
to transcode (convert) between an OpenXML file and a binary (BIFF8) file.
You could use POI to create such a method however by stepping through the
input workbook - an XSSFWorkbook in your case I would guess - and creating
analogous objects within an HSSFWorkbook for everything you find there; if
your workbooks are fairly simple then this could be the way to go but if
they are more complex then that could involve some work.

You do have other options however and the best one - at least to my mind -
would be OLE/COM. If you are working on a stand alone PC and have Office
2007 installed on that machine, then you can use OLE to control an instance
of the Excel application and 'ask' it to convert the files for you. There
are plenty of libraries you could use to accomplish this task but the only
one I have any experience with is the ole32 package of the Standard Widget
Toolkit. The SWT is part of the Eclispe IDE, can be downloaded separately
and I have found it quite easy to work with. In fact, if you choose to go
this way, let me know and I will forward a couple of classes that will allow
you to use Excel to convert between different file types. You do need to be
aware however that this approach does have problems; it is hard to trap and
handle errors for example. Still, I think this is the beast approach as you
are using the application created by the authors of the file formats
involved.

A slightly modified version of this would be to use Excel macros to perform
the conversions for you. It is possible to create a VBA macro that would
open a file and save it in a different format. If you have lots of files to
process, you could enter their names into the cells of a worksheet and have
the macro iterate through the cells opening each file and then re-saving it
in the appropriate format. Of course, this also depeneds upon your having
access to Office 2007. I have never done this but it would be a simple task
to use the macro recorder feature to prototype the code and then simply
tweak it to do what you require.

The third option is OpenOffice. It uses filters to handle different file
types and by specifying the filter the application should use, it is
possible to convert between different file types. Again, it is possible to
control OpenOffice from Java code through a clearly defined - though complex
- interface. Using this technique again depened upon having OpenOffice and
it's associated SDK installed. Furthermore, I would advise you to use either
Eclipse or Netbeans as you IDE as both have a plugin that make developing
UNO client applications far easier. As with OLE, I have code that I can let
you have to accomplish this task. In my experience, OpenOffice is fine with
all but the more complex spreadsheet files; for example, it has problems
handling OpenXML spreadsheets that contain embedded objects and I am certain
there will be other limitations. My only concern with this technique is that
I have not yet been able to find the specific filter for opening and openXML
based workbook even thgouhg I know that Calc can read such files.

Finally, there are on-line conversion services available. This would be, to
my mind, a last resort as you would have to send your files across the
internet to a third party; the security implications are obvious.

Hope this helps.

Yours

Mark B


Greg Inns wrote:
> 
> Use Case: read in an XLSX file, convert it, and write out an XLS file.
> 
> It looks like both the HSSFWorkbook and the XSSFWorkbook both implement
> the SS Workbook interface, but that's where it ends.  In my mind, it make
> sense to be able to construct a HSSFWorkbook from an XSSFWorkbook and visa
> versa, although I would expect there might be some lost information in
> former case.  
> 
> Am I missing something in the API documentation?  Or something else?
> 
> 
> 

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