On 10/6/2010 8:10 AM, Jon Svede wrote:
I am willing to take stab at implementing this. I think I can do the properties
file part on my own based on what you've provided below. In this case, I assume
it will search for a specific file name? Or should it be something like a -D
argument passed in? Or maybe both? (a default file name and property to
override it?)
A system property set via -D is OK for a start. Let's stick to the name
"poi.udf.properties".
The error message for unknown functions sounds a little more involved, can you
give me some ideas of where to look to understand the intricacies?
It requires some research. I will post my ideas later, when I have a
minute to look into it.
Yegor
Jon
----- Original Message ----
From: Yegor Kozlov<[email protected]>
To: [email protected]
Sent: Tue, October 5, 2010 7:02:19 AM
Subject: Re: how to add functions to POI
As far as patching it, I don't think it *needs* a patch. One suggestion
might
be that when POI encounters a custom function and it throws an exception, the
comments of the exception point users to the UDFFinder docs.
This sounds like a good idea. If the formula evaluator stumbles on an unknown
function then the exception should suggest a workaround with UDF.
There can be tricky details - we need to tell unknown defined names from unknown
functions, this detection should work transparently for .xls and .xlsx formats,
etc. But anyway, I like the idea.
Your idea with configuration of UDFs also makes sense but I don't want to make
it too complicated. POI does not depend on Spring and I don't think we will add
a new dependency just for configuration of UDFs. So, Java properties is the way
to go.
In current implementation if UDFFinder is not specified then a default instance
is used, see UDFFinder.java:
public static final UDFFinder DEFAULT = new
AggregatingUDFFinder(AnalysisToolPak.instance);
I think it should be re-written into something like this
public static final UDFFinder DEFAULT = new
AggregatingUDFFinder.getInstance();
where getInstance() will search for a configuration file (system property or
classpath) and programmatically register UDFs, just like in the test case.
This way future versions of POI will be compatible with existing user code. If
support for custom VBA functions is needed then all user needs to do is to
implement the VBA code as FreeRefFunction and register it in the configuration
file.
Yegor
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