Yegor,
That example is very straightforward, thanks for pointing me to it.
Additionally, I would like to contribute some docs on this because I think this
is a really nice feature. Are there instructions somewhere I can reference for
adding such a contribution?
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.
I can see a way to add to it, though. This example works well when you have a
single workbook with a small set of functions that need to be converted. But
what if you have an application built on POI that has a number of workbooks
with
a number of custom functions? This declarative approach might be cumbersome
(but certainly workable, so I am not criticizing).
My suggestion would be to provide some ability to do this through
configuration. The code snippet:
UDFFinder udff1 = new DefaultUDFFinder(new String[] { "myFunc",
}, new
FreeRefFunction[] { new MyFunc(), }); UDFFinder udff2 = new
DefaultUDFFinder(new String[] { "myFunc2", }, new
FreeRefFunction[] { new
MyFunc2(), }); This is basically registration, not unlike registering beans
with
Spring or even something simple like a properties file. If this could be moved
from code to a configuration I think it would make coding for these workbooks
with custom functions easier (though on the other hand there is an argument to
be made for keeping it as it is because this makes it declarative that a given
workbook has custom functions). Another benefit of going the configuration
route is that a developer could write the function, add it to a file and
basically forget about it because their POI instance would have it globally.
On my project, we don't have an immediate need for this functionality, but
maybe
others do?
So my idea would be something like the following:
UserDefinedFunctions.xml:
<beans>
<bean id="myFunc" class="com.mycompany.my.project.MyFunction"/>
<bean id=="myFunc2" class="com.mycompany.my.project.MyFunction2"/>
</beans>
or
UserDefinedFunctions.properties
myFunc=com.mycompany.my.project.MyFunction
myFunc2=com.mycompany.my.project.MyFunction2
If you prefer not to use Spring. There are probably other ways to achieve this
part, these are just examples.
In the application code:
Workbook workbook = WorkbookFactory.create( "path/to/target/workbook.xls",
"path/to/UserDefinedFunctions.xml" ) ;
Another way would be to have POI look in the classpath for a specific file; if
it exists, POI loads the functions defined. Then in the code there is no
reference at all to this file (though again, it might make it more confusing).
I realize that this is semantic, users of the API could easily add this
themselves. I like the idea of not having to code the registration myself.
Anyway, hopefully this doesn't come off as a criticism because I am definitely
not criticizing, this is great functionality as it is. I've used POI over the
years and I think very highly of it. Please let me know if I can be of
assistance.
Sincerely,
Jon
----- Original Message ----
From: Yegor Kozlov <[email protected]>
To: [email protected]
Sent: Mon, October 4, 2010 2:07:12 AM
Subject: Re: how to add functions to POI
> If after reading the code and the docs I can see how I might be of assistance
I
> will do as you suggested. Outside of the test case, is this feature
> documented? I don't recall reading about this.
UDF is not well documented, all available bits of documentation are those in
the
source code and in Bugzilla.
Perhaps, a good contribution would be an example how to use the UDF API.
Patches are welcome.
Yegor
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