If a file can be saved in all kinds of databases?( I just know of ORACLE in this context). I asked this question because in case while developing the project, one doesn't know what database might be used in future.
I'd hope so, though I can't say for sure. Every RDBMS I've used can support CLOBS or BLOBs etc. (or LONG RAW on older Oracle versions). But I wouldn't claim to know about all possible DBs so I suggest you do some checking if you are concerned.
To use JCA adapter for reading a file (while taking it as a datasource), we need to specify the jdbc driver class in xxx-ds.xml.
You need to specify a "driver" - but would be a driver for the resource you are trying to access, so its not a JDBC driver it would be some kind of File System resource adapter.
if we don't use jdbc driver then I suppose we have to write the implemenation code for JCA resource adapter to read/write xml file.
Yes. Or do some Googling for one that someone else has written. I can't think of one off the top of my head.
If we write JCA resource adabtor then how do we configure it in xxx-ds.xml file?
That's covered in
JBoss's
docs