How do I retrieve image saved as a blob from oracle database please kindly help out.
with a select statement.
or you can go for hibernate, jpa, ...
which has ... nothing at all to do with being a servlet or not. you are simply calling a select statement.
again: what you need to know for this is basic jdbc, jpa, hibernate, or any other persistence framework.
In the example linked to by mutago, it's basic jdbc. A suggestion, don't study from RoseIndia. even though the site has been around for quite a while, it has some very huge flaws:
it's better to check the official tutorials provided by Oracle. they're kept up to date, and corrected when an error is found.