Re: JNDI vs. web.xml
On Wed, 27 Oct 2010, markspace wrote:
I'm seeing a lot of discussion lately about using JNDI for "loose coupling"
and binding clients in applications.
May i ask where? I've had some thoughts on this rolling round in my head
for a year or so, but i didn't know anyone else cared.
I'm curious why JNDI is regarded as superior to just using configuration
parameters in something like a web.xml file.
To me it seems like servlet parameters in a web.xml file would work
exactly in the same was as JNDI look up. The servlet parameters are
injectable, there's a naming convention that has to be managed. (I.e.,
if your JNDI is "comp/env/jdbc/myDB", your init parameters could use a
similar convention). And over all the two technologies seem to do
Calling "classForName" on an init parameter isn't very difficult, though
it does require some work, and on the JNDI side there's a bunch on new
classes to manage, JNDI configuration to manage and new APIs to learn.
It looks a bit like a wash to me.
The big difference that springs to mind - assuming i've understood this
right - is that JNDI gives you objects, whereas init-params and
Class.forName gives you classes. JNDI lets you wire up an actual object
graph declarative-ishly, whereas if you're passing class names in to
components, the best each component can do is build an instance of that
class that isn't shared with anything else. There's no way to build object
For example, say you're writing the new Facebook, and you want to wire
several servlets to a common UserRegistry object. With JNDI, you set it up
and bind it somewhere, and the servlets can all get to it. How do you do
that with init-params? It's going to involve static variables somehow.
As you say, though, it's much more of a pain to work with JNDI than
env-entries. What we could do with is some sort of simple wrapper round
JNDI, so my servlet can go:
UserRegistry users = (UserRegistry) new JNDIHelper().resolveName("/org/newfacebook/UserRegistry");
And get what it needs.
The powers that are at work here are immensly strong, and extremely
difficult to comprehend. -- Pete