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From "Frank W. Zammetti" <fzli...@omnytex.com>
Subject Re: DataSource and initialContext.lookup("java:comp/env")
Date Sun, 07 Nov 2004 04:35:34 GMT
I'll give it a shot...

All JNDI resource lookups occur relative to some context.  The code you 
posted first gets the default initial context, then looks for a resource 
named "java:comp/env" relative to that default context.  It then gets a 
reference to a DataSource that exists within the context "jdbc/wms" 
relative to "java:comp/env"

You can ROUGHLY think of this the same way you do URLs... in a sense, 
the "java:comp/env" might be something like www.apache.org.  That gives 
you a starting context.  Then if you want to retrieve a particular file 
in that domain, you look it up relative to the domain (i.e., 
www.apache.org/tomcat.htm).

Same thing here... There is a hierarchy of JNDI resources, a tree 
structure, that has an initial context as the root.  You then are in a 
sense constructing a path to your DataSource, and it might look 
something like /initial_context/java:comp/env/jdbc/wms (not exactly, but 
you get the idea).

Does that help any?

-- 
Frank W. Zammetti
Founder and Chief Software Architect
Omnytex Technologies
http://www.omnytex.com

Eric Wulff wrote:
> I just returned from working on a tutorial at sun which I was inspired
> to go over based on my lack of understanding of the code snippet
> below.  I'm trying to fully understand what's going on.  Docs state
> that the code...
> 
> initialContext.lookup("java:comp/env") 
> 
> returns a named object.  Best I can tell is that this is a reference
> to a starting point in my directory... or something like that.  Is
> anyone willing to explain what initialContext.lookup() fundamentally
> takes care of when called?
> 
> Context initialContext = new InitialContext();
> Context context = (Context) initialContext.lookup("java:comp/env");
> DataSource dataSource = (DataSource) context.lookup("jdbc/wms");
> 
> thx
> Eric
> 
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