On Tue, 14 Aug 2001, Alex Garrett wrote:
> Forgive me if this is the wrong list to post to, but since it's a
> source related question (as opposed to a use question) I thought this
> list would be appropriate for my question.
>
> I'm reading through the source code and trying to understand the
> whole startup process -- how org.apache.catalina.startup.Catalina
> gets everything up and running. Unfortunately, I'm at loggerheads on
> one particular point. When the default server.xml file is parsed and
> the "examples" context is created, there are some sample tags like
> <Environment/> <Resource/> <Parameter/> and <Ejb/>. I realise that
> these tags correspond to classes in the org.apache.catalina.deploy
> package and that the classes are added to the StandardContext and
> accessed through various find methods.
>
Yes, that's right.
> Reading through the servlet spec (2.3pfd) it seems to me the purpose
> of these tags is to clue the web app as to what J2EE resources it has
> available. For example, the <ejb-ref/> tag provides the web app with
> the name (among other things) of an EJB so it can get a naming
> context and look up the EJB. Is this right?
>
Yes. The place to look for information about how an application uses this
stuff is in the J2EE Platform Specification (down near the bottom):
http://java.sun.com/j2ee/download.html
In particular, look at Chapter 5: "Naming".
The intent of the JNDI support in Tomcat 4 is to provide a compatible
environment for accessing <env-entry>, <resource-ref>, and
<resource-env-ref> values in Tomcat stand alone -- i.e. everything except
EJBs -- in a fashion that is identical to what you use on J2EE
servers. See below for more.
> Here's where I'm lost. I can't find any methods in
> javax.servlet.ServletContext that would provide access to the
> ContextEjbs (or any of the other deploy classes). In other words,
> StandardContext has the findEjb(String) method, but I don't see how
> javax.servlet.ServletContext or
> org.apache.catalina.core.ApplicationContext is able to access these
> deploy elements.
>
> Or have I completely misunderstood the purpose of the <Environment/>
> <Resource/> <Parameter/> and <Ejb/> tags? In any respect, I'd greatly
> appreciate a good dollop of enlightenment.
>
Let's say that what you want to do is access a connection pool (i.e. an
implementation of javax.sql.DataSource) as you are building a web app on
Tomcat 4, and you want to use exactly the same code that you will use when
the app is deployed on a J2EE server -- something like this:
Context initialContext = new InitialContext();
DataSource ds = (DataSource)
initialContext.lookup("java:comp/env/jdbc/EmployeeAppDB");
Connection conn = ds.getConnection();
... use this Connection ...
conn.close(); // Return connection to the pool
Now, in your application's web.xml, you declare a reference to this
connection pool, but without details:
<resource-env-ref>
<resource-env-ref-name>jdbc/EmployeeAppDb</resource-env-ref-name>
<resource-env-ref-type>javax.sql.DataSource</resource-env-ref-type>
</resource-env-ref>
The actual linkage of this connection pool to a "real" database happens
inside Tomcat 4's "server.xml" file -- see the declaration of the
"/examples" context.
> Thanks,
> Alex
>
>
Craig
