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Posted to dev@tomcat.apache.org by Alex Garrett <lj...@thinkpig.org> on 2001/08/14 20:52:46 UTC
ContextEjb & related deploy classes
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.
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?
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.
Thanks,
Alex
Re: ContextEjb & related deploy classes
Posted by "Craig R. McClanahan" <cr...@apache.org>.
On Tue, 14 Aug 2001, Alex Garrett wrote:
> Thanks for the help! I was still confused as to how the web app gets
> the information, but what you gave me pointed me to the
> StandardContext.createNamingContext() method and it all makes perfect
> sense, now.
>
> Incidentally, as I continue to try to understand the codebase, I'll
> probably have similar questions. I'll try to puzzle out the answers
> by reading the code, specs, and list archives, but lacking that, is
> this the appropriate place to ask questions about the source, or
> should that be confined to tomcat-user?
>
For qustions about Tomcat internals, you'll do better here.
And, if you volunteered to write up the answers as docs that can be
included with Tomcat, we'll be *very* motivated to answer those questions.
:-)
> Thanks again,
> Alex
>
Craig
> >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.
>
>
Re: ContextEjb & related deploy classes
Posted by Alex Garrett <lj...@thinkpig.org>.
Thanks for the help! I was still confused as to how the web app gets
the information, but what you gave me pointed me to the
StandardContext.createNamingContext() method and it all makes perfect
sense, now.
Incidentally, as I continue to try to understand the codebase, I'll
probably have similar questions. I'll try to puzzle out the answers
by reading the code, specs, and list archives, but lacking that, is
this the appropriate place to ask questions about the source, or
should that be confined to tomcat-user?
Thanks again,
Alex
>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.
Re: ContextEjb & related deploy classes
Posted by "Craig R. McClanahan" <cr...@apache.org>.
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