Hello, EJB-DEVELOPERS!
Sorry if you see this msg for the second time, I'm not sure
if it got to the list the first time, so reposting.. Plz excuse
for possible inconvenience.
Yesterday there was a letter on JSP-INTEREST, basically asking
"How to use EJB-s with JSP-s/Servlets. I'm not an expert in this area,
but I have written a reply to this letter. The more I read my own
reply the more doubts I have. Finally I decided to subscribe to
EJB-INTEREST and send my "essay" here to ask people more knowledgeable
in the EJB containers then I am to comment on my expectedly numerous
mistakes.
BTW, I've also got some questions there at the bottom of the letter.
I would feel _very obliged_ to hear answers to them too:
no kidding you would through fog off my eyes that has been long covering
them! Plz, HELP!
Okay, here goes the letter
==========================================================================
Hello Gerry!
Not an expert, just my two-penny! I'm a beginner with EJB too!
Gerry Scheetz <[EMAIL PROTECTED]> wrote:
GS> Some topics I have run across while surfing and my thoughts.
GS> ** Enterprise Java Beans - no in-house knowledge, so we would be learning
GS> from the ground up. Do we need a server?
Yup!
Here I'm going to write some rubbish, plz, experts, correct me!
Generally all the EJB containers may run in one of two ways:
1) EJB container run in the same jvm as the servlet container (then they
communicate locally.)
(requires tight integration between
EJB and web containers)
I guess that here it is enough to create initial
context with a zero-arg constructor:
new InitialContext();
and this is J2EE compliant.
These are the things you need to do to make
the ejb appear in your InitialContext:
Declare that you webapp uses the ejb,
this is like "declaring a variable" in a programming
language in your web.xml either:
- use a <ejb-ref> element
this implies using the whole heavy
and time-consuming marshalling machinery
- use a <ejb-local-ref> element
this implies skipping the whole
marshalling machinery and working directly
Then you should "assign a value" to the "variable",
bind a EJB home interface to the webapp's JNDI context.
You do it either
1a) - directly: you put a <ejb-link> element inside the <ejb-ref>,
or <ejb-local-ref> element
(I do not think this is a common scenario)
1b) - indirectly: you use some EJB+Web container specific way
(often via a web interface and/or via additional deployment
descriptors)
2) EJB container and web container run in different JVMs. They use tcp
to communicate.
(This allows web and EJB containers that were not pre-tuned for
each other still cooperate, but then it is 2.2 not 2.1)
The 2) section has two subsections:
2.1) EJB container and Web container are integrated closely enough.
All is J2EE compliant. This is much like 1) variant, only you
can not use <ejb-local-ref>, only <ejb-ref>
2.2) you have to create the InitialContext with
plenty of parameters (fill a HashMap and pass it to the
constructor).
This is not J2EE.
You create an InitialContext that
is almost completely independent of what the web container has
provided you with and it does have to initiate a new TCP
connection. (This may be as slow as creating a new database
connection, i guess)
GS> Are they tough to code?
Haven't tried it, but guess it should be a piece of cake :-)
GS> How to get info from there to JavaBean for use in JSP?
Here I'm a moron. Please, others, do correct me!
Still you may
** have a normal JavaBean interact with a Enterprise
Java Bean internally. Internally you create the
InitialContext, do the look-ups and all the stuff
You may use the Value object pattern in this case and
probably save some time and network bandwidth. Although
with 1a) variant the Value object pattern is not necessary.
** somewhere in the controller servlet (or in a jsp directly)
you create the initial context, do the lookup, get an instance
of remote (EJB 1.1 terminology) interface and bind it somewhere.
I guess the best is as a request attribute. Then it behaves
as a normal JavaBean and you may use it. I guess that especially
with 1a) variant this is a feasible solution
GS> I am open for suggestions. Actually what I would really like is a location
GS> online where I can research this a bit more.
Upps, let others help you with this :-)
- Anton
[EMAIL PROTECTED]
[EMAIL PROTECTED]
P.S.
Questions that I would like to hear answers too are:
- I just do not know if variant 2.1) actually happens in real life.
I just do not know if WAS and Weblogic are 1) or 2.1).
Plz, tell me!
(I'm sure that 1) exists, JBoss+Tomcat4.0.1 give an example
and that 2.2) exists, Resin may work in this fashion with
great many EJB containers)
- I know that if we download JBoss+Tomcat4.0.1 from jboss.org
it may all work and may be work in the 1) way.
I guess that Tomcat may well work as 2.2), I guess that
any web container will work 2.2)
The question is: are there any other ways to make Tomcat
run 1) then using the JBoss+Tomcat install?
Does Tomcat run in the 2.1) mode?
If not for both questions, then how can Tomcat be a reference
implementation while Servlet 2.3 requires JNDI app context
described in J2EE version 1.3
and it requires support for <ejb-ref> and <ejb-local-ref>?
- Can Resin be made run 1) or 2.1)? I guess the currently it
can not.
--------------------end-of-letter------------------------------
- Anton
===========================================================================
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