I am a little new to J2EE. I have a EJB3 project and I want to run a class on application start-up, how can I do that?
I know in EJB3.1 I can use #startup and #singleton unfortunately that is not a option and I have to use EJb3 and java 5. I have done some research and there were a few solutions but I have been unable to make it work.
WebSphere Application Server version 6.1 does not support EJB3 with a standard installation. You also need to have a feature pack for EJB 3.0 installed.
See this information on the IBM site.
If this is not your issue you should update your question with more detail of what goes wrong.
Your only options prior to WebSphere 8 (with EJB 3.1 support) are:
WebSphere startup beans. These are a programming model extension
Package a WAR with the application, and use a ServletContextListener to initialize state used by the EJBs.
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How to EJB 3.1 Deployment in Tomcat 5.5.x
Blockquote
Any buddy please help me i have an web space with apache tomcat 5.0 jsp 2.0 and jvm 1.6
and i want to use ejb in my project so please tell me what should i do that i can use ejb 3.1 in my web space which have these resources listed below
i) Tomcat - 5.5.xSupport
ii)JDK - 1.6.x Support
iii)JSP/servlet - 2.0 Support
so how can i use EJB with web application with this available resources i mean what should i do to these things
Please Help me...!!!
It's not possible, go download JBoss AS or GlassFish.
Tomcat implements just the web container part of Java EE
It's definitely possible and in some cases I prefer the option of using a lightweight container instead of a more heavy weight application server. Having said this though the version of Tomcat your using is too old and won't work anyway without some serious messing about with the container (changing some JARs that come preinstalled with Tomcat), even with that I'm not sure it will work.
As Bozho says, try OpnEJB, but go for JBoss or Glassfish if you can. Tomcat is a JSP container and therefore not meant to this kind of use. EJB run on Application servers.
Does Tomcat 7 has the EJB implementation to allow create queues and deploy MDB listeners?
No, it doesn't. It only implements the JSP/Servlet API out the box (JSR-245 and JSR-315).
You can however use OpenEJB to enrich Tomcat with (limited) EJB support, including MDBs.
No, Tomcat is a servlet container, not a complete Java EE server, it has no EJB support on board.
There's a rich choice of open/free full Java EE servers available, check out Glassfish, JBoss, Geronimo or Jonas. And I'm probably forgetting several others.
On the Tomcat FAQ it says: "Tomcat is not an EJB server. Tomcat is not a full J2EE server."
But if I:
use Spring to supply an application context
annotate my entities with JPA
annotations (and use Hibernate as a
JPA provider)
configure C3P0 as a connection pooling data
source
annotate my service methods
with #Transactional (and use Atomikos
as JTA provider)
Use JAXB for marshalling and unmarshalling
and possibly add my own JNDI capability
then don't I effectively have a Java EE application server? And then aren't my beans EJBs? Or is there some other defining characteristic?
What is it that a Java EE compliant app server gives you that you can't easily/readily get from Tomcat with some 3rd party subsystems?
EJBs are JavaEE components that conform to the javax.ejb API.
JavaEE is a collection of APIs, you don't need to use all of them.
Tomcat is a "partial" JavaEE server, in that it only implements some of the JavaEE APIs, such as Servlets and JNDI. It doesn't implement e.g. EJB and JMS, so it's not a full JavaEE implementation.
If you added some additional bits and pieces (e.g. OpenEJB, HornetQ), you'd add the missing parts, and you'd end up with a full JavaEE server. But out of the box, Tomcat isn't that, and doesn't try to be.
But if I add (...) then don't I effectively have a Java EE application server? And then aren't my beans EJBs? Or is there some other defining characteristic?
No, you don't have a Java EE application server, a full-fledged Java EE application server is more than Tomcat + Spring + a standalone Transaction Manager. And even if you add a JMS provider and an EJB container, you still won't have a Java EE server. The glue between all parts is IMO important and is part of the added value of a Java EE container.
Regarding EJBs, the EJB specification is much more than JPA and specifices also Session Beans and Message Driven Beans (actually, I don't really consider JPA Entities as EJBs even if JPA is part of the EJB 3.0 specification in Java EE 5 for historical reasons - which is not true anymore in Java EE 6, JPA 2.0 and EJB 3.1 are separate specifications).
I should also mention that a Spring bean annotated with #Transactional is not equivalent to a Session Bean. A Java EE container can do more things with Session Beans (see below). You may not need them though but still, they are not strictly equivalent.
Last thing, Java EE containers implement a standard, the Spring container does not, it is proprietary.
What is it that a Java EE compliant app server gives you that you can't easily/readily get from Tomcat with some 3rd party subsystems?
As I said, I think that the "glue" is a part of the added value and highly contributes to the robustness of the whole. Then, ewernli's answer underlined very well what is difficult to achieve. I'd just add:
Clustering and Fail-over (to achieve fault-tolerance)
Administration facilities
Yes, a good Java EE server will do pretty neat things to improve fault tolerance (clustering of connection pools, JNDI tree, JMS destinations, automatic retry with idempotent beans, smart EJB clients, transaction recovery, migration of services, etc). For "mission critical" applications - the vast majority are not - this is important. And in such cases, libraries on top of the Servlet API are IMO not a replacement.
1) You're confusing JPA entities with EJBs. While JPA belongs to the EJB3 specification, it was always meant to be a standalone technology.
2) EJBs are: stateless beans, stateful beans and message driven beans. While each of these functionalities can easily be achieved using spring, spring just does not use this terminology. In Spring, you don't have POJO + "magic" as in EJBs, in Spring it's POJO + your own configuration (which sometimes feels like magic, too). The main difference is that spring does more and the application server does less, which is why a spring app is happy with a tomcat while an ejb3 app needs a 'real' application server.
In my opinion, 90% of applications can be deployed using spring + tomcat, ejb3 is rarely needed.
Indeed, if you put enough effort you can almost turn Tomcat/Spring into a full-fledged heavyweight application server :) You could even embed a portable EJB3 container...
What is it that a Java EE compliant app
server gives you that you can't
easily/readily get from Tomcat with
some 3rd party subsystems?
There are still a few features that are hard to get with 3rd party modules:
stateful session beans (SFSB)
extended persistence context
application client container / java web start
clustering depending on the app. server
CORBA interoperability
JCA integration ~
remoting ~
container-managed transactions ~
decent management of distributed transactions (e.g. recover heuristic tx)
Entries with ~ are also supported by Spring, but not so trivially, at least to my best knowledge.
A few more details in this answer: EJB vs Spring
Outside of the strict definition of what is and isn't an EJB, you're adding a lot of stuff to Tomcat. Even if what you have is an EJB server, it's not really plain Tomcat anymore.
The FAQ is correct: Tomcat is not an EJB server. However, it can be that or many other things if you pile on enough extra libraries and code.
An EJB implementation would be a bean written and packaged to run on any compliant EJB server. If you do what you describe, it may work, but it won't be portable to another vendor's application server.
So EJB is a standard that adheres to a specific specification and is therefore portable.
In practice many EJB's are not fully compliant or application server neutral. However, in the main they are, so the small incompatibilities would be much easier to fix if you changed application server vendors than attempting to move the architecture you described to a GlassFish, JBoss or Weblogic server.
EDIT: In response to your comment you would not have an EJB appropriately annotated and/or configured via XML in such a way that code that accessed it in EJB compliant ways would be able to use it without changes.
There are two angles to your comment. One is what functionality would you lose deploying on a JBoss or any of the others instead of Tomcat? Likely nothing, if you brought along all of the frameworks you relied on. However, if you wanted to move your code to Weblogic, for example, to use some of its features, then your code would need some likely significant changes to keep up.
I am not saying that you cannot replicate all EJB functionality (certainly the subset you care about) via other means, just that it is not the spec, and therefore not implementation independent.
then don't I effectively have a Java EE
application server? And then aren't my
beans EJB's? Or is there some other
defining characteristic?
Quick answer EJBs actually have to follow a Java EE specification. Tomcat is a Java EE container not an app server.
What is it that a Java EE compliant app
server gives you that you can't
easily/readily get from Tomcat with
some 3rd party subsystems?
Quick answer to your second question. In your case most likely nothing.
EJBs tend to be really heavy objects and people ended up using them to solve problems when they were essentially overkill. Frameworks like Spring were created to solve those problems without using EJBs. I think the first book where Spring was introduced was even called "J2EE development without EJB."
Right now I am using a web-server which does not contain EJB container. If my application needs EJB container, how could I add one?
Do you really mean into? If yes, then maybe have a look at OpenEJB (the EJB Container implementation for Apache Geronimo). But I can't say that it's widely used.
Actually, why not just replacing your servlet container with a full Java EE server if you need EJBs, I don't get it, something like JBoss AS or GlassFish.
OpenEJB and EasyBeans are open-source EJB containers that can be dropped into Tomcat or other servers / applications.
But, you should describing what you need this for... because if you need EJBs specifically, you're probably better off going with a full app server (JBoss, Glassfish, Weblogic, etc.). If you're just using it for persistence, you're probably better off using some other persistence technology (Hibernate, iBatis, etc.).
JBoss is an open source J2EE server. So if for some reason you can't just use it, you could take the EJB container and graft it into something else. Probably not a small job.
Too litte information on your architecture to give a decent answer.
Anyway chances are good you already apache as web server, you can simply connect using mod_jk to the embeddd tomcat in jboss.
This configuration will use the Apache JServ Protocol (AJP) for communication between Apache and Tomcat.
A description on which config files you have to fiddle about is here