Java EE (Java Enterprise Edition) General Discussion

Refer
http://www.onjava.com/pub/a/onjava/2005/06/29/spring-ejb3.html

Sorry, I mean EJB2.1, not EJB3.0.

Spring and EJB are compared in terms of persistence. Spring (which uses Hibernate for persistence) is lightweight compared to EJB. There are other features like transaction management, scalability which could be compared. The basis of all these articles is "To EJB or not to EJB"... an attempt to provide an alternative to the bulkiness and complexity of EJB. EJB 3.0 is a promising specification which incorporates some of the features to make it lightweight. Read the article in that reply, if you are interested.

Because Spring came into being because its original developer found EJBs too complex and heavyweight to be useful. Spring is a framework that makes it possible to do JEE without EJBs.
This is incorrect. JEE includes JDBC, JSP, JMS, JTA, JNDI and a host of other technologies besides EJBs. It's possible to be a JEE application without EJBs.

The EJB specification is just that - a specification for a particular technology under JEE.
Correct.
You can remote to EJBs if you wish, but you don't have to write EJBs of your own. Spring almost treats EJBs as legacy code, like mainframes.
See above.
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I think their scopes are totally different. It still is strange to compare them to me.
The EJB is one of all specifications of J2EE. Spring is not the specification of J2EE. Spring has its own specifications as a framework to glue all specifications including EJBs of J2EE to provide the J2EE services. Am I right?

You're right - Spring is more encompassing than EJBs.
That's correct. There's no specification for Spring - it's the brainchild of Rod Johnson and the team that's coalesced around him. Spring can glue EJBs into an app and more besides.

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You are right. All those articles are aimed at "to EJB or not to EJB".

It seems that the POJOs in Spring in J2EE replaces the EJBs in J2EE.
If it is true, why couldn't it be the POJOs in J2EE without Spring?

EJBs in J2EE environment use JTA, JDBC, JMS, and so on.
POJOs in Spring in J2EE environment use JTS, JDBC, JMS, and so on.
POJOs in J2EE environment use JTS, JDBC, JMS, and so on.

What is the difference among three ways above to implement the business logic to provide the enterprise services?

Thank you for your guiding.

Can be, but what do you lose by doing this?
EJBs have the added benefit of having the container manage their life cycle.
Add in that Spring encourages the use of interfaces and externalizes configuration in XML files. I think Spring's use of singletons is meaningful here. It's tied in with the use of interfaces.

There's a lot added to the Spring framework classes that does things for you behind the scenes. That's what's different.
But in this case you either end up hardwiring dependencies or externalizing them yourself.
See above. If you do POJOs yourself, you're writing all that framework code. You can. It's your choice whether to do it or not.

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Thank you very much.

If I write an BMP bean + JDBC API in J2EE, a POJO + JDBC API in Spring in J2EE, and a POJO + JDBC API in J2EE, could you please guide me what the real different things that needed to be done are among them?

Thank you.

I could do without the bold.

I'm not sure exactly what you're looking for below. I'm certainly not going to give you full examples of each. But here goes:
You'll have to write the JDBC code in your entity bean that persists the entity bean attributes into tables. You'll need CRUD operations for your entity.
If I had to persist a POJO named Foo, I'd start with a FooDao interface:

public interface FooDao
{
   public Foo findById(Long id);
   public List findAll();
   public void saveOrUpdate(Foo foo);
   public void delete(Foo foo);
};

My Spring implementation of the FooDao would extend JdbcTemplate and use all the machinery it made available to me. I'd have to write a dao application context XML to wire it together with its connection, etc.
Same as above, without the JdbcTemplate to help me.

could you please guide me what the real

different things that needed to be done are among

them?

Thank you.
Is that what you had in mind?

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