differences in detail

[shanmukeshwar shastri]

Hi,
I have few questions to forward you, regarding EJB.I read the points u gave, but pretty confused.Can u give me a clear picture some good examples regarding EJB.
Here are the questions
1)Difference between session and entity beans?
2)Difference between stateless and stateful session bean?
3)Difference between Entity bean-managed persistence and container-managed peristence?
4)Difference between fine-grained bean and coarse-grained bean?
5)What is freepool and session facade?
Help me with some real time examples in detail.Hope I am not troubling u.
regards,
Shastri

[Lasse Koskela]

First, welcome to the JavaRanch!

Originally posted by shanmukeshwar shastri:
I have few questions to forward you, regarding EJB.I read the points u gave, but pretty confused.

Umm. You read what points given by whom?

Originally posted by shanmukeshwar shastri:
Can u give me a clear picture some good examples regarding EJB.
Here are the questions
1)Difference between session and entity beans?
2)Difference between stateless and stateful session bean?
3)Difference between Entity bean-managed persistence and container-managed peristence?
4)Difference between fine-grained bean and coarse-grained bean?
5)What is freepool and session facade?

May I suggest starting by downloading and reading the free ebook, Mastering EJB II, which should give you an understanding about EJB fundamentals.
Here are brief answers to give you at least some idea:
1) Session beans represent business logic, i.e. what your application does, while entity beans represent business entities, i.e. what entities your business domain consists of.
2) Stateless session beans do not maintain client-specific state while stateful session beans do.
3) In BMP, you write the database access code yourself, in CMP the container does this for you.
4) Fine-grained beans gives its user access to pieces of data that are "smaller" than the ones a coarse-grained bean gives access to.
5) The "free pool" is a pool of bean instances that the EJB container maintains internally for improving performance. Session Facade is an EJB design pattern described here.

[Lasse Koskela]

Here are some examples for the difference between stateful and stateless session beans

// a stateless bean always does the same thing, regardless of
// previous method invocations (think static methods)
MyStateless bean = lookupMyStatelessBean();
System.out.println(bean.saySomething()); // prints "1"
System.out.println(bean.saySomething()); // prints "1"
System.out.println(bean.saySomething()); // prints "1"
bean.remove();
// a stateful bean holds state in between method calls
MyStateful bean = lookupMyStatefulBean();
System.out.println(bean.saySomething()); // prints "1"
System.out.println(bean.saySomething()); // prints "2"
System.out.println(bean.saySomething()); // prints "3"
bean.remove();

Here are some examples for the difference between coarse-grained and fine-grained entity beans:

// coarse-grained entity bean returns all data within a single data transfer object
Account account = lookupCoarseGrainedAccount(...);
AccountDTO data = account.getData();
String id = data.getId();
String name = data.getName();
double balance = data.getBalance();
// fine-grained entity bean returns each piece of data using a different 
// remote call (which are expensive as they go over the network)
Account account = lookupFineGrainedAccount(...);
String id = account.getId();
String name = account.getName();
double balance = account.getBalance();