Why do we need separate Remote and Local interfaces for EJB 3.0 session beans

Question

I was wondering why do we need separate Remote and Local intefaces for EJB 3.0 Session beans. I guess most of the time they would both be defining the same contract. Why cant I have a common interface and in my Bean I should just be able to say that I want this bean to be accessed remotely and/or locally.

thanks Vikas

Answer 1

This is what the EJB spec says:

The choice between the local and the remote programming model is a design decision that the Bean Provider makes when developing the enterprise bean.
While it is possible to provide both a remote client view and a local client view for an enterprise bean, more typically only one or the other will be provided.

JSR220 Chapter 3

So when writing a bean think about who is the client, it's very unlikely that a local client will need the same methods or even the same bean that a remote one.

Answer 2

I don't agree that at design time remote and local should be treated as trivially inter-changable.

First, there are overheads in remote invocation, so when designing remote interfaces you need to consider carefully whether you've got the granularity and parameter sizes right. So a reminder this is going to be comparatively expensive is helpful as a designer.

Also, Given that remote interfaces parameters are passed by value and local interface parameters are passed by reference there are fundamental semantic differences between the two cases hence you might choose to design the two interfaces differently.