Injection at invocation time, not instantiation time

[bdecoste]

A customer is asking for injection to occur at invocation time, not bean instantiation time. This is a non issue for session beans as they are instantiated at invocation time, but it's an issue for Service beans that are instantiated at deploy time. Specifically the problem is if a @Service bean tries to inject @EJB(mappedName="xyz") and that bean is not yet deployed on another node, the @Service bean fails to deploy.

Another way to resolve this is not to instantiate Service beans until invocation time just like session beans.

Thoughts?

[bdecoste]

The problem with delaying instantation or injection is that the @Service bean may never be invoked - it could be some background service ...

God, I feel like Adrian talking to myself on the forums :-)

[cbredesen]

The case against this would be service beans that aren't interactive, but are background workers, and thus never invoked. So at what point do you deploy/inject those? The obvious answer is that you make those work like the current service beans (deployed at startup) but then how do you differentiate between the beans that are invoked and ones that are purely background ones?

[wolfc]

The service beans are also used for one time startup logic. These never get called.

[bdecoste]

There seems to be an echo in here. The more I think about it, the more I like the idea of doing injection based on an interceptor. The interceptor could be bound to constructors or to methods, so config would control when injection occurs.

[wolfc]

JSR 250 disallows for injection after construction. (See also EJBTHREE-1055.)
So either we don't allow it, or it's a JBoss specific feature.

[bdecoste]

The problem is only for @Service beans because we instantiate at deploy time - I still like the idea of being flexible. We support injection at instantiation but give the flexibility to inject at invocation.