java - Differences : @SessionScoped vs @Stateful and @ApplicationScoped vs @Singleton -

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i know, principal differences between :

  1. javax.enterprise.context.sessionscoped , javax.ejb.stateful
  2. javax.enterprise.context.applicationscoped , javax.ejb.singleton

i know @sessionscoped , @stateful allows create new instance each client. know @applicationscoped , @singleton / @stateless shared between clients.

=> when should consider it's better choose ejb, or other?

@sessionscoped denotes scope while @stateful in way call stereotype. @stateful adds number services bean, among transactional behavior , passivation.

central @stateful session behavior, indeed overlaps session scope.

the difference session scope tied http session, while @stateful open-ended user managed session, lifetime managed client has reference bean proxy.

@stateful remote beans binary (rmi) counter parts of servlets. servlets listened remote http requests browser, @stateful remote beans listened remote rmi requests applets (and later swing clients).

there unfortunately many inconsistencies between two. servlet http listener, while @stateful beans automatically brought in lot of other features. servlet shared session other servlets , shared java ee component namespace other servlets in war, while @stateful ejb every separate bean has own session , component namespace.

with introduction of local beans in ejb 2 , sharp decline of swing/applet clients remote ejb communication, function of session that's maintained @stateful bean has become less clear.

i think it's fair @stateful isn't used these days. web application http session leading, means using session scope , local @stateless beans and/or cdi beans business logic.

in cases @stateful beans needed natural support extended persistence context jpa , passivation features (servlet doesn't have standardized passivation mechanism). note @stateful , @sessionscoped (or many other scopes) can combined. advantage of combining them user code no longer needs manage lifetime, container manages this.

there's similar story @applicationscoped , @singleton, although without legacy (@singleton new thing). @applicationscoped scope, while @singleton bean type (stereotype if wish), doesn't give application scoped behavior, provides transactional behavior again, automatic locking (which can tuned via @lock) , eager construction behavior (via @startup).

although @stateful , @singleton pretty handy, current way forward in java ee seems to decompose build-in stereotypes separately useable annotations , knows, perhaps 1 day actual cdi stereotypes consisting of decomposed annotations.


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