Techie Madness

| Class | Package | Subclass | Subclass | World | | |(same pkg)|(diff pkg)| ————————————+———————+—————————+——————————+——————————+———————— public | + | + | + | + | + ————————————+———————+—————————+——————————+——————————+———————— protected | + | + | + | + | ————————————+———————+—————————+——————————+——————————+———————— no modifier | + | + | + | | ————————————+———————+—————————+——————————+——————————+———————— private | + | | | | + : accessible blank : not accessible

 EJB is part of Java EE. Spring is a standalone framework which substitutes and improves many parts of Java EE. Spring doesn't necessarily require Java EE to run. A barebones servletcontainer like Tomcat is already sufficient. Simply put, Spring is a competitor of Java EE. E.g. "Spring" (standalone) competes EJB/JTA, Spring MVC competes JSF/JAX-RS, Spring DI/IoC/AOP competes CDI, Spring Security competes JAAS/JASPIC, etc.

For  stateless session beans  the server can maintain a variable amount of instances in a pool. Each time a client requests such a stateless bean (e.g. through a method) a random instance is chosen to serve that request. That means if the client does two subsequent requests it is possible that two different instances of the stateless bean serve the requests. In fact there is no conversational state between the two requests. Also if the client disappears, the stateless bean does not get destroyed and can serve the next request from another client. On the other hand a  stateful session bean  is closely connected to the client. Each instance is created and bounded to a single client and serves only requests from that particular client. So happens that if you do two subsequent requests on a stateful bean, your request will be served always from the same instance of the bean. That means you can maintain a conversational state between the requests. At the end of the li...