EJB high level

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  • Separates transaction and security metadata from bean
  • Provides transaction management, state management, resource pooling, security
  • if not using security or transactions question if you need EJB

EJB3

  • No longer have to lookup home and do create. Bean created automatically when looked up.
  • Tend to be called "Entity" in EJB 3 and "Entity Bean" in EJB 2.0

JPA

Defines:

  • Creation of ORM (Object-Relational Mapping) metadata
  • Entity Manager API - API for CRUD - persistence operations
  • JPQL (Java persistence query language) - searching & retrieving

Designed to also exist outside application server

Entity Manager

  • Reads ORM metadata
  • Persists data - performs CRUD operations
  • Handles life-cycle - performance tuning - cache, transaction management

JPQL

Supports:

  • inner joins
  • outer joins
  • bulk updates
  • delete
  • sub queries
  • Does not support full sql

Also supports native queries - exam doesn't consider this as full sql

Terminology

EJB 3

  • Remote business interface - the @remote interface
  • Supports annotations and deployment descriptors
    • deployment descriptor overrides
      • So can deploy in different environments without changing code
  • No longer have to implement lifecycle callbacks
    • can put lifecycle callbacks in a separate class
 public class FooListener{
   @PrePassivate public void doPrePassiveStuff() {
      ....
   }
 }
 @CallbackListener FooListener
 @stateful
 public class FooBean{

EJB 2

  • Remote home interface - factory for creating bean
  • Component interface - clients view - interface of the bean
    • remote component interface - remote proxy for accessing the bean
    • local component interface (also known as local client)
  • Business interface - interface implemented by the remote component interface and the bean

EJB 2

  • Home - javax.ejb.EJBHome - factory pattern to create instance of EJB
  • Remove - javax.ejb.EJBObject - proxy for accessing the bean
  • Bean
    1. javax.ejb.Session - information to persist
      1. Stateless - Do not hold conversational state - no guarentee the client will call same bean
      2. Stateful - Can hold state - will be the same bean across client calls e.g. shopping basket
        • also use to for workflow
    2. javax.ejb.Entity - the implementation containing business logic