DZone continues its Refcardz series with a new, free PDF cheatsheet on dependency injection and EJB3. Written by EJB expert author, Debu Panda, it covers all the key points you need to know. The 'Dependency Injection in EJB 3' Refcard is useful for those building enterprise Java applications with EJB 3 and JPA. It lists out all the metadata annotations, describes them with examples and provides descriptions for XML elements that you can use for injection.
Dependency injection allows you to simply declare component dependencies and let the EJB container deal with the complexities of instantiating, initializing, and sequencing resources and supplying service or resource references to clients as required. Development frameworks like Spring framework originally popularized dependency injection. In EJB 3, you may think of dependency injection as the inverse of JNDI. It is the responsibility of the container to inject an object based on the dependency declaration.