CDI is an abbreviation of “Context and dependency injection” and it is defined in the JSR 299. I this post, I don’t introduce CDI in detail. For that I refere to well sources as en.wikipedia, JCP, DZone Ref-Card and also to good article in TheServerSide.com. I will explaine that things, that the most students grappled with it.

CDI isn’t activated out-of-the box in a Java EE 6 application. It is necessary to put a beans.xml deployment description file inside your Project (“…srcconf” – folder). You need it inside a Web Application(to use it with JSF/JSP/etc) as well as in an EJB-Module(if it exists, too). The file can be “empty” as follow:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
http://java.sun.com/xml/ns/javaee/beans_1_0.xsd">
</beans>

Why should I use CDI

It is the easiest way to get handy with a Java EE 6 Application. CDI unify all of the various types of beans to “Managed Beans”. So forget “Backing Bean”, “Entity Bean”, “JSF-Managed Bean”, etc. Every POJO which is marked as a ManagedBean is managed by the Java EE Container.

What is the benefit of CDI

• You can simply inject every POJO inside your application
• The Context of the first call define the life cycle of all following bean calls (in the most case, it starts with a defined scope)
• A ManagedBean can simply extended with enterprise-services with an EJB-Annotation (as @javax.ejb.Stateless, @javax.ejb.Stateful, @javax.ejb.Singleton)

Here are more information about ManagedBean and the “extension” EJB.

Which annotation do I need to make a ManagedBean?

In short: Use @javax.annotation.Named
In detail: When you use @javax.annotation.Named on the top of your class, you get implicit the @javax.annotation.ManagedBean.

What is the different between the annotation: @javax.faces.bean.ManagedBean(name=”myBean”); @javax.annotation.ManagedBean(“myBean”) and @javax.inject.Named(“myBean”)?

In short: there is no different, use @javax.inject.Named
In detail: @javax.faces.bean.ManagedBean is refer to JSR314 and was introduced with JSF 2.0. The main goal was to avoid the configuration in the faces-config.xml file to use the bean inside an JSF Page. The annotation @javax.annotation.ManagedBean(“myBean”) and @javax.inject.Named(“myBean”) are almost the same, but the Named is shorter . See here

What is the different between the Annotation @SessionScoped and @Stateful

In short: They are similar in some ways. Both don’t lose their states after a single call and both are ManagedBeans, but you use it on different location inside your application.
In detail: The Scoped-Annotations (@RequestScoped, @SessionScoped, etc.) are used in the client /web tier. Beans with a EJB-Annotation as like @Stateful or @Stateless (or @Singelton – see type of EJB’s) are located in the business tier. So the user interacts with a scoped annotated bean, where the Scoped annotated bean it self interacts with an EJB annotated Beans (of corse they can also interact with an other normal ManagedBean).
Keep in mind, that a Stateful Bean is only Stateful inside the callers context. I made a diagram, that should explain this behavior. Look at the Object Reference of each call (Ref: …). As I described here, not every combination make sense, i.e. a RequestScoped ManagedBean inject a Stateful ManagedBean.

When should I use the Annotation @EJB or the @Inject and when should I instance (new Class()) an object by my self

In short: Use @Inject
In detail:@EJB and @Inject are almost the same. In the most case you can use both, but

• @Inject is like generic and takes only the jndi-Name. In the most case you can use that
• @EJB can inject local and remote Beans. You need it, inside a Client Application which call an EJB inside a Java EE Container (remote call)
• new Class() is used for business functions. When you instance an object by your self, it isn’t managed by the container and you can’t use container managed functions (i.e. inject an other bean or a resource as a JMS Queue