Understanding managed beans/backing beans [duplicate]

This question already has answers here: Difference between managed bean and backing bean (11 answers) Closed 7 years ago.

I am learning Java EE 6 and I am trying to grasp the overall image of it. I am reading about JSF and how adding components. I am setting/reading values from the components to a bean which has the @ManagedBean annotation.

I have some trouble understanding it properly. What is Managedbeans? Is it just just objects that holds the state of the components? And they can have other methods as well? Where does the EJBs fit in? Does the managed bean开发者_开发知识库s invoked methods on the EJBs?

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What is Managedbeans? Is it just just objects that holds the state of the components?

A JSF Managed bean is like any other Java bean except that if it managed by JSF. In other words it is a bean that is created and destroyed by JSF as needed.

Hortsman Core JSF 2 book states.

The JSF implementation does the following:

1. Creates and discards beans as needed (hence the term “managed beans”)
2. Reads bean properties when displaying a web page
3. Sets bean properties when a form is posted

And they can have other methods as well?

Yes they can have as many methods as you may want.However you would (and should) ideally like to have your managed bean as lean as possible.For example it might have a search method but you should not be doing actually search inside this method but this search methods sole purpose should be to delegate the task to the business layer (which may or may not be EJB based) .
I other words no heavy lifting .

Where does the EJBs fit in?

EJB is your Business tier , they have big biceps and do all the heavy lifting. Since EJB3 JPA was introduced and that is also part of EJB. JPA however is the persistence tier. All EJBs except for JPA run in inside an EJB container. All Java EE complaint server provide these .

In a typical 3 tier architecture (these days however it is mostly more than 3 but 3 tiered is easier to explain. JSF is your Web tier , EJBs are your business tier and JPA which is also part of EJB specification but does not need EJB container is your ORM or Persistence tier. Do not worry about word container too much you will get used to it quickly and rarely you will have to worry about it. If you are using a Java EE server it's all setup for you.

Does the managed beans invoked methods on the EJBs?

Yes as explained above already . All the heavy lifting here. However it is not mandatory to use EJB with JSF. You could use any other framework e.g Spring or could even write simple pojos but thats an other area of discussion.

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From this link JSF - Managed Beans

Managed Bean :

Managed Bean is a regular Java Bean class registered with JSF. In other words, Managed Beans is a java bean managed by JSF framework.

From this link Creating and Using a Backing Bean for a Web Page

Backing Bean :

In JSF, backing beans are JavaBeans used mainly to provide UI logic and to manage data between the web tier and the business tier of the application (similar to a data transfer object). Typically you have one backing bean per JSF page. The backing bean contains the logic and properties for the UI components used on the page.

NB:

For a backing bean to be available when the application starts, you register it as a managed bean with a name and scope