区分不同种类的JSF托管Bean

Question

I recently read this article from Neil Griffin Making Distinctions Between Different Kinds of JSF Managed-Beans and it got me thinking about the distinction between different beans in my own application. To quickly summarise the gist:

• Model Managed-Bean: This type of managed-bean participates in the "Model" concern of the MVC design pattern. When you see the word "model" -- think DATA. A JSF model-bean should be a POJO that follows the JavaBean design pattern with getters/setters encapsulating properties.

• Backing Managed-Bean: This type of managed-bean participates in the "View" concern of the MVC design pattern. The purpose of a backing-bean is to support UI logic, and has a 1::1 relationship with a JSF view, or a JSF form in a Facelet composition. Although it typically has JavaBean-style properties with associated getters/setters, these are properties of the View -- not of the underlying application data model. JSF backing-beans may also have JSF actionListener and valueChangeListener methods.

• Controller Managed-Bean: This type of managed-bean participates in the "Controller" concern of the MVC design pattern. The purpose of a controller bean is to execute some kind of business logic and return a navigation outcome to the JSF navigation-handler. JSF controller-beans typically have JSF action methods (and not actionListener methods).

• Support Managed-Bean: This type of bean "supports" one or more views in the "View" concern of the MVC design pattern. The typical use case is supplying an ArrayList to JSF h:selectOneMenu drop-down lists that appear in more than one JSF view. If the data in the dropdown lists is particular to the user, then the bean would be kept in session scope.

• Utility Managed-Bean: This type of bean provides some type of "utility" function to one or more JSF views. A good example of this might be a FileUpload bean that can be reused in multiple web applications.

This made sense to me and for the past few hours I have been refactoring my code and came up with the following with respect to the user login:

The AuthenticationController is an example of a Controller Managed-Bean. It is request-scoped and features two getters and setters for setting a username and password, and two navigation methods, authenticate and logout , navigating the user to either their private area upon successful login, or back to the main page when logging out.

The UserBean is an example of a Support Managed-Bean. It is session-scoped and features an instance of User class (which would be null when you are not authenticated) with a getter and setter, nothing more.

The AuthenticationController has this user as a managed property ( @ManagedProperty(value = "#{userController.user} private User user; ). Upon successful authentication, the AuthenticationController would set the managed property to the actual user instance with the corresponding username that was used for the login.

Any new beans would be able to grab the user as a managed property as well and pull the data they need, such as group membership for instance, if the User class would feature a list with group names.

Would this way be the proper way to go about with regard to the seperation of concerns?

Answer 1

This is a very subjective question. I personally disagree that article and find that it's giving really bad advice to starters.

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Model Managed-Bean: This type of managed-bean participates in the "Model" concern of the MVC design pattern. When you see the word "model" -- think DATA. A JSF model-bean should be a POJO that follows the JavaBean design pattern with getters/setters encapsulating properties.

I would absolutely not make or call it a managed bean. Just make it a property of a @ManagedBean . For example a DTO or JPA @Entity .

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Backing Managed-Bean: This type of managed-bean participates in the "View" concern of the MVC design pattern. The purpose of a backing-bean is to support UI logic, and has a 1::1 relationship with a JSF view, or a JSF form in a Facelet composition. Although it typically has JavaBean-style properties with associated getters/setters, these are properties of the View -- not of the underlying application data model. JSF backing-beans may also have JSF actionListener and valueChangeListener methods.

This way you keep duplicating and mapping the properties of the entity in the managed bean. This makes no sense to me. As said, just make the entity a property of the managed bean and let the input fields refer it directly like #{authenticator.user.name} instead of #{authenticator.username} .

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Controller Managed-Bean: This type of managed-bean participates in the "Controller" concern of the MVC design pattern. The purpose of a controller bean is to execute some kind of business logic and return a navigation outcome to the JSF navigation-handler. JSF controller-beans typically have JSF action methods (and not actionListener methods).

This describes the @RequestScoped / @ViewScoped @ManagedBean class pretty much. Whether event listener methods are allowed or not depends on whether they are specific to the view which is tied to the bean and/or are for their job dependent on the bean's state. If they are, then they belongs in the bean. If not, then they should be a standalone implementation of any FacesListener interface , but definitely not a managed bean.

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Support Managed-Bean: This type of bean "supports" one or more views in the "View" concern of the MVC design pattern. The typical use case is supplying an ArrayList to JSF h:selectOneMenu drop-down lists that appear in more than one JSF view. If the data in the dropdown lists is particular to the user, then the bean would be kept in session scope.

Fine. For application wide data like dropdown lists just use an @ApplicationScoped bean and for session wide data like logged-in user and its preferences just use a @SessionScoped one.

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Utility Managed-Bean: This type of bean provides some type of "utility" function to one or more JSF views. A good example of this might be a FileUpload bean that can be reused in multiple web applications.

This makes not really sense to me. Backing beans are usually tied to single views. This sounds too much like an ActionListener implementation which is to be used by <f:actionListener> in command components to your choice. Definitely not a managed bean.

For kickoff examples of the right approach, see also:

• Hello World example in Our JSF wiki page
• "Bookstore CRUD" example in this answer
• "Master-detail" example in this answer
• JSF Service Layer
• Communication in JSF 2