Let's illustrate these ideas with a full example. We're going to implement user login/logout for an application that uses JSF. First, we'll define a request-scoped bean to hold the username and password entered during login, with constraints defined using annotations from the Bean Validation specification: This bean is bound to the login prompt in the following JSF form: Username: Password: ]]> Users are represented by a JPA entity: (Note that we're also going to need a persistence.xml file to configure the JPA persistence unit containing User.) The actual work is done by a session-scoped bean that maintains information about the currently logged-in user and exposes the User entity to other beans: results = userDatabase.createQuery( "select u from User u where u.username = :username and u.password = :password") .setParameter("username", credentials.getUsername()) .setParameter("password", credentials.getPassword()) .getResultList(); if (!results.isEmpty()) { user = results.get(0); } else { // perhaps add code here to report a failed login } } public void logout() { user = null; } public boolean isLoggedIn() { return user != null; } @Produces @LoggedIn User getCurrentUser() { return user; } }]]> @LoggedIn and @UserDatabase are custom qualifier annotations: We need an adaptor bean to expose our typesafe EntityManager: Now DocumentEditor, or any other bean, can easily inject the current user: Or we can reference the current user in a JSF view: signed in as #{currentUser.username} ]]> Hopefully, this example gave you a taste of the CDI programming model. In the next chapter, we'll explore dependency injection in greater depth.