How to do it...

1. We are going to build a JAX-RS based application, so we will start by preparing the application to perform:

@ApplicationPath("webresources")
public class Application extends javax.ws.rs.core.Application {
}

2. Then, we create a User application as our main object:

public class User implements Serializable {

    private String name;
    private String email;

    //DO NOT FORGET TO ADD THE GETTERS AND SETTERS
}

Our User class doesn't have a default constructor, so CDI doesn't know how to construct the class when it tries to inject it. So, we create a factory class and use the @Produces annotation over its methods:

public class UserFactory implements Serializable{

    @Produces
    public User getUser() {
        return new User("Elder Moraes", "elder@eldermoraes.com");
    }

}

3. Let's create an enumeration to list our profile types:

public enum ProfileType {
    ADMIN, OPERATOR;
}

4. Here, we create a custom annotation:

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
public @interface Profile {
    ProfileType value();
}

5. Add them to an interface to prototype the user profile behavior:

public interface UserProfile {
    ProfileType type();
}

Now that we have defined the profile list and its behavior with respect to the user, we can give it a proper implementation for an admin profile:

@Profile(ProfileType.ADMIN)
public class ImplAdmin implements UserProfile{

    @Override
    public ProfileType type() {
        System.out.println("User is admin");
        return ProfileType.ADMIN;
    }   
}

And the same can be done for an operator profile:

@Profile(ProfileType.OPERATOR)
@Default
public class ImplOperator implements UserProfile{

    @Override
    public ProfileType type() {
        System.out.println("User is operator");
        return ProfileType.OPERATOR;
    }   
}

6. Then, we create a REST endpoint by injecting all the objects that we are going to use into it:

@Path("userservice/")
@RequestScoped
public class UserService {
    
    @Inject
    private User user;
    
    @Inject
    @Profile(ProfileType.ADMIN)
    private UserProfile userProfileAdmin;
    
    @Inject
    @Profile(ProfileType.OPERATOR)
    private UserProfile userProfileOperator;
    
    @Inject
    private UserProfile userProfileDefault;
    
    @Inject
    private Event<User> userEvent;

    ...

7. This method gets the user injected by CDI and sends it to the result page:

    @GET
    @Path("getUser")
    public Response getUser(@Context HttpServletRequest request, 
            @Context HttpServletResponse response) 
            throws ServletException, IOException{
        
        request.setAttribute("result", user);
        request.getRequestDispatcher("/result.jsp")
        .forward(request, response);
        return Response.ok().build();
    }

8. This one does the same with an admin profile:

    @GET
    @Path("getProfileAdmin")
    public Response getProfileAdmin(@Context HttpServletRequest request, 
            @Context HttpServletResponse response) 
            throws ServletException, IOException{
        
            request.setAttribute("result", 
            fireUserEvents(userProfileAdmin.type()));
             request.getRequestDispatcher("/result.jsp")
             .forward(request, response);
        return Response.ok().build();
    }

9. And this one does the same with an operator profile:

    @GET
    @Path("getProfileOperator")
    public Response getProfileOperator(@Context HttpServletRequest request, 
            @Context HttpServletResponse response) 
            throws ServletException, IOException{
        
            request.setAttribute("result", 
            fireUserEvents(userProfileOperator.type())); 
            request.getRequestDispatcher("/result.jsp")
            .forward(request, response);
        return Response.ok().build();
    }

10. Finally, we send the default profile to the result page:

    @GET
    @Path("getProfileDefault")
    public Response getProfileDefault(@Context HttpServletRequest request, 
            @Context HttpServletResponse response) 
            throws ServletException, IOException{
        
            request.setAttribute("result", 
            fireUserEvents(userProfileDefault.type())); 
            request.getRequestDispatcher("/result.jsp")
            .forward(request, response);
            return Response.ok().build();
    }

11. We use the fireUserEvents method to fire an event and async events over a previously injected User object:

    private ProfileType fireUserEvents(ProfileType type){
        userEvent.fire(user);
        userEvent.fireAsync(user);
        return type;
    }
    
    public void sendUserNotification(@Observes User user){
        System.out.println("sendUserNotification: " + user);
    }
    
    public void sendUserNotificationAsync(@ObservesAsync User user){
        System.out.println("sendUserNotificationAsync: " + user);
    }

12. So, we build a page to call each endpoint method:

<body>
 <a href="http://localhost:8080/ch02-
 cdi/webresources/userservice/getUser">getUser</a>
 <br>
 <a href="http://localhost:8080/ch02-
 cdi/webresources/userservice/getProfileAdmin">getProfileAdmin</a>
 <br>
 <a href="http://localhost:8080/ch02-
 cdi/webresources/userservice/getProfileOperator">getProfileOperator</a>
 <br>
 <a href="http://localhost:8080/ch02-
 cdi/webresources/userservice/getProfileDefault">getProfileDefault</a>
</body>

13. And finally, we use an expression language to print the result at the result page:

<body>
    <h1>${result}</h1>
    <a href="javascript:window.history.back();">Back</a>
</body>