Get JSF managed bean by name in any Servlet related class

Question

I'm trying to write a custom servlet (for AJAX/JSON) in which I would like to reference my @ManagedBeans by name. I'm hoping to map:

http://host/app/myBean/myProperty

to:

@ManagedBean(name="myBean")
public class MyBean {
    public String getMyProperty();
}

Is it possible to load a bean by name from a regular servlet? Is there a JSF servlet or helper I could use for it?

I seem to be spoilt by Spring in which all this is too obvious.

Answer 1

In a servlet based artifact, such as @WebServlet, @WebFilter and @WebListener, you can grab a "plain vanilla" JSF @ManagedBean @RequestScoped by:

Bean bean = (Bean) request.getAttribute("beanName");

and @ManagedBean @SessionScoped by:

Bean bean = (Bean) request.getSession().getAttribute("beanName");

and @ManagedBean @ApplicationScoped by:

Bean bean = (Bean) getServletContext().getAttribute("beanName");

Note that this prerequires that the bean is already autocreated by JSF beforehand. Else these will return null. You'd then need to manually create the bean and use setAttribute("beanName", bean).

---

If you're able to use CDI @Named instead of the since JSF 2.3 deprecated @ManagedBean, then it's even more easy, particularly because you don't anymore need to manually create the beans:

@Inject
private Bean bean;

Note that this won't work when you're using @Named @ViewScoped because the bean can only be identified by JSF view state and that's only available when the FacesServlet has been invoked. So in a filter which runs before that, accessing an @Injected @ViewScoped will always throw ContextNotActiveException.

---

Only when you're inside @ManagedBean, then you can use @ManagedProperty:

@ManagedProperty("#{bean}")
private Bean bean;

Note that this doesn't work inside a @Named or @WebServlet or any other artifact. It really works inside @ManagedBean only.

---

If you're not inside a @ManagedBean, but the FacesContext is readily available (i.e. FacesContext#getCurrentInstance() doesn't return null), you can also use Application#evaluateExpressionGet():

FacesContext context = FacesContext.getCurrentInstance();
Bean bean = context.getApplication().evaluateExpressionGet(context, "#{beanName}", Bean.class);

which can be convenienced as follows:

@SuppressWarnings("unchecked")
public static <T> T findBean(String beanName) {
    FacesContext context = FacesContext.getCurrentInstance();
    return (T) context.getApplication().evaluateExpressionGet(context, "#{" + beanName + "}", Object.class);
}

and can be used as follows:

Bean bean = findBean("bean");

---

See also:

• Backing beans (@ManagedBean) or CDI Beans (@Named)?

Answer 2

I use the following method:

public static <T> T getBean(final String beanName, final Class<T> clazz) {
    ELContext elContext = FacesContext.getCurrentInstance().getELContext();
    return (T) FacesContext.getCurrentInstance().getApplication().getELResolver().getValue(elContext, null, beanName);
}

This allows me to get the returned object in a typed manner.

Answer 3

Have you tried an approach like on this link? I'm not sure if createValueBinding() is still available but code like this should be accessible from a plain old Servlet. This does require to bean to already exist.

http://www.coderanch.com/t/211706/JSF/java/access-managed-bean-JSF-from

 FacesContext context = FacesContext.getCurrentInstance();  
 Application app = context.getApplication();
 // May be deprecated
 ValueBinding binding = app.createValueBinding("#{" + expr + "}"); 
 Object value = binding.getValue(context);