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.

Unipod

I'm not sure if you can use these new annotations outside JSF/EL, but I'd start by looking at the JSR 299 spec: jcp.org/en/jsr/detail?id=299 – Preclude

Other people having problems with similar issues can also check bpcatalog.dev.java.net/ajax/jsf-ajax (related to AJAX and request mapping/handling, not getting beans by name) – Unipod

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)?

Submediant

You're second suggestion about just injecting the bean was so amazingly simple I had totally overlooked it. As always, your response is perfectly to the point. Thanks so much for your work here on SO. – Somewise

In the meantime (speaking as of JSF 2.2) it seems like the method evaluateExpressionGet was extended with a third parameter that allows to specify the expected class so casting won't be necessary anymore. PostBean bean = context.getApplication().evaluateExpressionGet(context, "#{beanName}", PostBean.class); – Deadandalive

@Marc: Has been in from the beginning. Was just a leftover from a copypaste mistake I guess. Answer has been corrected. Thank you for notifying. – Submediant

FacesContext is available even though the static utility method findBean() is defined inside a plain Java class. How is it available there in a plain Java class which is not managed by JSF? – Ben

@Tiny: it's in turn called by a JSF artifact within the same thread. – Submediant

Hi I get FacesContext context = FacesContext.getCurrentInstance(); context=null why?? and Trying to use HttpServletRequest request like this Bean bean = (Bean) request.getSession().getAttribute("ingresoSistema"); I got this: Servlet.service() for servlet servletsimple threw exception java.lang.IllegalStateException: Cannot create a session after the response has been committed. My bean: @ManagedBean(name = "ingresoSistema") @SessionScoped – Millner

@Submediant I was expecting findBean(String beanName) to be available in showcase.omnifaces.org/utils/Beans, but it's not. Is there any reason for that (other than keeping it strictly CDI)? – Sialoid

@Jasper: You can use Faces#evaluateExpressionGet() for this. – Submediant

@Submediant OK, but you would still have to use "#{" + beanName + "}", right? Or am I being lazy here? ;-) – Sialoid

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.

Praise

This is already covered by the currently accepted answer and even in a more convenient way (Class argument is namely unnecessary in this construct). – Submediant

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);

Disguise

This probably won't work in a regular servlet. The FacesContext is a per-request thread-local artefact set up by the JSF lifecycle (usually the FacesServlet). – Preclude

ValueBinding is deprecated since JSF 1.2 over 4 years ago. – Submediant

@BalusC: It shows how up to date I am lol. On a sidenote, using a search engine to research techniques is turning out to be counterproductive with all the old information out there. @McDowell: That actually makes sense. I'll do a test just to see what happens. – Disguise

Answer 4

You can get the managed bean by passing the name:

public static Object getBean(String beanName){
    Object bean = null;
    FacesContext fc = FacesContext.getCurrentInstance();
    if(fc!=null){
         ELContext elContext = fc.getELContext();
         bean = elContext.getELResolver().getValue(elContext, null, beanName);
    }

    return bean;
}

Pilcher

I try to to this from a servlet but it doesn`t work. – Millner

What if I am inside a Quartz Job and I don´t have FacesContext available? How can I get a Managed Bean from the application context? – Mablemabry

Answer 5

I had same requirement.

I have used the below way to get it.

I had session scoped bean.

@ManagedBean(name="mb")
@SessionScopedpublic 
class ManagedBean {
     --------
}

I have used the below code in my servlet doPost() method.

ManagedBean mb = (ManagedBean) request.getSession().getAttribute("mb");

it solved my problem.

Ghoul

What kind of servlet do you use? mate – Millner

It is HttpServlet. – Ghoul

Answer 6

I use this:

public static <T> T getBean(Class<T> clazz) {
    try {
        String beanName = getBeanName(clazz);
        FacesContext facesContext = FacesContext.getCurrentInstance();
        return facesContext.getApplication().evaluateExpressionGet(facesContext, "#{" + beanName + "}", clazz);
    //return facesContext.getApplication().getELResolver().getValue(facesContext.getELContext(), null, nomeBean);
    } catch (Exception ex) {
        return null;
    }
}

public static <T> String getBeanName(Class<T> clazz) {
    ManagedBean managedBean = clazz.getAnnotation(ManagedBean.class);
    String beanName = managedBean.name();

    if (StringHelper.isNullOrEmpty(beanName)) {
        beanName = clazz.getSimpleName();
        beanName = Character.toLowerCase(beanName.charAt(0)) + beanName.substring(1);
    }

    return beanName;
}

And then call:

MyManageBean bean = getBean(MyManageBean.class);

This way you can refactor your code and track usages without problems.

Cataldo