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.

Solution 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)?

Solution 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.

Solution 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);

Solution 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;
}

View more solutions

Comments

[McDowell]

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

[Konrad Garus]

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)

[McDowell]

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).

[BalusC]

ValueBinding is deprecated since JSF 1.2 over 4 years ago.

[James P.]

@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.

[jnt30]

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.

[BalusC]

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

[Marc Juchli]

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);

[BalusC]

@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.

[Tiny]

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?

[BalusC]

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

[Fernando Pie]

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

[Fernando Pie]

What kind of servlet do you use? mate

[Fernando Pie]

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

[Anil]

It is HttpServlet.

[Jasper de Vries]

@BalusC 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)?

[BalusC]

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

[Jasper de Vries]

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