CODEWITHSUNDEEP
jsfjakarta-eeservletsjsf-2managed-bean
Konrad Garus
Konrad Garus

Reputation: 54015

Get JSF managed bean by name in any Servlet related class

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.

Upvotes: 106

Views: 159216

Answers (6)

BalusC
BalusC

Reputation: 1108722

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:

Upvotes: 275

Anil
Anil

Reputation: 347

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.

Upvotes: 0

Soujanya
Soujanya

Reputation: 21

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;
}

Upvotes: 3

ChRoNoN
ChRoNoN

Reputation: 900

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.

Upvotes: -1

John Yeary
John Yeary

Reputation: 1113

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.

Upvotes: 11

James P.
James P.

Reputation: 19617

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);

Upvotes: 3

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