I have the following UserView class:
#ManagedBean(name="usersView", eager=true)
#ApplicationScoped
public class UserView
{
...
public void setUsers(...)
{
...
}
}
I then have another class, UserService which tries to access this bean and then call this method, as follows:
UserView usersView = (UserView) FacesContext.getCurrentInstance().getExternalContext().getSessionMap("usersView");
usersView.setUsers(...)
My issue is, is that usersView keeps coming back as null and hence the method cannot be called.
My end goal is to use this data in a PrimeFaces datatable, like so:
<p:dataTable var="user" value="#{usersView.users}" ...>
I have also tried changing the scope to SessionScoped, but it is still null and I cannot figure out why.
Any suggestions would be greatly appreciated.
The getExternalContext().getXxxMap().get("beanName") approach won't autocreate beans if they don't exist yet. Managed beans will only be autocreated when an EL expression referencing the bean is evaluated. Accessing the scope map doesn't do that. For that, use #ManagedProperty in the source bean instead. You can specify an EL expression in its value.
#ManagedProperty("#{userView}")
private UserView userView; // +setter (no getter required).
Note that this only works if the source bean has the same or a narrower scope than the target bean. If that's not the case, consider managing beans using CDI instead of JSF. You can then use #Inject instead of #ManagedProperty (which doesn't require a setter by the way). Moreover, #ManagedBean and friends is deprecated in upcoming JSF 2.3.
As to eager=true, this has only effect on #ApplicationScoped beans. See also the javadoc (emphasis mine).
...
If the value of the eager() attribute is true, and the managed-bean-scope value is "application", the runtime must instantiate this class when the application starts. This instantiation and storing of the instance must happen before any requests are serviced. If eager is unspecified or false, or the managed-bean-scope is something other than "application", the default "lazy" instantiation and scoped storage of the managed bean happens.
...
See also:
How to choose the right bean scope?
Difference between #ManagedProperty and FacesContext.getCurrentInstance().getExternalContext().getSessionMap().get("bean")
Get JSF managed bean by name in any Servlet related class
Backing beans (#ManagedBean) or CDI Beans (#Named)?
Related
I'm new to JSF and was wondering:
If I have a controller that handles all the work for a given page and a bean that holds all the data for said page, is It necessary to have both the
#ManagedProperty(value="#{myBean}")
annotation on the controller and the
#ManagedBean(name="myBean")
#SessionScoped
annotations on the form bean?
Managed beans in JSF are used to store the state of a web page. The JSF implementation is responsible for creating and discarding the bean objects( hence the name managed bean).
For every class you write #ManagedBean, the bean object is created by the JSF implementation as and when it detects an usage of the bean with the name(you can either sepcify a bean name or leave it to JSF to use the default name-class name with the first character changed to lowercase). The object created is placed in a map of the specified scope. Each scope has a map that it uses to store bean objects which have that scope specified.
Now if you need the values of these beans in your controller, you have to inject it using the ManagedProperty annotation. Note that you would need to provide the controller with a setter method for the managedProperty.
So to answer your question, the managedBean annotation is required to tell the JSF implementation to manage the bean instance and store the values in the table specific to the session scope. And the ManagedProperty annotation is needed to use that bean stored in the current session so that you can access all of its values.
We use #ManagedBean annotation to register a java bean with a JSF framework. This is a replacement for a faces-config.xml <managed-bean> element. We typically do not use name attribute because it already defaults to a simple class name camel cased.
We use #RequestScope and other scope annotations to explicitly specify the scope we want via annotation. This is equivalent to specifying<managed-bean-scope> xml entry. If you don't specify the scope it will be defaulted to #NoneScoped.
We use #ManagedProperty and specify an EL-expression in its value attribute to use JSF-provided dependency injection engine for JSF artifacts like other managed beans with broader scopes and EL-defined variables like param. We do it in case we need the injected values in other JSF artifacts, most typically beans. The injected values are available in bean's #PostConstruct-annotated method. This is an alternative to <managed-property> xml entry.
To sum it up. Use #ManagedBean #RequestScoped to register a bean with JSF framework. Use #ManagedProperty inside this bean to be able to reference among others other JSF beans with the same or broader scopes in this bean. In case you don't need to reference other beans in the created bean you don't need to use the #ManagedProperty annotation as it's purely optional.
I have two questions:
Is it legal to access the RequestContext from PrimeFaces inside an #ApplicationScoped bean?
Must the access to the RequestContext be synchronized?
Backing bean
#ApplicationScoped
public class MyDatabaseConnection
{
public void do()
{
RequestContext ctx = RequestContext.getCurrentInstance();
// ...
}
}
index.xhtml
<p:commandButton actionListener="#{myDatabaseConnection.do}"/>
Is it legal to access the RequestContext from PrimeFaces inside an #ApplicationScoped bean?
Yes, as long as you don't assign it as an instance variable (property) of the application scoped bean.
Note that the same holds true for FacesContext, ExternalContext, HttpServletRequest, HttpServletResponse, HttpSesison, etc..etc.. They are all not application scoped and can thus cause major trouble when being assigned/shared as a property of an application scoped bean.
I must admit that your chosen bean class name MyDatabaseConnection really scares me in combination with #ApplicationScoped annotation. A database connection absolutely isn't intented to be application scoped. See also among others: Is it safe to use a static java.sql.Connection instance in a multithreaded system?
Must the access to the RequestContext be synchronized?
No, you don't need to. It's in the current code example been obtained in the method local scope and not assigned as a property of the bean.
The following answers should be helpful in understanding the meaning of "request", "session" and "application" scopes:
How do servlets work? Instantiation, sessions, shared variables and multithreading
How to choose the right bean scope?
I need to use some data saved in a view scoped bean in an other view scoped bean.
#ManagedBean
#ViewScoped
public class Attivita implements Serializable {
//
}
and
#ManagedBean
#ViewScoped
public class Nota implements Serializable {
#ManagedProperty("#{attivita}")
private Attivita attivita;
// Getter and setter.
}
Now, maybe my theory about it is still quite poor, I have noticed that when #{attivita} is injected, the Attivita constructor is invoked and thus creating another instance. Is it the right behaviour? What about if I want to reference the same instance and not create a new one?
This will happen if you're navigating from one to the other view on a postback. A view scoped bean is not tied to a request, but to a view. So when you navigate to a new view, it will get a brand new instance of the view scoped bean. It won't reuse the same bean instance which is associated with a previous view.
I understand that the attivita bean is created on the initial view and reused on postback. I understand that nota bean is associated with the new view where you're navigating to. When injecting attivita in it, it will simply get a new and distinct instance even though there's another instance in the very same request. This is all expected (and admittedly a bit unintuitive) behaviour.
There is no standard JSF solution for this. CDI solves this with #ConversationScoped (the bean lives as long as you explicitly tell it to live) and the CDI extension MyFaces CODI goes a bit further with #ViewAccessScoped (the bean lives as long as the navigated view references it).
You could however workaround this by storing the bean as an attribute in the request scope.
#ManagedBean
#ViewScoped
public class Attivita implements Serializable {
public String submit() {
FacesContext.getCurrentInstance().getExternalContext()
.getRequestMap().put("attivita", this);
return "nota";
}
}
and
#ManagedBean
#ViewScoped
public class Nota implements Serializable {
private Attivita attivita;
#PostConstruct
public void init() {
attivita = (Attivita) FacesContext.getCurrentInstance().getExternalContext()
.getRequestMap().get("attivita");
}
}
Note that this is rather hacky. There may be better solutions depending on the concrete functional requirement. Also note that you should in the nota view reference the desired Attivita bean instance as #{nota.attivita} and not as #{attivita}, because it would give you a new and different instance, for the reasons already explained before.
Your attivita bean is #ViewScoped and that doesn't guarantee that your instance will be hold in session. You need a #SessionScoped bean. However, if you need attivita for some reason to be #ViewScoped, then you can pass params through them in other ways, e.g. using viewParam or using other #SessionScoped bean between them.
Page Params
http://mkblog.exadel.com/2010/07/learning-jsf2-page-params-and-page-actions/
JSF 2 Managed Bean Scopes
http://balusc.blogspot.com.es/2011/09/communication-in-jsf-20.html#ManagedBeanScopes
This question already has answers here:
Get JSF managed bean by name in any Servlet related class
(6 answers)
Closed 2 years ago.
We are using the following code to get the managed bean instance from the context.
FacesUtils.getManagedBean("beanName");
Is it the correct way of doing it?. If multiple users access the same bean what will happen?
How the bean instances are managed?
Since FacesUtils is not part of standard JSF implementation, it's unclear what it is actually doing under the covers.
Regardless, when you're already inside a managed bean, then the preferred way is to inject the other bean as managed property. I'll assume that you're already on JSF 2.0, so here's a JSF 2.0 targeted example.
#ManagedBean
#SessionScoped
public void OtherBean {}
#ManagedBean
#RequestScoped
public void YourBean {
#ManagedProperty("#{otherBean}")
private void OtherBean;
#PostConstruct
public void init() {
otherBean.doSomething(); // OtherBean is now available in any method.
}
public void setOtherBean(OtherBean otherBean) {
this.otherBean = otherBean;
}
// Getter is not necessary.
}
But when you're still on JSF 1.x, then you need to do it by <managed-property> entry in faces-config.xml as explained in this question: Passing data between managed beans.
If you happen to use CDI #Named instead of JSF #ManagedBean, use #Inject instead of #ManagedProperty. For this, a setter method is not required.
See also:
Communication in JSF2
Get JSF managed bean by name in any Servlet related class
Backing beans (#ManagedBean) or CDI Beans (#Named)?
As to your concern
If multiple users access the same bean what will happen? How the bean instances are managed?
They are managed by JSF. If a bean is found, then JSF will just return exactly this bean. If no bean is found, then JSF will just auto-create one and put in the associated scope. JSF won't unnecessarily create multiple beans.
It is possible to access or to get a backing bean property value from another backing bean in JSF?
Yes, it is possible.
You can access another beans in the context by Application#evaluateExpressionGet(). You can also inject a bean as managed property of other bean in faces-config.xml. If you're already on JSF2, you can even use #ManagedProperty annotation like follows:
#ManagedProperty(value="#{bean}")
private Bean bean;