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.
Related
In JSF, I wonder how a ManagedBean understands that it should be available to an xhtml or facelet ?
To bind component values and objects to managed bean properties or to reference managed bean methods from component tags, page authors should use the Expression Language syntax.
When user make request to the page that contains EL, that refers to specific manage bean, this bean will be instantiated by JSF framework (except managed beans that have attribute eager="true", that means that managed bean is created before it is requested for the first time).
So the fact is that managed bean will be instantiated by JSF container and works as a model for the appropriate UI Component so the Facelet will know about the Bean, not vice versa
I have a requestscoped bean which can receive its data from three different viewscoped beans (from 3 different pages). The beans are JSF Managed Beans.
When I use ManagedProperty in the request scoped for 3 different view scoped beans, it instantiates the view scoped beans which is what I do NOT want. I want to simply know from which bean it is being called from and then call a specific method (different) for each bean.
How can I check which bean is instantiated and in scope so I can call the correct bean's method?
Looks like it's pretty simple. I was reading one of Balus's posts. I simply used ManagedProperty(value="#{viewScope.managedBeanName}") . It did not instantiate. For the inscope, it gave me the created bean :). Happy
Normally the default scope is the Request scope. I ve tried to delete the scope annotation and expected the bean to have a request bean scopped behaviour (by returning a submitted value on a previous page, I remember i've tried this the past and it worked fine) but i got nothing on the expression language wired to it.
So what is the default scope and why it's not the same behaviour?!
Depends on who's managing the bean.
If it's JSF via #ManagedBean, then it defaults to #RequestScoped, as mentioned in the javadoc:
If the scope annotations are omitted, the bean must be handled as if the RequestScoped annotation is present
If it's CDI via #Named, then it defaults to #Dependent, as mentioned in Weld documentation:
Finally, CDI features the so-called dependent pseudo-scope. This is the default scope for a bean which does not explicitly declare a scope type.
The effect is that the bean instance is newly created on every single EL expression. So, imagine a login form with two input fields referring a bean property and a command button referring a bean action, thus with in total three EL expressions, then effectively three instances will be created. One with the username set, one with the password set and one on which the action is invoked. In effects, this behaves the same as JSF #NoneScoped. This confirms the symptoms you're seeing.
If it's Spring via #Component, then it defaults to #Scope("singleton"), as mentioned in javadoc:
Default: "singleton"
In effects, this behaves the same as JSF #ApplicationScoped and CDI #ApplicationScoped.
Netbeans has got nothing to do with it. It's just an editing tool like notepad but then with 1000+ extra features.
See also:
what is none scope bean and when to use it?
How to choose the right bean scope?
I have a bean that does some logic, I call it logicBean,
and it has a sessionscoped bean as field with #Inject.
I use this logicbean in two situations in one JAVA EE6 Application,
1. in servlet.
2. in message driven bean.
In the second situcation, I got a excetion
"WebBeans context with scope type annotation #SessionScoped does not exist within current thread".
I know there is no sessionScope in MDB, so I made another bean, and want to
inject it to logicBean dynamicly to alternative the sessionScoped bean.
I do not know how to do this.
please help me, thanks.
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;