How to use component binding in JSF right ? (request-scoped component in session scoped bean)

Question

Mojara 2.1.21

I've updated my question based on comments. I have two situation where a component is bound to server session bean. (Additional links with information: Binding attribute causes duplicate component ID found in the view and https://stackoverflow.com/a/12512672/2692917)

Version 1:

single.xhtml:

 <h:outputText value=... binding="#{mysessionbean.out}" />

java:

 @SessionScoped @Named public class Mysessionbean {
    UIOutput out;
    //getter and setter ....
 }

Version 2:

template.xhtml:

 <h:outputText value=... binding="#{mysessionbean.out}"

view1.xhtml:

 <ui:composition template="template.xhtml" />

view2.xhtml:

 <ui:composition template="template.xhtml" />

java:

 @SessionScoped @Named public class Mysessionbean {
    UIOutput out;
    //getter and setter ....
 }

Version 1 is ok. (At least I've not encounter any errors so far). But in version 2 the duplicate id error is occured if I navigate from one page to another. Why does it happen ? Is it safe to use (request-scoped) component (in version 1) with session scoped binding ? Are there another use cases to consider ?

Edit: Functional requirement 1:

I want to use Primefaces datatable in a view. I need some info from this datatable. (Such as selected row or row index). So binding the datatable helps me to retrieve this info.

Functional requirement 2:

Components binding in composite components. They will be bound to session scoped bean. (And used mainly on one page, but what if I used it on another page ?

Requirements 3

The situation as in "Version 2". Template with primefaces menu and session scoped binding. For this I've used the EL-Binding.

Answer 1

In JSF 2.x, unless you want to manipulate components programmatically (which is at its own also rather fishy), there is no sensible real world use case to bind components to a backing bean. For sure not if they are further not been used in the backing bean itself, or if it are solely their attributes which are been flattened out.

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As to the functional requirement of getting the current row of the data table, there are much better ways listed here, How can I pass selected row to commandLink inside dataTable?, for example if your environment supports EL 2.2:

<h:dataTable value="#{bean.items}" var="item">
    <h:column>
        <h:commandLink value="Foo" action="#{bean.foo(item)}" />

---

The two last requirements are totally unclear. At least, if you're doing something like:

<x:someComponent binding="#{bean.someComponent}" />

with in bean

someComponent.setSomeAttribute(someAttribute);
someComponent.setOtherAttribute(otherAttribute);

then you should instead be doing

<x:someComponent someAttribute="#{bean.someAttribute}" otherAttribute="#{bean.otherAttribute}" />

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Or, if you intend to be able to use the component somewhere else in the view like so

<h:inputText ... required="#{not empty param[bean.save.clientId]}" />
...
<h:commandButton binding="#{bean.save}" ... />

and the instance is further nowhere been used in the bean, then just get rid of the unnecessary property altogether:

<h:inputText ... required="#{not empty param[save.clientId]}" />
...
<h:commandButton binding="#{save}" ... />

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If there is really, really no way for some unclear reason, then split all request scoped properties of the session scoped bean out into a separate request scoped bean which you in turn bind to form actions. The session scoped one can just be injected as a @ManagedProperty of the request scoped one.

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See also:

• Binding attribute causes duplicate component ID found in the view
• How does the 'binding' attribute work in JSF? When and how should it be used?