usage of @ManagedProperty in prerender method

Question

I am having a data table like below in my xhtml:

<p:dataTable var="employee"
      value="#{employeeBean.employeeLazyDataModel}">

Now in my backing bean, I have:

@ManagedBean
@RequestScoped
public class EmployeeBean implements Serializable {

    @ManagedProperty("#{" + EmployeeLazyDataModel.MANAGEDBEAN_NAME + "}")
    private EmployeeLazyDataModel employeeLazyDataModel;

    public void preRender(ComponentSystemEvent event) throws Exception {
        employeeLazyDataModel= // make a database call
    }

  // and getters + setters

Do you think I can call managedproperty inside preRender method? Please suggest. Thanks.

Answer 1

Surely this will work. The @ManagedProperty is injected directly after bean's construction. The preRenderView event listener requires an already-constructed bean before being invoked. So this is indeed guaranteed to work.

However, the canonical approach to initialize bean's state based on managed properties is a @PostConstruct annotated method. Thus, so:

@ManagedBean
@RequestScoped
public class EmployeeBean implements Serializable {

    @ManagedProperty("#{" + EmployeeLazyDataModel.MANAGEDBEAN_NAME + "}")
    private EmployeeLazyDataModel employeeLazyDataModel;

    @PostConstruct
    public void init() throws Exception {
        employeeLazyDataModel= // make a database call
    }

    // ...
}

(don't forget to remove the <f:event> from the view)

As to the "expensive operations" complaint in the comment, just put the bean in view scope if you don't want to run it on a per-request basis, but only once on a per-view basis.

@ManagedBean
@ViewScoped
public class EmployeeBean implements Serializable {

Note that the preRenderView event is fired before the view is rendered (thus, on every single HTTP request!), so you really need to keep the @PostConstruct here. Otherwise, you have to add a check if FacesContext#isPostback() returns false.

See also:

• When to use f:viewAction / preRenderView versus PostConstruct?
• ViewParam vs @ManagedProperty(value = "#{param.id}")
• How to choose the right bean scope?