Monday Apr 23, 2012

How-to invoke a method once upon application start

A requirement on the OTN forum was to execute a method only once upon application start either for the application as a whole (all user instances) or once per application user session. In addition, the method to be executed was exposed as an Operation binding on the ADF binding layer.

One way to provide a solution to this requirement is to within the combination of a phase listener on the JSPX of JSF document level and a managed bean in application or session scope (dependent on whether the method should be executed once per application start or once per application user session).

The phase listener can be configured on a JSF document, as mentioned or in the faces-config.xml file if there is no single entry to an application. For this example, we assume a single point of entry so that the phase listener can be configured on the f:view attribute.

<f:view beforePhase="#{ManagedBean.onBeforePhase}">

The event logic is configured in a bean in request scope so it could also hold component references for the page if required.

public void onBeforePhase(PhaseEvent phaseEvent) {
 //render response is called on an initial page request 
  if(phaseEvent.getPhaseId() == PhaseId.RENDER_RESPONSE){ 
    FacesContext fctx = FacesContext.getCurrentInstance(); 
    ELContext elctx = fctx.getELContext(); 
    ExpressionFactory exprFactory =
             fctx.getApplication().getExpressionFactory(); 
    //call the managed bean in application or session scope. If the 
    //bean instance already exists, then no new instance of it will be  
    //created,in which case the "initial load" method is not executed 
   
    ValueExpression ve = exprFactory.createValueExpression(
         elctx, 
         "#{your_managed_bean_in_application_or-session_scope", 
         Object.class); 
    ve.getValue(elctx); 
  }
}

The idea for this phase listener is to reference a managed bean in application scope or session scope base on your requirement. The managed bean in session or application scope invokes the method you want to invoke once per application or user session in its post construct method

//Managed Bean in application scope
import javax.annotation.PostConstruct;
... 
@PostConstruct 
public void methodInvokeOncedOnPageLoad(){  
  //access the methods you want to invoke. If they are exposed in the  
  //PageDef file, access the BindingContext --> BindingContainer --> 
  //OperationBinding. Alternatively you can call BindingContext --> 
  //findDataControl("Name as in DataBindings.cpx") --> 
  //getApplicationModule -->  findViewObject/Execute methods 
  ...
}

Note that the Java EE @PostConstruct bean is called once for each bean instantiation. In the managed bean case, the bean is instantiated once per application or session and so is the method executed once.


        
    

Monday Mar 19, 2012

URL Task Flow vs. WSRP Portlets

A URL task flow is bounded task flow that is deployed as a stand-alone Java EE application on a remote server with its URL Invoke property set to url-invoke-allowed. The URL task flow is accessed either from a direct browser GET request or, when called from another ADF application, through the task flow call activity.

For more information about how to invoke URL task flows from a task flow call activity see chapter 15.6.4 How to Call a Bounded Task Flow Using a URL of the Oracle Fusion Middleware Fusion Developer's Guide for Oracle Application Development Framework at

http://docs.oracle.com/cd/E23943_01/web.1111/b31974/taskflows_activities.htm#CHDJDJEF

Compared to WRSP portlets, URL task flows in Oracle JDeveloper 11g R1 and R2 have a functional limitation in that they cannot be embedded as a region on a page but require the calling ADF application to navigate off to another application and page. The difference between a URL task flow call using the task flow call activity and a simple redirect to a remote Java EE application is that the URL task flow has a state token attached that allows to restore the state of the calling application upon task flow return.

A use case for a URL task flow call activity is a "yellow page lookup" scenario in which different ADF applications use an URL task flow to lookup people, products or similar to return a selected value to the calling application.

Note that URL task flow calls need to be performed from a bounded or unbounded top level task flow of the calling application. If called from a region (using the parent call activity) in a page, the region state is not recovered upon task flow return.

ADF developers recently have identified URL task flows as an architecture pattern to partition their ADF applications into independently deployed Java EE applications. While this sounds like a desirable use of the URL task flow feature, it is not possible to achieve for as long as URL task flows don't render as an ADF region.

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The Oracle JDeveloper forum ranks in the Top 5 of the most active forums on the Oracle Technology Network (OTN).



The OTN Harvest blog is a summary of selected topics posted on the OTN Oracle JDeveloper forum.



It is an effort to turn knowledge exchange into an interesting read for developers who enjoy little nuggets of wisdom





Frank Nimphius

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