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.


        
    

Tuesday Feb 28, 2012

Best practice invoking business services methods from JSF beans

Recently there was an increasing interest on OTN in best practices for invoking methods exposed on the ADF Business Components client interface. There exist two options to access methods exposed on ADF Business Components application modules and view objects from a managed bean through ADF.

  • Call findDataControl(String) on the BindingContext and access the application module to invoke a method exposed on the Application Module or View Object client interface.

  • Create a method binding on a PageDef level that binds to a method exposed on the Application Module or View Object client interface

Speaking of best practices, it’s the second option  to use a method binding on the PageDef file that I recommend for the following reasons

  • ADF is about abstracting the view and controller layer from the business service implementation details. A method binding instead exposes an ID (the name o the binding) to the JSF developer, which they use to access the binding from a managed bean using the OperationBinding API. Signature or name changes of a method exposed on the business service thus don't require a change in the managed bean(s) referencing it. All changes would be applied in metadata.

  • ADF provides the OperationBinding class as an abstraction for business services methods. Configuring business service method access on the PageDef file using method bindings exposes a single and consistent API to application developers.

  • Programmatic access to a method exposed on the business service require more lines of code than accessing the same method through the binding layer

  • Direct business service access violates the recommendation to always work through the ADF binding layer and not to bypass it.

To access a method binding from a managed bean, use the following code

  BindingContext bctx = BindingContext.getCurrent();
  BindingContainer bindings = bctx.getCurrentBindingsEntry();
  OperationBinding operationBinding = 
       bindings.getOperationBinding("name_of_method_binding");
  //optional
  operationBinding.getParamsMap().put("argumentName1",value1);
  operationBinding.getParamsMap().put("argumentName2",value2);
  //invoke method
  operationBinding.execute();
  if (!operationBinding.getErrors().isEmpty()) {
     //check errors
     List errors = operationBinding.getErrors();
     ...
  }
  //optional
  Object methodReturnValue = operationBinding.getResult();


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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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