Question

I have a little problem I can’t solve so far. In BPEL I want to create an onAlarm eventHandler which fires immediatly (i.e. the “for” element is set to ‘PT0S’) and repeats every 2 seconds. This eventHandler shall contain a counter which increments every time the alarm fires.

The question is: How to initialize the counter? If the variable will be initialized within the onAlarm scope the value would not increment anymore. In the “normal” control flow the value also cannot be initialized, because it is not defined if the process or the onAlarm scope runs first. So I would get every now and then an uninitializedVariable exception.

My solution would be to not initialize the variable neither in the process scope nor in the onAlarm scope, but create a faultHandler wherein the variable will be initialized and afterwards the onAlarm flow will be executed. Problem is every uninitializedVariable execution will be caught now by this faultHandler and there may be another too.

So is there another possibility to deal with this problem or can I somehow find out which variable wasn’t initialized properly so the faultHandler can get two control flows?

The solution should work on every BPEL engine.

Thanks, Michael

Answer 1

You can initialize a variable with a default value on its definition using a from-spec just like in an assignment. See section 8.4.1 of the spec for the details.

A default initialization can look like this:

<variables>
    <variable name="Default" type="xsd:int" >
        <from>5</from>
    </variable>
</variables>

This should work as eventHandlers are installed after the start activity of a process has completed. By then, the variables defined in the root scope have already been initialized. To quote the spec, section 12.1:

Scope initialization consists of instantiating and initializing the
scope’s variables and partner links; … If a scope contains an
initial start activity then the start activity MUST complete before
the event handlers are installed.

So much for spec. I think nobody can tell whether this “works on every BPEL engine”. As far as I know, it works on bpel-g, Orchestra and EasyBPEL, but not on Apache ODE or OpenESB.