Friday, July 01, 2016

Oracle SOA: Using Sensors on Optional Elements

In this posting I describe an issue you may run into when configuring composite sensors on optional elements, and why it is good practice to always add a filter that checks if the element is actually present.

If you define a sensor on a composite to record elements that are optional, you may find an error in the logs similar to the below:

If that is the case you probably have a composite that takes a request with one or more optional elements, of which one or more are not provided, which then is transformed by an XSLT. I have only seen it in combination with a Mediator, but don't know if it would happen in case of BPEL or BPM as well.

For some reason (a product limitation, if not a bug) it will try to store the sensor with a null value, which will result in the above error. You will not see the error when the input is being mapped using XPath, as then it will not try to store the sensor.

To make it always work, the solution is to add a filter on the value to make it only store the value if the element is actually there. I will now explain how to do that.

Let's assume you have a payload like this:

If you want a sensor on the secondElement, you can add a sensor by right-mouse clicking the service and choose Configure Sensors:

For this optional element you should configure it as follows:

It may look a bit like overkill to always do it, but then again if you do it right away, you no longer have to worry about it later, as it will always work, XSLT or not. 

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