Handling an empty xml backend response in WSO ESB

Question

A WSO2-ESB Service is recieving an 'empty' XML response from an endpoint in some cases.

Usually the response looks like this. It contains several results:

<?xml version='1.0' encoding='UTF-8'?>
<S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
    <S:Body>
        <ns2:results xmlns:ns2="http://the-endpoint.com/">
            <result>some result</result>
            <result>some other result</result>
            <result>some very different result</result>
        </ns2:results>
    </S:Body>
</S:Envelope>

which is then translated to an array of results and consumed by clients.

{"results": ["some result", ...]}

But in some rare cases the endpoints response is just an empty list of results which is translated to an empty <ns2:results/> tag by JAX-WS appearently.

<?xml version='1.0' encoding='UTF-8'?>
<S:Envelope xmlns:S="http://schemas.xmlsoap.org/soap/envelope/">
    <S:Body>
        <ns2:results xmlns:ns2="http://the-endpoint.com/"/>
    </S:Body>
</S:Envelope>

WSO2-ESB then translates this to a null object, which is causing trouble.

{"results": null}

Now how can I make the WSO2-ESB Webservice return the empty list as {"results": []} in case there is an empty response?

Answer 1

You need to add XML processing instructions to the outer element using XSLT mediator.

You can refer to this blog on adding processing instruction. https://medium.com/@CKoutsoumpos/wso2-esb-handle-empty-or-single-item-arrays-during-json-transformation-with-xslt-c1d5a778a548