Apache Camel / xpath operation result detection - xpath

Question

Given a Camel route that is supposed to extract some inner parts of an XML message, create a new message from it then pass it on.
from(SUB_EXTRACT_XML)
.setExchangePattern(ExchangePattern.InOut)
.setBody().xpath("//mmsg:MyMessage/mmsg:AnyPayload/*", namespaces)
.setBody().simple("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n${in.body}")
.to(...)
For correct input messages like this (an "embedded" xml message is inside defined in schema by xs:any), it's working since the message is what I expect it to be:
<mmsg:MyMessage>
<mmsg:RandomTags/>
...
<mmsg:AnyPayload> <!-- xs:any in xsd -->
<some><xml/><here/></some>
</mmsg:AnyPayload>
</mmsg:MyMessage>
Given there is some issues with the XML message, such as the mmsg:AnyPayload tag is missing, so that the XPATH can't do its job:
<mmsg:MyMessage>
<mmsg:RandomTags/>
...
<some><xml/><here/></some>
</mmsg:MyMessage>
The XPATH will fail to extract the data and the entire XML message (including mmsg:MyMessage) is passed on, which is not intended. I rather throw some exception at this stage.
Question:
Is there a way to check if the xpath expression actually found the element refered to later in the route or if it failed to extract the given element(s)?
I know I could have done some schema validation of the message before and reject rubbish messages, but are there any way to see if a XPath expression fails?

Answer 1

A solution would be to use the choice() DSL in the route like this:
from(SUB_EXTRACT_XML)
.setExchangePattern(ExchangePattern.InOut)
.choice()
.when(xpath("//mmsg:MyMessage/mmsg:AnyPayload", namespaces))
.setHeader("Status", "OK") // just for another example how to transmit some variable between two routes
.setBody().simple("<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n${in.body}")
.endChoice()
.otherwise()
.log(LoggingLevel.ERROR, "LoggerName", "Error message; Stop the processing")
.stop()
.endChoice()
.end()
// Just to show the headers are following the route...
.to("DIRECT_GO_FORWARD");
from("DIRECT_GO_FORWARD")
.setExchangePattern(ExchangePattern.InOut)
.choice()
.when(header("Status").isEqualTo("OK"))
.bean(new SampleProcessor())
...
.end()
...
.to("...");
the second route is just there to show you can use the header set in the first route (and the body too).