Apache Camel and SOAP

To learn more about Apache Camel I have implemented a non-trivial integration scenario using freely available SOAP web services to create a service that can return the weather at an airport.

The webservices are:

• The Airport Information Webservice to find the location of an airport
• The National Digital Forecast Database Webservice provided by http://www.weather.gov/ to find the weather at a location

My goals have been:

• Use web services from different providers
• Be able to test the routes
• Include error handling
• Try various methods for transformation

So far I’m quite happy with the results and impressed with the flexibility of Apache Camel. Have a look at the code available at AirportWeather project @ GitHub and let me know what you think.

Routes

The complete route looks like this:

The flow is synchronous and each step is implemented in a separate route to be testable, for example I can stub out entire steps of the route.

A step can be further broken down into even smaller routes, for example separating the call to the web service and the error handling:

Calling a SOAP web service

To call the web service I use Spring WS. The reason I didn’t use CXF is that the NDFD is using RPC encoding which is an old web standard not supported by the current version of CXF. The XML payload is generated using a Velocity template. This works well in this case, but later I want to compare this to JAXB generated objects from an XML schema.

Transformation

Camel has very flexible support for transformation and un/marshalling. I have tried a couple of different variations. Registering a object and simply calling a method:

Let Camel figure out which method to call:

XML unmarshalling using XStream:

XPath transformation:

Let Camel figure out how to perform the conversion:

Stubbing routes

When testing I used AdviceWith to stub out a route in the test case. I’m not really sure if this is the best way, but it works.

To make the stub actually override the endpoint it is important to call skipSendToOriginalEndpoint. I use Velocity to generate a static reply. See the AirportWeatherTest for more details.

Handling bad results

To verify the result of the invoked web service I have used a choice and rollback to signal the error, for example when the airport does not exist:

Future Camel rides

Things I will investigate further:

• Other ways to stub out routes
• Making use of camel-test
• Use CXF and JAXB to avoid creating XML payloads using Velocity (perhaps for some other web service)