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From "Liu, Jervis" <j...@iona.com>
Subject [Review] Implement JSR-311 in CXF
Date Fri, 07 Sep 2007 03:15:50 GMT
Hi, I recently spent some time on implementing JSR-311 (JAX-RS: Java API for RESTful Web Services
[1]) in CXF. The prototype code can be checked out from branch https://svn.apache.org/repos/asf/incubator/cxf/branches/jliu.
As this is still in a prototype phase, please don’t mind uncleared warnings, funny hacked
methods etc. Any comments or feedbacks will be highly appreciated.

When I first started looking into the implementation, I actually have three different design
choices:

The first approach is to implement JAX-RS in CXF similar to Jersey [2], using the JAX-WS Provider
API as a proxy to direct request from CXF runtime to JAX-RS runtime. This might be the least
intrusive approach as from the CXF runtime’s point of view, the JAX-RS runtime is really
just an application sitting on top of CXF. On the other hand, less intrusion means less control.
Taking this approach, for example, the only information CXF runtime knows about the JAX-RS
service is that it has a method exposed as invoke(T). This may gives us difficulties later
on when we bring in management capabilities or introduce a service description language like
WADL. Another problem is a potential performance penalty. Depends on the specific JAX-WS implementation,
there is always an extra time spent on transforming input stream to the T in the Provider.invoke(T).


The second and the third approach are both implementing JAX-RS in CXF core. What distinguished
them from each other is whether or not to implement JAX-RS based on existing CXF API models.
The CXF API models I referred to are frontend APIs such as serviceFactoryBean/serverFactoryBean/Endpoint/EndpointInfo,
Binding APIs, DataBinding APIs, Transport APIs and service model etc. As I mentioned early,
the major problem with these CXF APIs is they are very WSDL-centric. To get around this, we
can either refactor CXF APIs so that at least the top abstract layer is suitable for both
WSDL-based services and non-WSDL-based services. Or we can start off a new set of APIs for
non-WSDL-based services and built JAX-RS implementation on top of them.  My prototype implementation
takes the former approach, can be briefed as below:

1. Refactored CXF APIs, so that AbstractServiceFactoryBean and AbstractEndpointFactory become
the base classes that are neutral to both WSDL-based services and non-WSDL-based services.
Also refactor Service interface so that it can represent both WSDL service model and non-WSDL
service model. The service model for JAX-RS is pretty simple, it consists of resource classes
and each resource class consists of a set of resource methods. 

2. JAXRSServiceFactoryBean extended from AbstractServiceFactoryBean, is responsible for the
creation of service model, data binding etc.

3. JAXRSServerFactoryBean extended from AbstractEndpointFactory, is responsible for creating
EndpointInfo, Endpoint, BindingFactory, ServerImpl etc.

4. Start a JAX-RS service would look very similar to Simple or JAX-WS frontend:

        JAXRSServerFactoryBean sf = new JAXRSServerFactoryBean();
        sf.setResourceClasses(BookStore.class);
        sf.setBindingId(JAXRSBindingFactory.JAXRS_BINDING_ID);
        sf.setAddress("http://localhost:9080/xml/");

        sf.create();   

I have created a simple bookstore sample, which is located under \systests\src\test\java\org\apache\cxf\systest\jaxrs.
At the moment, the JAX-RS implementation does not support sub-resource locators yet, thus
this service can only serve services for the following URLs:

http://localhost:9080/xml/bookstore  return all books
http://localhost:9080/xml/bookstore/123  return book 123


[1]. JSR-311 Spec: https://jsr311.dev.java.net/
[2]. Jersey: https://jersey.dev.java.net/

Cheers,
Jervis
 



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