WSIF Notes

1. The Web Services Invocation Framework (WSIF) is a simple Java API for invoking Web services, no matter how or where the services are provided.


2. WSIF enables developers to interact with abstract representations of Web services through their WSDL descriptions instead of working directly with the Simple Object Access Protocol (SOAP) APIs, which is the usual programming model.


3. WSIF allows stubless or completely dynamic invocation of a Web service, based upon examination of the meta-data about the service at runtime. It also allows updated implementations of a binding to be plugged into WSIF at runtime, and it allows the calling service to defer choosing a binding until runtime.


4. The separation of the API from the actual protocol also means you have flexibility - you can switch protocols, location, etc. without having to even recompile your client code.


5. So if your an externally available SOAP service becomes available as an EJB, you can switch to using RMI/IIOP by just changing the service description (the WSDL), without having to make any modification in applications that use the service.


6. You can exploit WSDL's extensibility, its capability to offer multiple bindings for the same service, deciding on a binding at runtime, etc.


7. In the WSDL specification, Web service binding descriptions are extensions to the specification. So the SOAP binding, for example, is one way to expose the abstract functionality (and there could be others). Since WSIF mirrors WSDL very closely, it also views SOAP as just one of several ways you might wish to expose your software's functionality. WSDL thus becomes a normalized description of software, and WSIF is the natural client programming model.


8. The WSIF API allows clients to invoke services focusing on the abstract service description - the portion of WSDL that covers the port types, operations and message exchanges without referring to real protocols.


9. The abstract invocations work because they are backed up by protocol-specific pieces of code called providers. A provider is what conducts the actual message exchanges according to the specifics of a particular protocol - for example, the SOAP provider that is packaged with WSIF uses a specific SOAP engine like Axis to do the real work.


10. The decoupling of the abstract invocation from the real provider that does the work results in a flexible programming model that allows dynamic invocation, late binding, clients being unaware of large scale changes to services - such as service migration, change of protocols, etc.


11. WSIF also allows new providers to be registered dynamically, so you could enhance your client's capability without ever having to recompile its code or redeploy it.


12. A provider is a piece of code that supports a WSDL extension and allows invocation of the service through that particular implementation. WSIF providers use the J2SE JAR service provider specification making them discoverable at runtime.


13. Some bindings for which provider is available : java, ejb, jms, jca