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Subject: Re: [sca-j] JAVA-1: Source code for SCAClientFactory proposal - somethoughts
Mike,
I had a look at DocumentBuilderFactory and it seems to use code
that looks very similar to that written by Mark. This code is
in another non-public class FactoryFinder that is used by
DocumentBuilderFactory to delegate the lookup processing.
What is it specifically about Mark's current proposal that you
think would be improved by using a DocumentBuilderFactory-like
approach? From where I sit, they seem very similar.
Simon
Mike Edwards wrote:
>
> Mark,
>
> Thank you for doing this work.
>
> Unfortunately, it takes us down a path that I am very reluctant to follow.
> - Now, in order to provide for alternative implementations, we are
> dictating an implementation style that
> is inflexible and (based on experience) even hostile to certain
> programming environments such as OSGi.
>
> There are competing concerns here, I realize, and we are going to have
> to collectively decide which are
> the most important to deal with.
>
> On the one hand, it is desirable for the client code to have a very
> simple and unchanging API to deal with.
> This leads to the desire for a concrete class such as the
> SCAClientFactory and the return of an object
> implementing the desired client API. All well and good.
>
> On the other hand, ideally, the actual code used to load the
> implementation is created entirely by the
> provider, so that the style of loading etc is not dictated by us in the
> OASIS TC.
>
> There seems also the desire to allow multiple different vendor
> implementations of providers to be used
> simultaneously (eg for access to different domains??).
>
> The ability to have a simple mechanism to allow a mock provider for
> testing purposes...
> ( - I'm not sure how your proposal really helps on this one, perhaps you
> could explain how it would work)
>
>
> Perhaps a model that might be worth investigating is the one used by the
> XML Parsers.
> This has a DocumentBuilderFactory which is an Abstract class with no
> public constructor - instead it has
> a newInstance() method which itself looks for a "real"
> DocumentBuilderFactory implementation by
> a variety of means. This allows delegation of the actual factory
> behaviour to some implementation,
> allowing the OASIS code to shirk the responsibility for this. It's not
> ideal, but it allows us to minimise the
> code we write...
>
>
> Yours, Mike.
>
> Strategist - Emerging Technologies, SCA & SDO.
> Co Chair OASIS SCA Assembly TC.
> IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
> Phone & FAX: +44-1962-818014 Mobile: +44-7802-467431
> Email: mike_edwards@uk.ibm.com
>
>
> From: "Mark Combellack" <mcombellack@avaya.com>
> To: "OASIS Java" <sca-j@lists.oasis-open.org>
> Date: 06/02/2009 10:49
> Subject: [sca-j] JAVA-1: Source code for SCAClientFactory proposal
>
>
> ------------------------------------------------------------------------
>
>
>
> Hi,
>
>
>
> I have an action item to write some code to show SCAClient as an
> interface and SCAClientFactory as a concrete class and still allow
> vendors to plug in implementations that provide the vendor specific
> functionality.
>
>
>
> The main reasons for doing this include:
>
>
>
> * Since SCAClient is an interface, it can be mocked for testing
> purposes
> * SCAClientFactory allows vendors to plug in an implementation
> without modifying the SCAClientFactory class
> * The SCA API jar can be shipped without modification by the vendors
>
>
>
> What I will do is run you through the main points of the code and how it
> works. The code could do with more polish before it is considered complete.
>
>
>
>
>
> *SCA Client Perspective*
>
>
>
> The scenario is fairly simple – some code that is running outside of the
> SCA Domain wants to lookup and use a Service that is inside the domain.
>
>
>
> The following code shows how the HelloService could be looked up and
> invoked from unmanaged SCA Code.
>
>
>
> *final* String serviceURI = "SomeHelloServiceURI";
>
> *final* URI domainURI = *new* URI("SomeDomainURI");
>
>
>
> *final* SCAClient scaClient = SCAClientFactory./createSCAClient/();
>
> *final* HelloService helloService =
> scaClient.getService(HelloService.*class*, serviceURI, domainURI);
>
> *final* String reply = helloService.sayHello("Mark");
>
>
>
> The client first calls SCAClientFactory./createSCAClient()/ that returns
> an instance of SCAClient. This SCAClient instance can then be used to
> look up the HelloService
>
>
>
>
>
> *SCAClient Interface*
>
>
>
> The main change from Mike’s original proposal is to make SCAClient an
> interface rather than a class. The main reason for this is that it
> allows mocking of the SCAClient so that it can be unit tested.
>
>
>
> The new definition of SCAClient interface would be:
>
>
>
> *public* *interface* SCAClient {
>
>
>
> <_T_> T getService(Class<T> _interfaze_, String serviceURI, URI
> domainURI)
>
> *throws* _NoSuchServiceException_, _NoSuchDomainException_;
>
> }
>
>
>
>
>
> *SCAClientFactory class*
>
>
>
> The SCAClientFactory class is responsible for providing the indirection
> from the user’s generic SCA code and the vendor’s implementation of the
> SCA Runtime. The user’s code will ask it for a SCAClient via the
> /createSCAClient/() method.
>
>
>
> The SCAClientFactory class provides this indirection to the vendor’s
> implementation by attempting to discover the class name of the vendor’s
> implementation using:
>
>
>
> * The org.oasisopen.sca.SCAClientFactory System Property
> * The META-INF/services/org.oasisopen.sca.SCAClientFactory file.
>
>
>
> It is important to note that this class does not need to be updated by
> the Vendor to include their implementation. All the Vendor needs to do
> is set the System Property or provide the correct services file
>
>
>
>
>
> *What does the Vendor need to do?*
>
>
>
> The Vendor will need to provide a class that will be able to look up a
> Service in their SCA Runtime. To do this, they need to:
>
>
>
> * Provide an implementation of the
> org.oasisopen.sca.SCAClientFactorySPI interface
> * Provide a META-INF/services/org.oasisopen.sca.SCAClientFactory
> file that points to their implementation class
>
>
>
> The SCAClientFactorySPI interface has a single method that the vendors
> need to implement:
>
>
>
> *public* *interface* SCAClientFactorySPI {
>
>
>
> SCAClient _createSCAClient()_;
>
>
>
> }
>
>
>
>
>
> *Source Code*
>
>
>
> I have attached a ZIP file that contains the source code for the above.
> The ZIP file contains:
>
>
>
> Implementation of SCAClient and SCAClientFactory in the
> org.oasisopen.sca package
>
> Implementation of SCAClientFactorySPI in the org.oasisopen.sca.spi package
>
> * A sample implementation of the SCAClientFactorySPI in the
> com.myscaruntime.impl package
> * A unit test that looks up the HelloService using the SCAClientFactory
> * An Eclipse project file
>
>
>
> When loading the Eclipse project file, you may need to set the target
> JDK to match the JDK you have installed. To do this simply:
>
>
>
> * Select the Properties menu item on the Project menu.
> * Select the Java Build Path in the list on the left hand side
> * Select the JRE System Library on the right hand side
> * Press the Edit button
> * Make sure the workspace default JRE is selected and press Finish
> * Press OK
>
>
>
>
>
>
>
> I would appreciate your thoughts/comments on this proposal.
>
>
>
> Thanks,
>
>
>
> Mark
>
> Mark Combellack| Software Developer| Avaya | Eastern Business Park | St.
> Mellons | Cardiff | CF3 5EA | Voice: +44 (0) 29 2081 7624 |
> _mcombellack@avaya.com_ <mailto:|mcombellack@avaya.com>
>
>
>
> [attachment "JAVA-1_Code_Proposal.zip" deleted by Mike Edwards/UK/IBM]
>
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