JAXP default implementation and JDK-8152063

[mark.reinhold at oracle.com]

2016/3/29 0:21:05 -0700, alan.bateman at oracle.com:
> On 28/03/2016 23:46, huizhe wang wrote:
>> Thanks David.  So I understand the dynamic nature of the server 
>> configuration. There maybe two options to solve it:
>> 
>> ...
>> 
>> 2) Add a new type FinderDelegate for processes such as the "proxy" in 
>> your case to implement. If the FinderDelegate process fails to locate 
>> a provider, it would signal the jaxp process (by returning null) to 
>> fall back to the JDK-default implementation. In other words, when the 
>> system property points to a FinderDelegate, the 4-step JAXP process is 
>> reduced to two: delegate the process to the FinderDelegate, and fall 
>> back to the system default implementation.
> 
> The devil is in the detail of course. You haven't said if the 
> FinderDelegate implementation has to be visible via the system class loader.
> 
> I think the main thing is to tread carefully and it would be very easy 
> to introduce a troublesome mis-feature here.

Indeed.

This has been an interesting discussion.  Now that I understand David's
scenario better, I suspect this is just one instance of a more general
problem, and in fact one that should be solved by a module-system
requirement we previously recorded but have not yet addressed:

  http://openjdk.java.net/projects/jigsaw/spec/reqs/#selective-binding

Let's please not add yet more complexity to JAXP, if we can help it.

- Mark