8000354: (props) Properties.storeToXML/loadFromXML need to allow for alternative implementations

[Alan Bateman]

Properties defines the loadFromXML and storeToXML methods for 
loading/storing properties in XML format. These methods are problematic 
for our efforts to modularize the JDK because of the dependency on XML. 
They are also problematic for the Compact Profiles proposal [1] as it is 
unlikely that JAXP will be present in the smallest profile.

As the XML parsing needs of Properties is relatively simple we are 
thinking about including a small footprint parser that is sufficient for 
its needs. Joe Wang is looking this. In preparation for this we need to 
decouple Properties from the parser API that it uses and this is what 
the proposal here is about.

The webrev with the proposed changes is here:

http://cr.openjdk.java.net/~alanb/8000354/webrev/

Basically it introduces a JDK internal provider interface to which the 
loadFromXML and storeToXML methods delegate. The existing code that uses 
JAXP is moved into a provider implementation and will be used when 
present. When not present then the intention is that it will fallback to 
a default implementation that is the small footprint provider that Joe 
will add later. This approach ensures that we maintain compatibility (it 
remains to be seen whether we will have to deal with a few subtle issues 
when using the tiny parser). For test purposes there is a system 
property for overriding the provider, this is also why the system class 
loader is used as the initiating loader.

I should explain that when I say  "JDK internal provider interface" then 
the service type is in sun.util.spi for now. Maybe in the future it may 
be necessary to define a standard provider interface but it is not 
needed at this time (in addition it would require getting the security 
right to do that).

Thanks,

Alan.

[1] http://openjdk.java.net/jeps/161