RFR [JDK8]: 7169894: JAXP Plugability Layer: using service loader

[Alan Bateman]

On 31/08/2012 08:59, Joe Wang wrote:
>
> Yes, it works just fine under normal conditions.
>
> Note the old process: read the service file using TCCL (if null, 
> system cl), if nothing found, then BCL
>
> Somehow I was under the impression ServiceLoader does just that so 
> that we could delegate to it.  It's probably a good thing that it 
> actually doesn't. If it did, it'd cause error in the following case:
>
>    The TCCL's parent is BCL  (that is Bootstrap), a jaxp impl (e.g. 
> Xerces) is on the classpath
>     Old process: try TCCL, not found, try BCL, not found
>     ServiceLoader: use TCCL, not found, return null  (I thought it'd 
> continue using System CL, but it didn't)
>
>     **although worked differently, the results are the same, so not an 
> issue in terms of the result, still a behavior change though.
>
> I did many tests, but so far the results are the same before and after 
> the patch.
>
> If TCCL is set to null, I actually saw SCE other than SchemaFactory, 
> for example:
> javax.xml.stream.FactoryConfigurationError: 
> javax.xml.stream.XMLEventFactory: Provider 
> org.apache.xerces.stax.XMLEventFactoryImpl not found
>
> --Joe
This is a mess. I realize it pre-dates your watch but it looks like 
we're going to have to sort this out in order to make progress. I think 
sorting this out will require some behavior changes so that the 
factories are located in a consistent manner and also work consistently 
when there is a security manager set.

So what would you think about putting the ServiceLoader changes on hold 
for a little bit and spending some time to get the factory finders 
working consistently. I hope this will be mostly just fixing the 
SecuritySupport.getContextClassLoader implementations and so will not 
conflict with the SL work. As part of this then we get a list of 
existing vs. proposal behavior for each factory and for each of the 
security manager + no security manager cases. This will allow us to 
assess the impact to each factory finder. My gut feel is that the impact 
will not be too significant and in most cases will be an improvement to 
how it works today.

I also agree with Paul about getting a useful set of tests as it's 
impossible to say from reading the javadoc how it should behave. These 
tests will help you to get the list of current behavior, proposed 
behavior and should give you confidence when you get to the changing 
this code to use ServiceLoader.

-Alan