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

Alan Bateman Alan.Bateman at oracle.com
Wed Aug 29 10:27:35 UTC 2012

On 28/08/2012 05:57, Joe Wang wrote:
> :
>> In DocumentBuilderFactory and SAXParserFactory the javadoc reads " 
>> Otherwise the default implementation is returned if it is on the 
>> classpath or installed as a module". I think this statement needs to 
>> be re-worked, first to remove the word "module" as it is not defined 
>> here, and also because I don't think it's the classpath. If I read 
>> the code correctly then initiating loader may actually be the context 
>> class loader and assuming the usual delegation then the default 
>> should be loaded by the boot class loader. It may be possible to 
>> borrow some of the wording from the ServiceLoader javadoc to help here.
> It seems we need to go over this again since it was intended for 
> jdk8/jigsaw. Without modules, we don't really need to put other 
> implementations over the default.  How about change it to the following:
>      * Uses the service-provider loading facilities, defined by the 
> {@link java.util.ServiceLoader} class, to attempt
>      * to locate and load an implementation of the service. If there 
> are multiple providers, the first one returned
>      * by the  {@link java.util.ServiceLoader} will be instantiated 
> and returned.
>      *
>      * If a misconfigured provider is encountered and {@link 
> java.util.ServiceConfigurationError} is thrown, the error will be wrapped
>      * in a {@link javax.xml.parsers.FactoryConfigurationException}.</p>
I think it should allow for the possibility that the default factory is 
itself installed as a service provider. To that end, I think the 
original proposed working was in the right direction, it's just that it 
used terms "classpath" and "modules" too loosely and didn't define what 
the initiating loader was. Here is some suggested wording to chew on:

"Installed providers are loaded using the service-provider loading 
facility defined by the {@link ServiceLoader} class. Providers are 
loaded using the current thread's context class loader. If the context 
class loader is {@code null} then the system class loader if used. The 
first service provider to be instantiated that is not the default 
provider is returned. If the only service provider to be located is the 
default provider then it is instantiated and returned.

If a {@link ServiceConfigurationError} is encountered when locating or 
iterating over the providers then this causes {@link 
FactoryConfigurationException} to be thrown, with the {@code 
ServiceConfigurationError} as its cause."

> :
>> In src/javax/xml/datatype/FactoryFinder.java then is there any reason 
>> why this class has to use Object? I realize that some of the factory 
>> finders are called for several types but there are few (like this 
>> one) where there is only one type involved.
> No, it doesn't. FactoryFinder for datatype and transform can be 
> dedicated.  It was believed that it and SecuritySupport should be 
> copied for each package, I think we touched this before.  I left it 
> alone, or otherwise we'd need to change all other methods in the class 
> and also the transformer factory finder, for not much performance gain.
Okay, but I do think this needs clean-up at some point.

>> DocumentBuilderFactory.java it has:
>>   catch (FactoryConfigurationError e) { throw e; }
>> I assume the catch is not needed, same thing in a few other places.
> It's not. But since the javadoc for the method defined throws, I 
> thought it's good to re-throw it within the method rather than going 
> into the finder class to know that the Error will be thrown.
I see Paul's has picked up on this in his comments too.

> :
>> I think one thing that would be really useful here is to get a 
>> summary of the behavioral and API changes that this changes brings. 
>> SchemeFactory now throws FactoryConfigurationError whereas previously 
>> errors were ignored. It would be good to summarize the others.
> Yes, I think we'll do that in the MR. There isn't a general place in 
> the Javadoc for us to do that.
I understand, I'm just saying think the list would be useful for the 
review here too.  I suggest this because there are subtle differences 
between the datatype finder and the other finders, also the 
SchemaFactory is being changed to throw an error that it previously 
didn't define, etc. You'll need this for for JCP MR too but for now I 
think it is important for the reviewers here to have the summary so that 
we know what we are reviewing.


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