Hi Tom,
We are aware of some of these issues, but I have to admit that I still
don't have a good handle on all the use-cases. One of the more straight
forward is the "wrapping" of the built-in handlers, for the case where
the framework does not want to re-implement all the existing JDK
supported protocols when it wants to add, or intercept, on a small set,
or even delegating for other reasons. I filed 8168076 [1] to track
this. Let me know if this something that would help your specific case,
or not.
For your 'base' handler, is it possible that you deploy it as a service
on the application class path ( using the new provider mechanism ), and
have it provide the context sensitivity, based on TCCL or some such?
The frameworks could register with it, and it could use the future API
envisioned by 8168076 to delegate to the JDK's built-in handlers when
needed.
-Chris.
[1] https://bugs.openjdk.java.net/browse/JDK-8168076
On 13/10/16 16:46, Thomas Watson wrote:
Now that jigsaw is prohibiting deep reflection on types provided by the
boot modules we are running into an issue with the ugly things we do [1]
in order to support multiple factories in Equinox (an OSGi
implementation). Each Equinox instance has its own context aware
ContentHandlerFactory and URLStreamHandlerFactory which serves up handlers
that are available for the particular instance of Equinox. In order to do
this we have to resort to some very ugly reflection. This allows us to
gain access to the 'base' factory object set in the VM so that each
instance of the framework can register itself with the 'base' factory. The
'base' factory handlers do the complicated work of figuring out which
factory to call based on the context which is calling the base handler.
We also resort to reflection on framework shutdown in order to flush our
factories out from the VM so that the base factory is not pinning our
framework in memory. I am also aware that the Apache Felix OSGi Framework
implementation uses similar deep reflection in its implementation. Are
there any plans in Java 9 that will make this scenario easier to achieve
without resorting to the use of deep reflection on the URL types from the
VM? If not, are there going to be command line options that will allow us
to open up deep reflection of specific VM types as a compatibility mode
until we can get a proper solution?
At a minimum I think we need someway to unset the statically set handlers
in the VM to avoid pinning our base factories. I can think of other
non-reflective ways to gain access to the base handler instance in order
to register each framework instance with the base handler. For example,
the base factory could implement a specific protocol which allows a
connection to register another framework.
But we are still left with a delima of how to wrap the handlers returned
by various framework factory instances from the base handlers. All the
interesting methods on java.net.URLStreamHandler are protected. Even
though the proxy base handler extends java.net.URLStreamHandler it is not
allowed to call the protected methods on another instance of
java.net.URLStreamHandler. We resorted to deep reflection on the
java.net.URLStreamHandler class methods to do that. The
java.net.URLStreamHandler class is not an interface so we cannot easily
create proxy classes using java.lang.reflect.Proxy.
Tom
[1] https://bugs.eclipse.org/bugs/show_bug.cgi?id=502209
