Alan.Bateman at oracle.com
Fri Sep 16 15:30:35 UTC 2016
On 16/09/2016 07:21, David M. Lloyd wrote:
> Hi Alan,
> In JDK-8161269 you said  that the "null" class loader has never
> been specified to contain all Java SE types, using this as a
> justification to reject this issue as "Not an Issue", regardless of
> the compatibility impact (particularly the common case of a class
> loader with a null parent).
The context here is de-privileging non-core components so that they are
no longer defined to the boot loader with all permissions. Modules such
as java.corba, java.xml.ws, java.sql and many more have no business or
need to be defined to the boot loader. It would be nice, if over the
very long term, that we could get to the point where the only module
defined to the boot loader is java.base. I don't know if we will ever
We of course acknowledge that there is potential compatibility impact
with this change and this is why it is called out in the Risks and
Assumption section of JEP 261  as
"Some Java SE types have been de-privileged and are now loaded by the
platform class loader rather than the bootstrap class loader, as noted
above. Existing custom class loaders that delegate directly to the
bootstrap class loader might not work correctly; they should be updated
to delegate to the platform class loader, which is easily available via
the new ClassLoader::getPlatformClassLoader method."
So far then there hasn't been a lot of feedback on this. The default
loader for delegation is the system class loader so someone creating a
class loader that delegates to the boot loader is probably an advanced case.
As noted in the bug report, the ClassLoader javadoc has been updated for
Java SE 9 to define the built-in class loaders. The most important part
of this is specifying that all platform classes are visible via the
platform class loader. That works for Java SE 8 and older if you replace
"platform" with "extension". I mention this in case there is concerns
about using a new API in code that needs to be compiled for JDK 8 and
run on 8 or 9.
I don't have cycles just now to get into the topic of radically changing
the class loader hierarchy or how modules on the module path are mapped
to loaders - that topic is an order of magnitude larger than the above,
esp. once you get into all the scenarios around migration.
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