RFR 8174151: URLClassLoader no longer uses custom URLStreamHandler for jar URLs

[Chris Hegarty]

> On 13 Feb 2017, at 22:52, Paul Sandoz <paul.sandoz at oracle.com> wrote:
> 
> Hi,
> 
> Please review.
> 
>  http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8174151-url-class-path-loader/webrev/index.html

If I understand this correctly then the only optimisation ( by-pass of
openConnection ), which is causing the problem, is when the URL
is of the form “jar:file:xxxxx!/“, right? If so, you could limit the scope
of your changes to only fall back to Loader when the nested URL
has a “file” protocol. This would give you MR JAR functionality for
"jar:http://xxx”, which is fairly common.

> This is a nasty edge case when a URLStreamHandler is registered (via the system property) to process jar: URLs.
> 
> The support for multi-release JAR files changed the implementation of ClassLoader.findResource such that the to be returned jar: URLs would not be operated on, and therefore the jar: URLStreamHandler would not be queried [*]. If the returned jar: URL is operated on by the caller then the jar: URLStreamHandler would (of course) be queried.
> 
> This is arguably an implementation detail but it does change long term established behaviour in a very delicate area.
> 
> While i find it unpalatable to do so this patch restores the previous behaviour, if a custom jar: URLStreamHandler is registered. The compromise is such a custom jar: URLStreamHandler needs to explicitly support multi-release JAR files.
> 
> Paul.
> 
> [*] Note that there are already such optimisations for file: URLs.

-Chris.