On 09/19/2017 09:34 AM, Alan Bateman wrote:
On 19/09/2017 05:37, Greg Wilkins wrote:
:
Which raises an interesting point.... with the multi versioned jar
I have
used as an example, which contains:
- org/example/Foo.class
- org/example/Foo$Bar.class
- META-INF/versions/9/org/example/Foo.class
What does the classloader do when asked to load "org.example.Foo$Bar" ?
If it loads it OK, then the JarFile enumerator/iterator/stream
should also
return it. If it throws a ClassNotFoundException, then the
JarFile enumerator/iterator/stream should skip it.
A class loader that loads from a JAR file will just map
"org.example.Foo$Bar" to entry "org/example/Foo$Bar.class" and attempt
to define the class bytes to VM. It shouldn't care if the entry comes
from the base or a versioned section. It also shouldn't care if the
class name looks like it might have been compiled from an inner class.
The one case where a custom class loader does need to know more is
when it loading resources (findResource/findResources implementation
usually). For that case then the returned URL needs to locate the
right resource and so may encode a path to a resource in a versioned
section. You'll see URLClassLoader does the right thing, as does the
built-in class loaders for cases where you have modular MR JARs on the
module path. There were a few threads on core-libs-dev discussing
whether to add a getRealName method but in the end it was kicked down
the road to re-examine later.
-Alan
Just a though,
The only problem with ClassLoader API is that it doesn't have any means
to enumerate all the resources it is able to resolve. If it had such
API, the code for scanning would be much simpler.
But how would such API look like if we know that resolving works by
delegation, might work by lazily generating the resource with a
particular path on the fly, etc... Perhaps simply by ignoring the
delegation and lazy generation and just return a stream of resources
that a particular ClassLoader instance is responsible for and are backed
by real bytes in some repository which has a means of enumeration (like
filesystem, jar file, etc...)
Regards, Peter
