Thank you Alex. Since it's roughly the same as JDK 8, then it's also not
worse. I defer to your explanation on that point.
Cheers,
Paul
On Wed, Mar 9, 2016 at 3:37 PM, Alex Buckley <alex.buck...@oracle.com
<mailto:alex.buck...@oracle.com>> wrote:
Presumably you would count the equivalent scenario on JDK 8 -- my
package A is in Alex.jar on the classpath and your package A is in
Paul.jar on the classpath -- as a security issue too, because some
of my classes may substitute for yours (or some of yours for mine,
depending on how the classpath is constructed).
On JDK 9, we do the "substitution" cleanly. Package A is not split.
That avoids one category of error (ClassCastException). What about
poor package B that finds itself accessing a different package A
than it was compiled with? Well, since package A is exported by a
named module, it's reasonable to assume that the named module "owns"
package A [*], and that the developer of package B co-bundled some
version of package A without renaming it. Dangerous in JDK 8,
dangerous in JDK 9. (We're trying to encapsulate the internals of a
module, which is different from trying to isolate modules from each
other.)
[*] Advanced scenario: the named module exporting A is actually an
automatic module which happened to co-bundle package A. By placing
this JAR on the modulepath to form an automatic module, it dominates
the JAR left on the classpath which also co-bundled package A.
Alex
On 3/9/2016 1:17 PM, Paul Benedict wrote:
But isn't what your proposing a security issue? Let's say my
package A
is in the unnamed module and your package A is in a named
module. You
basically took over my code; your classes will be substituted
for mine.
Cheers,
Paul
On Wed, Mar 9, 2016 at 2:38 PM, Alex Buckley
<alex.buck...@oracle.com <mailto:alex.buck...@oracle.com>
<mailto:alex.buck...@oracle.com
<mailto:alex.buck...@oracle.com>>> wrote:
On 3/9/2016 10:36 AM, Paul Benedict wrote:
From the doc:
"If a package is defined in both a named module and the
unnamed
module then
the package in the unnamed module is ignored. This
preserves
reliable
configuration even in the face of the chaos of the
class path,
ensuring
that every module still reads at most one module
defining a
given package.
If, in our example above, a JAR file on the class path
contains
a class
file named com/foo/bar/alpha/AlphaFactory.class then
that file
will never
be loaded, since the com.foo.bar.alpha package is
exported by the
com.foo.bar module."
I would like some clarification. Correct me if wrong,
but I
think this
entire paragraph is really meant to be about the
perspective from a
modularized JAR? If a module has package A, and the
unnamed
module has
package A, then of course the module's package A should
win.
However, if it is meant to be absolute language, then I
disagree.
The unnamed module should be coherent among itself.
If the
unnamed module
has package B and relies on classes from package A, it
should
still be able
to see its own package A. I don't think modules should
be able
to impact
how the unnamed module sees itself. That's a surprising
situation.
The unnamed module is not a root module during resolution.
If your
main class is in the unnamed module (i.e. you did java -jar
MyApp.jar rather than java -m MyApp), then the module
graph is
created by resolving various root modules (what are they?
separate
discussion) and only then is the unnamed module hooked up
to read
every module in the graph.
Hope we're OK so far.
If some named module in the graph exports package A (more
than one
module exporting A? separate discussion), then since the
unnamed
module reads that named module, the unnamed module will
access A.*
types from that named module.
It's hard to imagine the unnamed module NOT accessing A.*
types from
that named module. Primarily, we need to avoid a split
package
situation where code in the unnamed module sometimes
accesses A.*
types from the named module and sometimes from the unnamed
module.
You might say, OK, let code in the unnamed module
exclusively access
A.* in the unnamed module rather than exclusively access
A.* in the
named module. Then you have two problems:
1. There are issues for named modules in the same class
loader as
the unnamed module -- such named modules MUST get A.* from
the named
module rather than the unnamed module, and the class
loading
mechanism is incapable of switching based on accessor.
It'll be
common for named modules to exist in the same class loader
as the
unnamed module, as modular JARs on the modulepath and
non-modular
JARs on the classpath all end up in the application class
loader
(modular JARs as named modules; non-modular JARs jointly
as the
unnamed module).
2. While the module system is sure that package A exists
in the
named module, how would the module system possibly know
that package
A exists in the unnamed module? Scanning every class file
in every
non-modular JAR on the classpath at startup sounds bad.
Alex
