RFR 8156497: Add jar tool support for Multi-release modular JARs

[Chris Hegarty]

> On 20 May 2016, at 17:01, Jonathan Gibbons <jonathan.gibbons at oracle.com> wrote:
> 
> It would be good if (eventually) there were test cases involving the use
> of MRM jars, both via the JarFile API and jar-fs file system, perhaps
> extending to the use of MRM jars in javac as well.

I agree.

Just to note, the updated test in the webrev is already exercising the JarFile
API, indirectly. Support for Modular JARs on the module path uses the 
JarFile constructor that accepts a JarFile.Release value when opening.
The test exercises this when it verifies the newly created, or updated, JAR
file by running the module’s entry point.

But I agree, more test scenarios will need to be added.

-Chris.

> -- Jon
> 
> On 05/20/2016 08:55 AM, Chris Hegarty wrote:
>> What do you get if you mix JEP 261 [1] with JEP 238 [2]?
>> A Multi-release modular JAR.
>> 
>> This issue proposes to add support to the jar tool for creating and
>> updating modular JAR files with an optional module-info.class in the
>> versioned section.
>> 
>> MRJARs are intended to target multiple releases of the Java platform, so
>> it seems reasonable for a Multi-release modular JAR ( MRMJAR ) to be
>> able to declare a different set of dependencies on modules that are part
>> of the Java platform. The reasoning here is that these are
>> implementation details rather than parts of a module's API surface, and
>> that one may well want to change them as the JDK itself evolves. The
>> runtime already has support for loading from the versioned section.
>> 
>> Specifically, a versioned module descriptor must be identical to the
>> root module descriptor, with two exceptions:
>> 
>> - A versioned descriptor can have different non-public `requires`
>> clauses of platform ( `java.*` and `jdk.*` ) modules, and
>> 
>> - A versioned descriptor can have different `uses` clauses, even of
>> service types defined outside of `java.*` and `jdk.*` modules.
>> 
>> http://cr.openjdk.java.net/~chegar/8156497.00/
>> 
>> Note: while there are some new test scenarios added, which give
>> reasonable coverage, further tests will be added later. Steve has some
>> additional jar tools support coming for easier creation of MRJARS.
>> 
>> -Chris.
>> 
>> [1] http://openjdk.java.net/jeps/261
>> [2] http://openjdk.java.net/jeps/238
>