[GitHub] plamentotev opened a new pull request #2: [MJAR-238] Allow setting of module main class

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plamentotev opened a new pull request #2: [MJAR-238] Allow setting of module main class
URL: https://github.com/apache/maven-jar-plugin/pull/2
 
 
   This pull request adds support for modular JAR files. Of course it was possible to create JAR files that contains `module-info.class` but the `jar` tools part of the JDK does more that that. It allows the module main class and version to be specified, adds the list of the packages included in the module and verifies that the module descriptor is correct.
   
   This PR modifies the JAR plugin to use the new `ModularJarArchiver` so the above mentioned information can be added to the module descriptor as well to the validated.  `ModularJarArchiver` handles gracefully non-modular JAR archives so it is safe to be used for all JAR files without prior knowledge if the archive is going to contain `module-info.class` or not.
   
    `ModularJarArchiver` requires the JDK used to run Maven to be 9 or newer in order to modify the module descriptor as the current implementation (`JarToolModularJarArchiver`) uses the JDK `jar` tool and does not support tool chains. If the JDK used is 8 or older then `ModularJarArchiver` will gracefully fallback to treating the archive as regular JAR file and will just pack the module descriptor without modifying or validating it.
   
   The current implementation does not allow the user to specify the module version, but that is not a problem as it is set by the compiler plugin. And if needed could easily be added later - `ModularJarArchiver` already support specifying the module version.
   
   
    - [x] I hereby declare this contribution to be licenced under the [Apache License Version 2.0, January 2004](http://www.apache.org/licenses/LICENSE-2.0)
   

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