Adding module descriptor to existing JAR file

[Alan Bateman]

On 06/02/2017 08:41, Gunnar Morling wrote:

> Hi,
>
> I'm trying to convert an existing non-modular JAR into a modular JAR.
>
> Using jdeps, I was able to generate a module-info.java descriptor for
> the module-to-be. And the help text of the "jar" command discusses how
> to add a compiled module descriptor to an existing JAR:
>
>      jar --update --file foo.jar --main-class com.foo.Main --module-version 1.0
>       -C foo/ module-info.class
>
> I'm struggling though with compiling the module descriptor. I tried
> with --patch-module and also by providing the existing JAR via
> --class-path (as it's not a module yet), but javac is complaining
> about the exported packages from the module-info.java not being found:
>
>      module-info.java:7: error: package is empty or does not exist: com.foo
>           exports com.foo
>
> Is there an example somewhere that shows how to use javac for
> compiling a module descriptor, given the classes from a non-module
> JAR? I'm looking for a way without re-compiling that entire JAR, as I
> don't think that's practical or even possible in some cases.
>
If the classes in the module are in the output directory then javac 
should be able to compile the module-info.java. For the foo.jar example 
then I would expect this should work:

mkdir classes
(cd classes; jar xf ../foo.jar)
javac -p <modulepath> -d classes module-info.java
jar uf foo.jar -C classes module-info.class

The recipe is similar to what one would do when compiling the classes 
for an older release and then compiling the module-info.java with a 
separate javac command.

-Alan