A new JPMS-friendly Java program packaging format

[Glavo]

Hey everyone,

Recently, I have been busy developing a new JPMS-friendly Java program
packaging format: JApp (https://github.com/Glavo/japp).

JApp is intended as a better alternative to shadow jar (fat jar).
Users need to specify the module path and classpath when creating a JApp
file.
Resources in all module path/classpath entries (JAR or directory) are
packaged into a single japp file,
but unlike shadow jars, japp isolates resources from different module
path/classpath entries.

For example, we can create a japp file with the following command:

    japp create -o myapp.japp \
--module-path commons-lang3-3.14.0.jar:commons-io-2.15.1.jar \
        --classpath guava-32.1.3-jre.jar:gson-2.10.1.jar


This will create a japp file named `myjapp.japp` that contains resources
from four jar files.
At runtime, the URIs for the resources from the four JAR files each look
like this:

japp:/modules/org.apache.commons.lang3/org/apache/commons/lang3/ObjectUtils.class
japp:/modules/org.apache.commons.io/org/apache/commons/io/IOUtils.class
japp:/classpath/guava-32.1.3-jre.jar/com/google/common/collect/Multimap.class
japp:/classpath/gson-2.10.1.jar/com/google/gson/Gson.class
At runtime, each entry in the module path and classpath is independent,
just like passing the `--classpath`/`--module-path` option directly to the
`java` command.

By sharing the class constant pool, using zstd as the compression method,
and
compressing the file metadata, japp files are generally smaller than shadow
jars.

JApp files also support specifying some conditions, such as requirements
for the Java version.
JApp selects the Java runtime to use to run the program based on these
conditions.

Here is its GitHub repository, for more features and detailed instructions
please refer to the README:

    https://github.com/Glavo/japp

Now that the basic features of JApp are complete, I'm sharing it here in
the hope
that more people will try it and give feedback.

Thank you to everyone who is willing to read this email!

Glavo
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