Hi,

thanks a lot for this library. I have forked it and rewritten/fixed some parts here: https://github.com/invesdwin/invesdwin-context-julia/tree/main/invesdwin-context-julia-parent/invesdwin-context-julia-runtime-juliacaller/src/main/java/de/invesdwin/context/julia/runtime/juliacaller/pool

• use begin/end to support multi line commands
  • need to escape newlines when sending through the socket
• Pkg.installed is deprecated, I have implemented a workaround using Pkg.dependencies()
• there was no way to read the stdout from the java side
• there was no way to react to errors (stderr) from the java side
  • though the current solution can not differentiate between warnings (e.g. deprecation) and errors sadly
• replaced org.json with jackson (better handling of array vs object)
• make it recover from more error cases (e.g. errors during "get" operations and don't close during errors in "exec" operations)

If you like you can have a look and backport some fixes. The fork also includes a testsuite for writing/reading various data types (including vectors and matrices).
Though I guess https://github.com/org-arl/jajub could be a more sophisticated solution since it seems to support binary transport and does not require a socket. But still, it is good to have options to choose between. Using json/socket based communication might be more robust long term, despite being slower.