Welcome on board !

set def=##class(%Dictionary.CompiledClass).%OpenId("Sample.Person.JSON")
write def.SqlSchemaName
Sample_Person
write def.SqlTableName
JSON

example:

set def=##class(%Dictionary.CompiledClass).%OpenId("oex.Dir")
write def.SqlSchemaName
oex
write def.SqlTableName
Dir 

A serious problem I also struggled with.
I think inside IRIS there is not much chance to get across the MAXSTRING limit.
 

??? OEX Conrests shows:  Start on March 7th, 2022.
I hope Feb. 7th is correct,  ???

Take care PUBLIC is a SQL Reserved Verb and may cause some troubles.
https://openexchange.intersystems.com/package/migration-pg-iris-dataset?tab=reviews

Hi Werner,
The default of Namespace USER is to be mapped as Interoperability (aka ENSEMBLE) - enabled.
If you create a new namespace, deselect the Interoperability-Enabled checkbox. 

You may of course also just delete Namespace USER and create a new one.
OR remove the mapping directly from iris.cpf. 
 

Big THANKS to @Yuri Marx  (getting red cheeks) 
You confirm, that my intention to pass along the accumulated experience works.
And I'm glad I can contribute to this community which I had in mind (~ 15years back)
but couldn't realize myself. 
So I have also to thank @Evgeny Shvarov and his team that made my "dream" true and successful.
  

from bash or whatever run csession to log into your instance.  then

user>ZN "myNamespace"
nsp>do $system.SQL.Shell()
nsp>>select * from Ens_Util.Log where ConfigName='SFTPTo.HQ.SAFETRACE.DFT' AND Text LIKE '%Put Stream%' and TimeLogged LIKE '%2021-10-16%'

and off it goes

CONGRATULATIONS !! 
It's you that keep DC moving fast!  

if you have access to WRC you may ask for an evaluation license
(also for community edition)

If the table is based on an IRIS Class (ii.e. not generated by DDL)
You may try 

/// helper for input
Property InputDate As %String;
/// real used date
Property MyDate As %Date [ SqlComputeCode = { set {*} =$ZDH({InputDate},4)},
                            SqlComputed, SqlComputeOnChange = InputDate ];

in a normal SQL INSERT using TO_DATE('12/5/1948','DD/MM/YYYY') works inside VALUES()
just a guess for LOAD DATA

As you can project ANY ClassMethod as SQL PROCEDURE I see no obvious limit to your intention.
Call yoru JAVA from IRIS with any of the available interfaces   (or nodjs, or Python, or .....)
inside a ClassMethod that you present them as  SQL_PROCEDURE.