The reasons for this are:
In order to use the same transaction, the procedure must use the same connection as the parent SQL statement in which the method was executed. Connections re-used in this way are called nested connections.
Use the connection URL jdbc:default:connection to re-use the current
The Database Connection URL jdbc:default:connection allows a Java method
to get the Connection of the SQL statement that called it. This is
the standard (SQL standard, Part 13 SQL Routines and Java) mechanism to obtain
the nested connection object. The method would get a
Loading a JDBC driver in a database-side routine is not required.