The error is a PostgreSQL one, JDBC is just the messenger here.
ERROR: operator does not exist: integer = integer[] Hint: No operator matches the given name and argument types. You might need to add explicit type casts. Position: 37
select * from se_user where user_id in (?)
Why are you expecting: "integer IN (integer[])" to work? It isn't documented anywhere that I'm aware of.
You can write that as: "integer = ANY(integer[])" though, that is documented.