Serialization with JDBC with MySQL, JAVA REST and Python REST
Of course they need to be thread safe.  You should be writing your Java server as if it were single threaded, because a Java EE app server will assign a thread per incoming request.
You also need to think about database isolation and table locking.  Will you allow "dirty reads" or should your transactions be serializable?   Should you SELECT FOR UPDATE?  That's a database setting, separate from threading considerations.
I have a project in which i use JDBC with MySQL to store some user information, Java REST for the server and Python REST for the client.
My question is: by default(i haven't changed anything in the configurations), are the http requests from the client serialized on the server's side? I ask this because i'd like to know if i need to make the database insert/delete querys thread-safe or something.