A simple code below will demonstrate that warnings generated by Derby running in Server mode do not make their way to client. The client code below is trying to create the database db1drda which already exsits. Server generates a warning for that but the client cde below does not print it.
con = DriverManager.getConnection("jdbc:derby:net://localhost:1527/db1drda;create=true:retrieveMessagesFromServerOnGetMessage=true;", "app", "app");
SQLWarning warnings1 = con.getWarnings();
System.out.println("database exists, should get warning");
while (warnings1 != null)
System.out.println("warnings on connection = " + warnings1);
warnings1 = warnings1.getNextWarning();