What would happen if this runs?

Question

This is a 'real' code example that i found in this program. Could this cause connection pools to not be relased
Connection con = null;
stmt = con.createStatement();
int ret = stmt.executeUpdate(simple query);
con.commit();
con.rollback();
con.commit();
con.close

Answer 1

Connection con = null;
stmt = con.createStatement();You will get a NullPointerException here. :P
If we assume that you are getting a Connection from a DataSource...
int ret = stmt.executeUpdate(simple query);
con.commit();This should commit the updates (even if the auto-commit mode is set to false). It releases all the previous savepoints as well.
con.rollback();This won't have any effect.
con.commit();Neither would this.
con.close();If all this code is in one block, there is no guarantee that the connection will be closed. This should be in a finally block preferably. :)