[`Connection.setTransactionIsolation(int)`](http://download.oracle.com/javase/6/docs/api/java/sql/Connection.html#setTransactionIsolation%28int%29) warns:

> 
> Note: If this method is called during a transaction, the result is implementation-defined. 
> 
> 
> 

This bring up the question: **how do you begin a transaction in JDBC?** It's clear how to end a transaction, but not how to begin it.

If a `Connection` starts inside in a transaction, how are we supposed to invoke `Connection.setTransactionIsolation(int)` outside of a transaction to avoid implementation-specific behavior?