Threads and transactions

I have a quick question about threads and transactions.

Does the J2EE spec guarantee a single thread per transaction? That is, during the course of a transction, can the execution of the transaction switch to a different thread?

If a single thread is guaranteed for a transaction, does that hold true when a transaction encompasses calls between applications deployed in different ears on the same JVM (container)?

Thanks!

The J2EE spec. guarentees nothing about threads, whether in a transaction or not, other than they are the sole responsibility of the container. So you should not have to worry about them at all.