save() method can return that primary key id value which is generated by hibernate and we can see it by
long s = session.save(k);
In this same case, persist() will never give any value back to the client, hope you are clear.
When to use Persist() and when to use save() ?
persist() is well defined. It makes a transient instance persistent. However, it doesn’t guarantee that the identifier value will be assigned to the persistent instance immediately, the assignment might happen at flush time. The spec doesn’t say that, which is the problem I have with persist().
persist() also guarantees that it will not execute an INSERT statement if it is called outside of transaction boundaries. This is useful in long-running conversations with an extended Session/persistence context.
A method like persist() is required.
save() does not guarantee the same, it returns an identifier, and if an INSERT has to be executed to get the identifier (e.g. “identity” generator, not “sequence”), this INSERT happens immediately, no matter if you are inside or outside of a transaction. This is not good in a long-running conversation with an extended Session/persistence context.