Stand-alone JPA and entityManager

Question

I found sth like this:

• 1 "If JPA is use stand-alone, you use EntityTransaction to demarcate the transaction yourself."
• 2 "If JPA is used within a managed environment where it integrates with JTA, you use UserTransaction"

My questions are:

• 1 What does it exactly mean that JPA is used stand-alone (it means that there is no managing environment like a container such as Java EE or Spring)?
• 2 What is transaction demarcation ?
• 3 Can spring be responsible for managing JPA (Spring is also a container so can we consider Spring to be a managed environment)?

Answer 1

Answers:

1. Standalone means more things, like: you create by your own instances of EntityManager (vs. they are not injected), you begin and commit by yourself transactions, you are responsible for propagating the transaction (which code (e.g of different services) gets executed in which transaction).

2. Transaction demarcation is the way you start, propagate and end the transaction. If you use a managed environment (with JTA), then you can annotate the service methods somehow and control how the "transaction is propagated" between different service calls. Say: with only annotations you can decide that on calling PersService.addPerson(Person person) a transaction T1 automatically is begun, and that code executed in AddressService.saveAddress(Address address) (called from addPerson()) is executed in the same transaction T1 (or if you want, a new transaction T2). Also with JTA, different databases can do work within the same transaction.

3. Yes, Spring can be and is almost always configured to work as a managed environment. But it can be configured to work also in a standalone mode. Other known managed environments are the Java EE enviroments (Application servers like WildFly or Glassfish).