UnitOfWork (Google Guice 7.0.0 API)

```
public interface UnitOfWork
```
This interface is used to gain manual control over the unit of work. This is mostly to do work in non-request, non-transactional threads. Or where more fine-grained control over the unit of work is required. Starting and ending a unit of work directly corresponds to opening and closing a Session, EntityManager or ObjectContainer respectively.
The Unit of Work referred to by UnitOfWork will always be local to the calling thread. Be careful to end() in a finally block. Neither JPA, nor Hibernate supports threadsafe sessions (reasoning behind thread-locality of Unit of Work semantics).
- Using UnitOfWork with the PersistFilter inside a request is not recommended.
- Using UnitOfWork with session-per-txn strategy is not terribly clever either.
- Using UnitOfWork with session-per-request strategy but *outside* a request (i.e. in a background or bootstrap thread) is probably a good use case.

- Method Summary
  
  All Methods Instance Methods Abstract Methods
  Modifier and Type Method Description
  
  void begin()
  Starts a Unit Of Work.
  
  void end()
  Declares an end to the current Unit of Work.

- Method Detail
  - begin
```
void begin()
```
    Starts a Unit Of Work. Underneath, causes a session to the data layer to be opened. If there is already one open, the invocation will do nothing. In this way, you can define arbitrary units-of-work that nest within one another safely.
    Transaction semantics are not affected.
  - end
```
void end()
```
    Declares an end to the current Unit of Work. Underneath, causes any open session to the data layer to close. If there is no Unit of work open, then the call returns silently. You can safely invoke end() repeatedly.
    Transaction semantics are not affected.