Spring:Datenbanken

Codesnippets

    @Autowired
    private EntityManagerFactory entityManagerFactory;
    
    public Session getSession()
    {
        SessionFactory sessionFactory = entityManagerFactory.unwrap(SessionFactory.class);
        Session session = sessionFactory.openSession();
        return session;
    }
    
    @Test
    void whenCreateOneRule_thenItShouldBePossible()
    {
        Transaction tx = getSession().beginTransaction();
        // ...
        tx.commit();
    }

Set Up or Tear Down Outside of a Transaction

You can annotate a public void method with @BeforeTransaction or @AfterTransaction. This indicates to Spring that this method should be run before or after a test method is run within a transaction.

CGlib & JDK Proxies - @Transactional under the covers

Spring cannot really rewrite your Java class, like I did above, to insert the connection code (unless you are using advanced techniques like bytecode weaving, but we are ignoring that for now).

Your registerUser() method really just calls userDao.save(user), there’s no way to change that on the fly.

But Spring has an advantage. At its core, it is an IoC container. It instantiates a UserService for you and makes sure to autowire that UserService into any other bean that needs a UserService.

Now whenever you are using @Transactional on a bean, Spring uses a tiny trick. It does not just instantiate a UserService, but also a transactional proxy of that UserService.

It does that through a method called proxy-through-subclassing with the help of the Cglib library. There are also other ways to construct proxies (like Dynamic JDK proxies), but let’s leave it at that for the moment.

Let’s see proxies in action in this picture:

As you can see from that diagram, the proxy has one job.

• Opening and closing database connections/transactions.
• And then delegating to the real UserService, the one you wrote.
• And other beans, like your UserRestController will never know that they are talking to a proxy, and not the real thing.

Quellen: