How it works...

The key code line in this recipe for JTA is as follows:

<persistence-unit name="ch02-jta-pu" transaction-type="JTA">

When you use transaction-type='JTA', you are saying to the server that it should take care of all transactions made under this context. If you use RESOURCE-LOCAL instead, you are saying that you are taking care of the transactions:

 @Test
 public void validTransaction() throws Exception{
     User user = new User(null, "Elder Moraes", 
     "elder@eldermoraes.com");
        
     userBean.add(user);
     user.setName("John Doe");
     userBean.update(user);
        
     User userDb = userBean.findById(1L);
     assertEquals(userDb.getName(), "John Doe");
        
 }

Each called method of UserBean starts a transaction to be completed and will run into a rollback if there's an issue while the transaction is alive. This would be committed to the end of it.