Transactions and security - EJB 3 in Action - page 240

to be instantiated directly and must be obtained from the container. Listing 6.4 used the
simplest way of getting a UserTransaction : injecting it through the @Resource an-
notation. There are a couple of other ways to do this: using JNDI lookups or through the
EJBContext .
JNDI lookups
The application server binds the UserTransaction to the JNDI name java:comp/
UserTransaction . You can look it up directly using JNDI with this code:
Context context = new InitialContext();
UserTransaction userTransaction = (UserTransaction)context.lookup("java:comp/
UserTransaction");
userTransaction.begin();
// Perform transacted tasks.
userTransaction.commit();
This method is typically used outside of EJBs—for example, if you need to use a transac-
tion in a helper or nonmanaged class in the EJB or web tier where dependency injection
isn't supported. If you find yourself in this situation, you might want to consider another
approach. It's much better to have that code in an EJB with greater access to abstractions.
EJBContext
You can also acquire a UserTransaction by invoking the getUserTransaction
method on EJBContext . This approach is useful if you're using a SessionContext
or MessageDrivenContext for some other purpose anyway, and a separate injection
to get a transaction instance would clutter the code. Note that you can use the getUser-
Transaction method only if you're using BMT. Calling this in a CMT environment will
cause the context to throw an IllegalStateException . The following code shows
the getUserTransaction method in action:
@Resource
private SessionContext context;
...
UserTransaction userTransaction = context.getUserTransaction();
userTransaction.begin();
// Perform transacted tasks...
userTransaction.commit();