Java Reference
In-Depth Information
entity. Recall that the
@Table
annotation specifies that the bid record should be saved in
tells JPA which
Bid
entity field maps to which column in the
BIDS
table. For example,
the
Id
property maps to the
BIDS.BID_ID
column, the
amount
property maps to the
BIDS.BID_AMOUNT
column, and so on. As we discussed earlier, the
@Id
and
@Gener-
atedValue
value annotations specify that the
BID_ID
column is the primary key of the
BIDS
table and that the JPA provider should automatically generate a value for the column
before the
INSERT
statement is issued (the
52
value in the SQL sample). This process of
translating an entity to columns in the database is exactly what O/R mapping and JPA is all
about.
In a similar vein to the
persist
method, the
find
method retrieves an entity by the
primary key, the
merge
method updates an entity in the database, and the
remove
meth-
od deletes an entity.
This brings us to the end of this brief introduction to the Java Persistence API—and to the
end of this whirlwind chapter. At this point, it should be clear to you how simple, effective,
and robust EJB 3 is, even from a bird's-eye view.
2.5. Summary
As we stated in the introduction, the goal of this chapter wasn't to feed you the “guru pill”
for EJB 3 but rather to show you what to expect from this new version of the Java Enter-
prise platform.
This chapter introduced the ActionBazaar application, a central theme to this topic. Using a
scenario from the ActionBazaar application, we showed you a cross-section of EJB 3 func-
tionality, including stateless session beans, stateful session beans, CDI, JSF 2, and JPA 2.
You learned some basic concepts such as metadata annotations, dependency injection, and
O/R mapping.
You used a stateless session bean to implement the business logic for placing a bid for an
item in an auctioning system. You then saw a stateful session bean that encapsulated the lo-
gic for ordering an item. You saw how EJB 3 components can be unit-tested via JUnit and
how JSF 2, CDI, and EJB 3 work together seamlessly across application tiers. Finally, we
