Testing JPA-based applications - JUnit in Action - page 361

Although discussing the different approaches is almost a religious matter, we
assume it's a good practice to abstract data persistence to specialized classes, such as
DAO s. The DAO s themselves can be implemented in many different ways:

Writing brute-force SQL statements (such as the UserDaoJdbcImpl example in
chapter 17)

■

Using third-party tools (like Apache i BATIS or Spring JDBC templates) that facil-
itate JDBC programming

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Delegating the whole database access to tools that map objects to SQL (and
vice-versa)

■

Over the last few years, the third approach has become widely adopted, through the
use of ORM (object-relational mapping) tools such as Hibernate and Oracle TopLink.
ORM became so popular that JCP (Java Community Process, the organization responsi-
ble for defining Java standards) created a specification 1 to address it, the JPA (Java Per-
sistence API ). JPA , as the name states, is just an API ; in order to use it, you need an
implementation. Fortunately, most existing tools adhere to the standard, so if you
already use an ORM tool (such as Hibernate), you could use it in JPA mode, that is,
using the Java Persistence API s instead of proprietary ones.
This chapter consists of two parts. First, we show how to test layers that use DAO s in
a multilayered application. Then we explain how to test the JPA -based DAO (data
access object) implementation, using DbUnit. 2
And although this chapter focuses on JPA and Hibernate, the ideas presented here
apply to other ORM tools as well.

18.1 Testing multilayered applications

By multilayered (or multitiered) application we mean an application whose structure
has been divided in layers, with each layer responsible for one aspect of the applica-
tion. A typical example is a three-tiered web application comprising of presentation,
business, and persistence layers.
Ideally, all of these layers should be tested, both in isolation (through unit tests)
and together (through integration tests). In this section, we show how to unit test the
business layer without depending on its lower tier, the persistence layer. But first, let's
look at the sample application.

18.1.1 The sample application

The examples in this chapter test the business and persistence layers (presentation
layer testing was covered in chapter 11) of an enterprise application. The persistence
layer comprises a User object and an UserDao interface, similar to those defined in

1

Some people may argue that two standards already existed before JPA: EJB entities and JDO. Well, EJB entities
were too complicated, and JDO never took off.

2

And in this aspect, this chapter is an extension of chapter 17; if you aren't familiar with DbUnit, we recom-
mend you read that chapter first.