Dependency injection when you only have one dependency

JavaZone

Johannes Brodwall, Recovering Spring User

Steria Norway

Let’s get rid ofdogmatic dependency

injection

Does this look familiar?

Person-Controller

Person-Controller-

Impl

Person-Service

Person-ServiceImpl

Person-Repository

Person-Repository

Impl

PersonDao

PersonDaoImpl

Session-Factory

Customer

Invoice

Order

Product

No more:

this.personService =new PersonServiceImpl(sessionFactory)

Instead:

<bean id="personDao" class=“…springmadness.dao.impl.PersonDaoImpl"> <property name="sessionFactory" …/></bean>

(Or)

@Autowired private PersonService personService;

Why?

Why?

(dear God, why?!)

Testing

Multiple implementations

Multiple implementations

(Really?)

Configuration

Configuration

(Often one)

Ordnung muss sein!

(Ordnung muss sein!)

Hobgoblin of little minds

- Ralph Waldo Emerson

Alternative

Session-Factory

PersonController

ServiceRepository

public class PersonController { private PersonService personService;

@Autowired public PersonController(SessionFactory sf) { this.personService = new PersonServiceImpl(sf); }

public class PersonController { private PersonService personService;

@Autowired public PersonController(SessionFactory sf) { this.personService = new PersonServiceImpl(sf); }

public class PersonServiceImpl implements … { private PersonRepository personRepo;

public PersonServiceImpl(SessionFactory sf) { this.personRepo = new PersonRepositoryImpl(sf); }

public class PersonController { private PersonService personService;

@Autowired public PersonController(SessionFactory sf) { this.personService = new PersonServiceImpl(sf); } public PersonControllerImpl(PersonService ps) { this.personService = ps; }

public class PersonController { private PersonService personService;

@Autowired public PersonController(SessionFactory sf) { this.personService = new PersonServiceImpl(sf); } public PersonControllerImpl(PersonService ps) { this.personService = ps; }

For Spring

For mocking

SPRING!

Session-Factory

PersonController

ServiceRepository

InvoiceController

Repository

FooServiceImpl

ReportsController

FooController

Look ma!No Spring!

Session-Factory

PersonServlet

Locator(singleton O_O)

”Injected” by servlet

public class PersonController extends HttpServlet { private PersonService personService; public PersonController() { } public PersonController(PersonService personService) { this.personService = personService; } @Override public void init() throws ServletException { SessionFactory sf = HibernateLookup.getInstance(getServletContext()); this.personService = new PersonServiceImpl(sf); }

public class PersonController extends HttpServlet { private PersonService personService; public PersonController() { } public PersonController(PersonService personService) { this.personService = personService; } @Override public void init() throws ServletException { SessionFactory sf = HibernateLookup.getInstance(getServletContext()); this.personService = new PersonServiceImpl(sf); }

For mocking

Look, ma! No Spring!

Session-Factory

PersonController

ServiceRepository

InvoiceController

Repository

FooServiceImpl

ReportsController

FooController

<<locator injection>>

<<locator injection>>

<<locator injection>>

<<locator in

jection>>

Bonus: Generic Repository

public interface Repository {

<T> T retrieve(Class<T> type,Serializable id);

Serializable save(Object object);

<T> List<T> find(Specification<T> spec);

Transaction beginTransaction();}

@RunWith(RepositoryTestRunner.class)public class PersonControllerTest { private Repository repository; private PersonController personController; public PersonControllerTest(Repository repo) { this.repository = repo; this.personController = new PersonController(repo); }

@Testpublic void should_show_person() { Person person = new Person(); Long id = (Long) repository.save(person); ModelAndView show = personController.show(id); assertEquals(person, show.getModel().get("person"));}

public class RepoTestRunner extends Suite { public RepoTestRunner(Class<?> testClass) { super(testClass, createRunners(testClass)); } static List<Runner> createRunners(Class<?> testClass) { List<Runner> runners = new ArrayList<Runner>();

runners.add(testRunner(testClass, new HashMapRepository())); if (!isRunningInInfinitest()) {

runners.add(testRunner(testClass, hibernateRepository())); } return runners; }

What Spring taught me

Be aware of dependencies!

Avoid differences between test and prod

Stay the heck away from frameworks!

Collapse service chains

Takk for meg!johannes.brodwall@steria.no

http://johannesbrodwall.com

http://sterkblanding.no

http://twitter.com/jhannes