Introducing I.O.C
Give the container the keys, he’ll give you flexibility
Dependency Injection
The container creates, provides and destroys the components
careful with
newfor components in the code.@Bean/@Produces: Method used for building complex beans of a given type@Autowired/@Inject: Where to inject what (attribute, parameter)@Scope: Life of beans (singleton, request, prototype, etc.)
DI : Behind the "magic"
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Manage them all : The framework launches the application to manage everything
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Wrap them all : Wrappers (proxies, decorators, facades) are injected rather than our actual objects
DI : Design for it
Composition over inheritance
Advantages of IOC
Automatic DAO / DAL
@Entity public class User { @ID String email; String firstname; String lastname; }Basic operations on repositories are very simple to code
public interface UserRepository extends CrudRepository<User, String> { Page<User> findByFirstnameAndLastname(String fname, String lname, Pageable pageable); }
Advantages of IOC
Transport code is transparent
@RestContoller public class UserContoller { @Autowired protected UserRepository repository; @GetMapping("/users") public Page<User> findUsers( @QueryParam("firstname") String firstname, @QueryParam("lastname") String lastname, Pageable pageable) { return repository .findByFirstnameAndLastname(firstname, lastname, pageable); } }
Common errors
can only inject what is known : careful with
newcan only inject into what is known
default scope is
singletonrequestscope is stored onThreadLocal: careful with parallel streams in Java 8+