Dependency injection

5.4.1. Dependency injection

Dependency injection (DI) is a process whereby objects define their dependencies, that is, the other object instance with, only through constructor arguments, arguments to a factory method, or properties that are set on the object instance after it is constructed or returned from a factory method.

DI exists in two major variants,

Constructor-based dependency injection

public class SimpleMovieListener {     // the simpleMovieListener has a dependency on a MovieFinder     private MovieFinder movieFinder;     // a constructor so that the Spring container can 'inject' a MovieFinder     public SimpleMovieListner(MovieFinder movieFinder) {         this.movieFinder = movieFinder;     // business logic that actually 'uses' the injected MovieFinder is omitted... }

Setter-based dependency injection

public class SimpleMovieListener {     // the simpleMovieListener has a dependency on the MovieFinder     private MovieFinder movieFinder;     // a setter method so that the Spring contaner can 'inject' a MovieFinder     public void setMovieFinder(MovieFinder movieFinder) {         this.movieFinder = movieFinder;     // business logic that actually 'uses' the injected MovieFinder is omitted... }

3. Dependency injection과 Spring Framework
객체 간의 의존 관계를 자신이 아닌 외부의 조립기가 수행해준다는 개념이다.

실제로 의존하는 객체를 지정하는 가장 간단한 방법은 코드에 직저접 명시하는 것이다.