Spring 5.3.21+ - Date : August 2022

What is Spring ?

• Open source (Apache 2 licence, sources on github)
• Light
  • Doesn't force to use an application server
  • Not invasive
• Container
  • Application objects doesn't have to look for their dependencies
  • Handles objects life cycle
• Framework
  • Ease integration and communication with third-party libraries

Minimal dependencies

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
</dependency>

Application configuration

• Java
• Annotations
• XML (still available but heavy)

@ComponentScan("fr.sii.cheatsheet.spring")
public class MyApp {

    public static void main(String[] args) {
        ApplicationContext app = new AnnotationConfigApplicationContext(MyApp.class);

        DummyService helloWorld = app.getBean(DummyService.class);
        helloWorld.getMessage();
    }
}

Prefer use of a configuration class

@Configuration
public class MyAppConfig {
  // @Bean, ...
}

Dependency injection

Define a bean : @Bean

@Configuration
public class MyAppConfig {
  @Bean
  public DummyService dummyService(){
    return new DummyServiceImpl();
  }
}

Define a bean : @Component

@Component specializations :

• @Service : Heart of an app
• @Repository : Handles data persistence
• @Controller : Handles requests and reponses

@Component
public class DummyServiceImpl implements DummyService {
}

Dependency injection : @Autowired

• Via a class field
• Via a setter
• Via the constructor (prefer for easy test)

@Component
public class FooServiceImpl implements FooService {

  @Autowired
  private DummyService service;
  
  @Autowired
  public FooServiceImpl(DummyService dummyservice) {
    this.service = dummyService;
  }
  
  @Autowired
  public DummyService setDummyService(DummyService dummyService) {
    this.service = dummyService;
  }

}