CODEWITHSUNDEEP
spring
PowerFlower
PowerFlower

Reputation: 1619

Receiving Objects from the IoC Container - Spring

have have these two apps which actually do the same (if I am correct)

@SpringBootApplication
public class DemoApplication {

    @Autowired
    HelloWorld helloWorld;

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

    @Bean
    public CommandLineRunner run() {
        helloWorld.setMessage("wow");
        return (load) -> {
            helloWorld.getMessage();
        };
    }
}

and

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new 
      ClassPathXmlApplicationContext("Beans.xml");
      HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
      obj.getMessage();
   }
}

both uses 

    @Component
   public class HelloWorld {
    private String message;

    public void setMessage(String message) {
        this.message = message;
    }

    public void getMessage() {
        System.out.println("Your Message : " + message);
    }
}

The only difference at the helloWord obj is, that if I use the MainApp-class in my program, then the helloWorld class doesn't need the @Component annotation.

My Question:

If I am correct the SpringBoot annotation makes it unnecessary to define a ClassPathXMLApplicationContext. @Autowire does that for me.

I am now interested if I AutoWire lets say 100 objects at the beginning, all these objects are now in the IoC container correct?

If so: Is not possible to just hand out that container in a CTOR of another class and have access to all saved objects there like: (HelloWorld) context.getBean("helloWorld"); or (someRandomClass) context.getBean("someRandomClass")

    public CTOR(IOCContainer container) {
    this.container = container;
}

Instead of that implementation

  public CTOR(HelloWorld helloWorld, SomeRandomClass someRandomClass) {
        this.helloWorld = helloWorld;
        this.someRandomClass = someRandomClass;
    }

And if that is possible, how can I do that? (There is no use case/task behind my question, i am just interested if that is possible)

Upvotes: 1

Views: 985

Answers (2)

Praneeth Ramesh
Praneeth Ramesh

Reputation: 3564

There are two ways of creating beans in Spring. One is through XML config and the other is through annotation config. Annotation config is the preferred approach as it has lot of advantages over xml config.

Spring boot doesnt have any thing to do with annotation or xml config. Its just a easy way to boot spring application. @Component creates the object of the annotated bean in the application context. @Import or @ImportResource are the annotations used to load the configs from Annotations or through XML configs in Spring boot. With Spring boot u need not create ClassPathXMlCOntext or AnnotationContext objects, but its created internally by spring boot.

@Autowired is a way of getting the beans into any object by injecting rather than tight coupling to the code. Spring container(Application context) do this job of injecting. Just autowiring any class wont create the objects in Spring context. Its just an indication for the Spring context to set the object in the Application context here. You need to create them explicitly inside a xml config/ or annotations like @Component @Service others.

There is no need of hand out of container anywhere. U can just @Autowire ApplicationContext context; in any other spring bean object. With which you can call getBean(YourBean.class) to get that bean.

Upvotes: 2

Peter
Peter

Reputation: 793

The XML'ish way of configuration where you define your bean and wiring via

<bean ... etc. pp.

can be completely replaced by either using

@Component
public class MyClass ....

or by 

@Bean
public MyClass myClass() {return new MyClass();}

definition in a configuration class. Both ways place the entity in the IoC container of Spring.

The @Autowire just informs the IoC container of Spring that you would like to have a bean fulfilling the contract of the entity marked with @Autowire injected into this place.

In order to get access to the container you just need to inject the ApplicationContext where you would like to have it.

Upvotes: 2

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