Bean, Inversion of Control, Dependency Injection

 * Bean - object-dir. Spring terefinden idare oluna bilen bir object. 

Bean scopes:

singleton

prototype

request

session

application

websocket

Define Bean: 1) @Bean 2) stereotype annotation -> @Controller, @RestController,  @Service, @Repository, @Component

* Inversion of Control: IoC Container

package com.example.burhan_lesson_1.config;

import com.example.burhan_lesson_1.UserService;
import com.example.burhan_lesson_1.UserServiceImpl;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class BeanConfig {

    @Bean
    public UserService userServiceImpl() {
        return new UserServiceImpl();
    }
}

Tutaq ki biz bu wekilde class yaratdiqda ve @Configuration iwletdikde o zaman IoC Containerde:

UserService userService = UserServiceImpl(); bir object yaranir.

* @Qualifier: eger bir interface-in birden cox implementasiyasi varsa biz bu annotation-u istifade ede bilerik.

package com.example.burhan_lesson_1;

import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Controller;

@Controller
public class UserController {

    private final UserService userService;

    public UserController(@Qualifier("userServiceImpl2") UserService userService) {
        this.userService = userService;
    }

    public void foo() {
        userService.demo();
    }
}

Injectionun 3 tipi var: 1) Constuctor base injectin   2) Field type injection   3) Setter base injection

 Constuctor base injection:

 package com.example.burhan_lesson_1;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class BurhanLesson1Application implements CommandLineRunner {

    private final UserController userController;

    @Autowired
    public BurhanLesson1Application(UserController userController) {
        this.userController = userController;
    }

//    @Autowired
//    public UserController userController;

    public static void main(String[] args) {
        SpringApplication.run(BurhanLesson1Application.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
//        UserService userService = new UserServiceImpl();
//        UserController userController = new UserController(userService);
        userController.foo();
    }
}

Field type injection:

 package com.example.burhan_lesson_1;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class BurhanLesson1Application implements CommandLineRunner {

//    private final UserController userController;
//
//    @Autowired
//    public BurhanLesson1Application(UserController userController) {
//        this.userController = userController;
//    }

    @Autowired
    public UserController userController;

    public static void main(String[] args) {
        SpringApplication.run(BurhanLesson1Application.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
//        UserService userService = new UserServiceImpl();
//        UserController userController = new UserController(userService);
        userController.foo();
    }
}

Field type injection yalniz cagrilan zaman IoC-den gedib cagrilib inject olunacaq.

Setter type injection:

 package com.example.burhan_lesson_1;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class BurhanLesson1Application implements CommandLineRunner {

//    private final UserController userController;
//
//    @Autowired
//    public BurhanLesson1Application(UserController userController) {
//        this.userController = userController;
//    }

//    @Autowired
//    public UserController userController;

    private UserController userController;

    @Autowired
    public void setUserController(UserController userController) {
        this.userController = userController;
    }

    public static void main(String[] args) {
        SpringApplication.run(BurhanLesson1Application.class, args);
    }

    @Override
    public void run(String... args) throws Exception {
//        UserService userService = new UserServiceImpl();
//        UserController userController = new UserController(userService);
        userController.foo();
    }
}

* Constuctor base injection ustunluyu ondan ibaretdir ki, application qalxan zaman butun beanlari inject edir.