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Spring Boot @Bean @Component 違い

Posted at

どちらで登録するオブジェクトもSpringコンテナに登録される

Bean(カスタムしたインスタンスを登録)

CustomGreeting.java
// 引数つきコンストラクタを勝手に生成してくれるアノテーション
@AllArgsConstructor
public class CustomGreeting {
	private final String name;
	private final String words;

	public void greeting() {
		System.out.println(words + name + "さん");
	}
}

カスタムインスタンスをBean登録

BeanConfiguration.java
@Configuration
public class BeanConfiguration {

	@Bean
	CustomGreeting greetTanaka() {
		return new CustomGreeting("田中", "こんにちは");
	}

	@Bean
	CustomGreeting greetJohn() {
		return new CustomGreeting("John", "hi");
	}

}

Component(クラスのインスタンスが登録される)

BeanSample.java
@Component
public class BeanSample {

	public void hello() {
		System.out.println("hello");
	}

}

実行

SampleApplication.java
@SpringBootApplication
public class SampleApplication {

	public static void main(String[] args) {
		ConfigurableApplicationContext context = SpringApplication.run(SampleApplication.class, args);
		BeanSample bean = context.getBean(BeanSample.class);
		bean.hello();

		CustomGreeting greetTanaka = (CustomGreeting) context.getBean("greetTanaka");
		greetTanaka.greeting();

		CustomGreeting greetJohn = (CustomGreeting) context.getBean("greetJohn");
		greetJohn.greeting();

		context.close();
	}

}

hello
こんにちは田中さん
hiJohnさん

Beanで登録したオブジェクトを引数に

登録されるクラス

Yuusha.java
@AllArgsConstructor
public class Yuusha {
	private String name;
	private Mahou mahou;
	
	public void attack() {
		System.out.println("勇者" + name + "の攻撃");
		mahou.hatudou();
	}
}

引数で登録するクラス

Mahou.java
@AllArgsConstructor
public class Mahou {
	private String zokusei;
	private int count;

	public void hatudou() {

		if (count-- >= 0) {
			System.out.println(zokusei + "を発動しました");
		} else {
			System.out.println("MPがありません");
		}

	}
}

Beanを登録

BeanConfiguration.java
@Configuration
public class BeanConfiguration {

	@Bean
	Yuusha yuushaYoshida(Mahou fire) {
		return new Yuusha("Yoshida", fire);
	}

	@Bean
	Mahou fire() {
		return new Mahou("ふぁいあー", 3);
	}

    // 適当なBeanも登録しておく
	@Bean
	Mahou kaminari() {
		return new Mahou("かみなり", 3);
	}

}

実行

SampleApplication.java
@SpringBootApplication
public class SampleApplication {

	public static void main(String[] args) {
		ConfigurableApplicationContext context = SpringApplication.run(SampleApplication.class, args);
		BeanSample bean = context.getBean(BeanSample.class);

		Yuusha yuushaYoshida = (Yuusha) context.getBean("yuushaYoshida");
		yuushaYoshida.attack();
		yuushaYoshida.attack();
		yuushaYoshida.attack();
		yuushaYoshida.attack();
		yuushaYoshida.attack();

		context.close();
	}

}

しっかりfireが登録されている

勇者Yoshidaの攻撃
ふぁいあーを発動しました
勇者Yoshidaの攻撃
ふぁいあーを発動しました
勇者Yoshidaの攻撃
ふぁいあーを発動しました
勇者Yoshidaの攻撃
ふぁいあーを発動しました
勇者Yoshidaの攻撃
MPがありません
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