@Configuration and @Bean

Definition

A @Configuration class contains @Bean methods, and each method describes one bean. It is the way to register objects you do not own (such as a library class) and to wire beans together in plain Java code.

Example code

Beans that depend on each other, wired in Java

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

record DatabaseConfig(String url) { }

class OrderRepository {
    final DatabaseConfig config;
    OrderRepository(DatabaseConfig config) { this.config = config; }
}

@Configuration
class AppConfig {
    @Bean
    DatabaseConfig databaseConfig() { return new DatabaseConfig("jdbc:h2:mem:shop"); }

    @Bean
    OrderRepository orderRepository(DatabaseConfig config) {       // Spring passes the other bean in
        return new OrderRepository(config);
    }
}

class Demo {
    public static void main(String[] args) {
        try (var context = new AnnotationConfigApplicationContext(AppConfig.class)) {
            System.out.println(context.getBean(OrderRepository.class).config.url());
        }
    }
}

// Output:
// jdbc:h2:mem:shop