Defining Spring Boot Java Beans

Defining Beans in Java Code

Creating a Bean with the @Bean Annotation

Hoge.java

package sample.springboot;

public class Hoge {

    private String name;

    public Hoge(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Hoge [name=" + name + "]";
    }
}

Main.java

package sample.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class Main {

    public static void main(String[] args) {
        try (ConfigurableApplicationContext ctx = SpringApplication.run(Main.class, args)) {
            Hoge h = ctx.getBean(Hoge.class);
            System.out.println(h);
        }
    }

    @Bean
    public Hoge getHoge() {
        System.out.println("Main#getHoge()");
        return new Hoge("hoge");
    }
}

Result

Main#getHoge()
Hoge [name=hoge]

Explanation

Annotate a method with @Bean to create a Bean instance through that method.
You can define this type of Bean in a class annotated with @Configuration.
- @SpringBootApplication has the same effect as applying @Configuration.

Creating a Separate Class Annotated with @Configuration

Annotate a class with @Configuration and a method with @Bean to define a method that creates a Bean of any class.

HogeProvider.java

package sample.springboot;

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

@Configuration
public class HogeProvider {

    @Bean
    public Hoge getHoge() {
        System.out.println("HogeProvider#getHoge()");
        return new Hoge("hoge provider");
    }
}

Main.java

package sample.springboot;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;

@SpringBootApplication
public class Main {

    public static void main(String[] args) {
        try (ConfigurableApplicationContext ctx = SpringApplication.run(Main.class, args)) {
            Hoge h = ctx.getBean(Hoge.class);
            System.out.println(h);
        }
    }
}

Result

HogeProvider#getHoge()
Hoge [name=hoge provider]