How to Register Beans in the Spring Container: Five Common Methods

The author, a senior architect, introduces the question of how to put a bean into the Spring container and promises to summarize the common approaches.

1. @Configuration + @Bean – Declare a configuration class with @Configuration and expose a bean via a @Bean method.

@Configuration
public class MyConfiguration {
    @Bean
    public Person person() {
        Person person = new Person();
        person.setName("spring");
        return person;
    }
}

2. @Component + @ComponentScan – Mark a class with @Component and enable scanning with @ComponentScan on a configuration class.

@Component
public class Person {
    private String name;
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    @Override
    public String toString() { return "Person{name='" + name + "'}"; }
}

@ComponentScan(basePackages = "com.springboot.initbean.*")
public class Demo1 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);
        Person bean = applicationContext.getBean(Person.class);
        System.out.println(bean);
    }
}

3. @Import – Four usage patterns:

Direct class import.

ImportSelector implementation.

ImportBeanDefinitionRegistrar implementation.

DeferredImportSelector implementation.

Import annotation definition:

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Import {
    Class
[] value();
}

Direct class import example:

public class Person {
    private String name;
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    @Override
    public String toString() { return "Person{name='" + name + "'}"; }
}

@Import(Person.class)
public class Demo1 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);
        Person bean = applicationContext.getBean(Person.class);
        System.out.println(bean);
    }
}

ImportSelector example:

@Import(MyImportSelector.class)
public class Demo1 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);
        Person bean = applicationContext.getBean(Person.class);
        System.out.println(bean);
    }
}

class MyImportSelector implements ImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{"com.springboot.pojo.Person"};
    }
}

ImportBeanDefinitionRegistrar example:

@Import(MyImportBeanDefinitionRegistrar.class)
public class Demo1 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);
        Person bean = applicationContext.getBean(Person.class);
        System.out.println(bean);
    }
}

class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Person.class).getBeanDefinition();
        registry.registerBeanDefinition("person", beanDefinition);
    }
}

DeferredImportSelector example (similar to ImportSelector but processed later):

@Import(MyDeferredImportSelector.class)
public class Demo1 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);
        Person bean = applicationContext.getBean(Person.class);
        System.out.println(bean);
    }
}

class MyDeferredImportSelector implements DeferredImportSelector {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{Person.class.getName()};
    }
}

4. FactoryBean – Implement FactoryBean to create bean instances programmatically.

@Configuration
public class Demo1 {
    @Bean
    public PersonFactoryBean personFactoryBean() {
        return new PersonFactoryBean();
    }
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext(Demo1.class);
        Person bean = applicationContext.getBean(Person.class);
        System.out.println(bean);
    }
}

class PersonFactoryBean implements FactoryBean
{
    @Override
    public Person getObject() throws Exception { return new Person(); }
    @Override
    public Class
getObjectType() { return Person.class; }
}

5. BeanDefinitionRegistryPostProcessor – Register bean definitions during container startup.

public class Demo1 {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
        MyBeanDefinitionRegistryPostProcessor beanDefinitionRegistryPostProcessor = new MyBeanDefinitionRegistryPostProcessor();
        applicationContext.addBeanFactoryPostProcessor(beanDefinitionRegistryPostProcessor);
        applicationContext.refresh();
        Person bean = applicationContext.getBean(Person.class);
        System.out.println(bean);
    }
}

class MyBeanDefinitionRegistryPostProcessor implements BeanDefinitionRegistryPostProcessor {
    @Override
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
        AbstractBeanDefinition beanDefinition = BeanDefinitionBuilder.rootBeanDefinition(Person.class).getBeanDefinition();
        registry.registerBeanDefinition("person", beanDefinition);
    }
    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {}
}

The article concludes with a concise list of the five methods and then includes promotional material for a ChatGPT community, giveaways, and various external links.