Spring Annotation-Based Bean Registration Guide

This article introduces how to register components in Spring using annotations.

@Configuration and @Bean

Defines a configuration class and registers a bean via a @Bean method. Example bean class Dog and XML configuration are shown, then the annotation‑based equivalent.

public class Dog {
    private String name;
    private int age;
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
    public int getAge() { return age; }
    public void setAge(int age) { this.age = age; }
    @Override
    public String toString() { return "Dog [name=" + name + ", age=" + age + "]"; }
}

@Configuration
public class MyConfig {
    @Bean
    public Dog dog() {
        Dog dog = new Dog();
        dog.setName("Tom");
        dog.setAge(5);
        return dog;
    }
}

Using AnnotationConfigApplicationContext to obtain the bean.

ApplicationContext ctx = new AnnotationConfigApplicationContext(MyConfig.class);
Dog dog = (Dog) ctx.getBean("tomDog");
System.out.println(dog);

@ComponentScan

Scans packages to auto‑detect @Component , @Service , @Repository , @Controller . Example:

@Configuration
@ComponentScan("com.wwj")
public class MyConfig { }

Shows includeFilters, excludeFilters, useDefaultFilters, custom TypeFilter , etc.

@ComponentScan(value = "com.wwj", excludeFilters = {
    @Filter(type = FilterType.ANNOTATION, classes = { Controller.class, Service.class })
})
public class MyConfig { }

@Scope

Specifies bean scope (prototype, singleton, request, session).

@Scope("prototype")
@Bean
public Dog dog() {
    Dog dog = new Dog();
    dog.setName("Tom");
    dog.setAge(5);
    return dog;
}

@Lazy

Enables lazy initialization of a bean.

@Lazy
@Bean
public Dog dog() {
    Dog dog = new Dog();
    dog.setName("Tom");
    dog.setAge(5);
    return dog;
}

@Conditional

Registers a bean only when a custom condition matches.

@Conditional(MyCondition.class)
@Bean
public Dog dog() {
    Dog dog = new Dog();
    dog.setName("Tom");
    dog.setAge(5);
    return dog;
}

@Import

Directly imports a class or selector into the context.

@Configuration
@Import(Dog.class)
public class MyConfig { }

@Import(MyImportSelector.class)
public class MyConfig { }

@FactoryBean

Creates beans via a FactoryBean implementation.

public class DogFactoryBean implements FactoryBean
{
    @Override
    public Dog getObject() throws Exception { return new Dog(); }
    @Override
    public Class
getObjectType() { return Dog.class; }
    @Override
    public boolean isSingleton() { return true; }
}

@Configuration
public class MyConfig {
    @Bean
    public DogFactoryBean dogFactoryBean() {
        return new DogFactoryBean();
    }
}

The article concludes that these annotations simplify bean registration compared with XML configuration.