Spring Boot @Bean Annotation Example

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 In this tutorial, we will learn everything about Spring Boot @Bean annotation with examples.

@Bean Annotation Overview

The @Bean annotation indicates that a method produces a bean to be managed by the Spring container. 

The @Bean annotation is usually declared in the Configuration class to create Spring Bean definitions.

YouTube Video - @Bean Annotation

@Bean Annotation Example

In order to demonstrate the usage of @Bean annotation, let's create a couple of Java classes.

Student and Address

class Student{ private Address address; public Student(Address address){ this.address = address; } public void print(){ System.out.println("Student class method called ..."); address.print(); } } class Address{ public void print(){ System.out.println("Address class method called ..."); } }

AppConfig Class

Next, let's create a Java configuration class annotated with @Configuration annotation. Within this class, let's create bean definitions using @Bean annotation.

@Configuration class AppConfig{ @Bean public Address address(){ return new Address(); } @Bean public Student student(){ return new Student(address()); } }

Bean Names

By default, the bean name is the same as the method name. We can specify the bean names using @Bean(name = “beanName”).

For example:

 @Bean(name = "addressBean") public Address address(){ return new Address(); } @Bean(name = "studentBean") public Student student(){ return new Student(address()); }

Define Mulitple Bean Names

We can also specify multiple names for a single Spring bean. 

For example:

 @Bean(name = {"studentBean", "studentDemo", "studentComponent"}) public Student student(){ return new Student(address()); }

Next, we can retrieve the student Spring bean object using any of these bean names. For example:

Student student = (Student) applicationContext.getBean("studentBean");

Or 

Student student = (Student) applicationContext.getBean("studentDemo");

Or 

Student student = (Student) applicationContext.getBean("studentComponent");

@Bean initMethod and destroyMethod attributes

@Bean annotation provides initMethod and destroyMethod attributes to perform certain actions after bean initialization or before bean destruction by a container.

For example, the Student Spring bean has initMethod and destroyMethod attributes:

@Configuration class AppConfig{ @Bean(name = "addressBean") public Address address(){ return new Address(); } @Bean(name = "studentBean", initMethod = "init", destroyMethod = "destroy") public Student student(){ return new Student(address()); } }

Next, create init() and destroy() methods in Student class:

class Student{ private Address address; public Student(Address address){ this.address = address; } public void print(){ System.out.println("Student class method called ..."); address.print(); } public void init(){ System.out.println("Intialization logic"); } public void destroy(){ System.out.println("Destruction logic"); } }

Testing

Run the below code to test all the @Bean annotation use cases:

public class BeanAnnotationDemo { public static void main(String[] args) { try(var applicationContext = new AnnotationConfigApplicationContext(AppConfig.class)){ //Student student = applicationContext.getBean(Student.class); Student student = (Student) applicationContext.getBean("studentBean"); String[] beanNames = applicationContext.getBeanDefinitionNames(); for (String bean: beanNames){ System.out.println(bean); } student.print(); } } }

Complete Code

Here is the complete code for your reference:

package com.spring.core.beans; import org.springframework.context.annotation.AnnotationConfigApplicationContext; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; class Student{ private Address address; public Student(Address address){ this.address = address; } public void print(){ System.out.println("Student class method called ..."); address.print(); } public void init(){ System.out.println("Intialization logic"); } public void destroy(){ System.out.println("Destruction logic"); } } class Address{ public void print(){ System.out.println("Address class method called ..."); } } @Configuration class AppConfig{ @Bean(name = "addressBean") public Address address(){ return new Address(); } @Bean(name = "studentBean", initMethod = "init", destroyMethod = "destroy") public Student student(){ return new Student(address()); } } public class BeanAnnotationDemo { public static void main(String[] args) { try(var applicationContext = new AnnotationConfigApplicationContext(AppConfig.class)){ //Student student = applicationContext.getBean(Student.class); Student student = (Student) applicationContext.getBean("studentBean"); String[] beanNames = applicationContext.getBeanDefinitionNames(); for (String bean: beanNames){ System.out.println(bean); } student.print(); } } }

Conclusion

 In this tutorial, we have seen how to use @Bean annotation to create and manage Spring bean by Spring container. We have also seen how to use initMethod and destroyMethod attributes of @Bean annotation.

Related Spring and Spring Boot Annotations

• Spring Boot @Bean Annotation Example
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