Spring @Lazy Annotation Example

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In this short article, we’ll discuss Spring’s @Lazy annotation with an example.
 
By default, the Spring IoC container creates and initializes all singleton beans at application startup. However, we can prevent this pre-initialization by using the @Lazy annotation.
 
The @Lazy annotation may be used in any class directly or indirectly annotated with @Component or in methods annotated with @Bean. 

YouTube Video - Spring @Lazy Annotation

In this example, we will use a Java-based configuration(using @Configuration and @Bean). 

Spring @Lazy Annotation Example

Let's create an example to demonstrate using @Lazy annotation in a spring application.

Create a Simple Maven Project

Create a simple Maven project using your favourite IDE. Refer to the section below for the packaging structure. If you are new to Maven, read the article How to Create a Simple Maven Project.

Project Structure

The below diagram shows a project structure for your reference -

Maven Dependency

Note that Spring Framework 6 requires Java 17 or later version:
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>6.1.8</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>6.1.8</version>
        </dependency>

Create Spring Beans - FirstBean and SecondBean

FirstBean.java 
package net.javaguides.spring.lazy;

public class FirstBean {

    public FirstBean() {
        System.out.println("Inside FirstBean Constuctor");
    }

    public void test() {
        System.out.println("Method of FirstBean Class");
    }
}
SecondBean.java 
package net.javaguides.spring.lazy;

public class SecondBean {

    public SecondBean() {
        System.out.println("Inside SecondBean Constuctor");
    }

    public void test() {
        System.out.println("Method of SecondBean Class");
    }
}

Java-Based Configuration - AppConfig.java

Declare the above beans in the Java-based configuration class.
package net.javaguides.spring.lazy;

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

@Configuration
public class AppConfig {

    @Lazy(value = true)
    @Bean
    public FirstBean firstBean() {
        return new FirstBean();
    }

    @Bean
    public SecondBean secondBean() {
        return new SecondBean();
    }
}

Running Spring Application - Application.java

Let's create a main class and run an application. 
package net.javaguides.spring.lazy;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class Application {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        FirstBean firstBean = context.getBean(FirstBean.class);
        firstBean.test();
        context.close();
    }
}
Output:
Inside SecondBean Constuctor
Inside FirstBean Constuctor
Method of FirstBean Class
As we can see, bean secondBean is initialized by the Spring container while bean firstBean is initialized explicitly.
The source code of this article is available on my GitHub repository https://github.com/RameshMF/spring-core-tutorial

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