Understanding Lazy Initialization in Spring Boot
Tags: springboot, java, lazyloading, lazyannotation
Published: 2024-06-26 09:38:11

In this blog, we'll explore the concept of lazy initialization in Spring Boot, how to use the "@ Lazy" annotation, and the benefits it can bring to your applications.

## What is Lazy Initialization?

Lazy initialization is a design pattern which delays the creation of an object until it is really needed. In the context of Spring, it means that a bean is not instantiated and initialized until it is first requested. This can be particularly useful for improving the startup time of an application, especially if there are many beans or if some beans are resource-intensive to create.

## The "@ Lazy" Annotation

Spring provides the "@ Lazy" annotation to enable lazy initialization. This annotation can be used in several ways:

**1. Using @ Lazy on Bean Definitions**

To use "@ Lazy" on a bean definition, simply annotate the bean method with "@ Lazy". 

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

@Configuration
public class AppConfig {

    @Bean
    @Lazy
    public TestBean testBean() {
        return new testBean();
    }
}
```
In this example, "testBean" will not be created until it is first requested.

**2. Using @ Lazy on Configuration Classes**

You can also apply "@ Lazy" at the class level to indicate that all beans within the configuration should be lazily initialized.

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

@Configuration
@Lazy
public class LazyConfig {

    @Bean
    public TestBean testBean() {
        return new TestBean();
    }

    @Bean
    public AnotherTestBean anotherTestBean() {
        return new AnotherTestBean();
    }
}
```
In this case, both "testBean" and "anotherTestBean" will be lazily initialized.

**3. Using @Lazy on Dependencies**

You can use "@ Lazy" on a field or method parameter to lazily resolve the dependency.

```
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Lazy;
import org.springframework.stereotype.Component;

@Component
public class TestComponent {

    private final TestBean testBean;

    @Autowired
    public TestComponent(@Lazy TestBean testBean) {
        this.testBean = testBean;
    }

    // you can include other methods here
}
```
Here, "testBean" will only be created when it is first accessed in "TestComponent".

## Benefits of Lazy Initialization

- **Improved Startup Time**: By deferring the creation of beans until they are needed, the initial startup time of the application can be reduced.

- **Resource Management**: Lazy initialization can help manage resources more efficiently by only instantiating beans that are actually used.

- **Avoiding Circular Dependencies**: Lazy initialization can help break circular dependencies by delaying the creation of beans.

## Conclusion

By using the "@ Lazy" annotation, you can control when beans are instantiated and initialized. However, it's important to use this feature carefully and be aware of its potential impact on application performance.

## References

https://www.baeldung.com/spring-lazy-annotation

https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/annotation/Lazy.html

**Github** : https://github.com/tharindu1998/lazy-annotation