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Lazy-initialized Beans

By default, ApplicationContext implementations eagerly create and configure all singleton beans as part of the initialization process. Generally, this pre-instantiation is desirable, because errors in the configuration or surrounding environment are discovered immediately, as opposed to hours or even days later. When this behavior is not desirable, you can prevent pre-instantiation of a singleton bean by marking the bean definition as being lazy-initialized. A lazy-initialized bean tells the IoC container to create a bean instance when it is first requested, rather than at startup.

This behavior is controlled by the @Lazy annotation or in XML the lazy-init attribute on the <bean/> element, as the following example shows:

Java
Kotlin
Xml

@Bean
@Lazy
ExpensiveToCreateBean lazy() {
	return new ExpensiveToCreateBean();
}

@Bean
AnotherBean notLazy() {
	return new AnotherBean();
}

@Bean
@Lazy
fun lazy(): ExpensiveToCreateBean {
	return ExpensiveToCreateBean()
}

@Bean
fun notLazy(): AnotherBean {
	return AnotherBean()
}

<bean id="lazy" class="com.something.ExpensiveToCreateBean" lazy-init="true"/>

<bean name="notLazy" class="com.something.AnotherBean"/>

When the preceding configuration is consumed by an ApplicationContext, the lazy bean is not eagerly pre-instantiated when the ApplicationContext starts, whereas the notLazy one is eagerly pre-instantiated.

However, when a lazy-initialized bean is a dependency of a singleton bean that is not lazy-initialized, the ApplicationContext creates the lazy-initialized bean at startup, because it must satisfy the singleton’s dependencies. The lazy-initialized bean is injected into a singleton bean elsewhere that is not lazy-initialized.

You can also control lazy-initialization for a set of beans by using the @Lazy annotation on your @Configuration annotated class or in XML using the default-lazy-init attribute on the <beans/> element, as the following example shows:

Java
Kotlin
Xml

@Configuration
@Lazy
public class LazyConfiguration {
	// No bean will be pre-instantiated...
}

@Configuration
@Lazy
class LazyConfiguration {
	// No bean will be pre-instantiated...
}

<beans default-lazy-init="true">

	<!-- No bean will be pre-instantiated... -->
</beans>