HowToDoInJava

Spring – Eager vs lazy loading

By | Filed Under: Core

By default, Spring “application context” eagerly creates and initializes all ‘singleton scoped‘ beans during application startup itself. It helps in detecting the bean configuration issues at early stage, in most of the cases. But sometimes, you may need to mark some or all beans to be lazy initialized due to different project requirements.

Spring provides two easy ways to configure lazy initialization of beans based on which kind of configuration you are employing i.e. XML based configuration or java based configuration.

Table of Contents

1. Lazy initialized beans in XML based configuration
2. Lazy initialized beans in Java based configuration

1. Lazy initialized beans in XML based configuration

1.1. Lazy load specific beans only

To enable lazy loading for specific beans, use lazy-init=”true” attribute on bean definitions in bean configuration xml files.

<beans>

<bean id="employeeManager" class="com.howtodoinjava.spring.service.impl.EmployeeManagerImpl" 
	lazy-init="true"/>

<beans>

1.2. Lazy load all beans globally

To enable lazy loading for all beans, use default-lazy-init=”true” attribute on beans tag in bean configuration xml files.

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

<bean id="employeeManager" class="com.howtodoinjava.spring.service.impl.EmployeeManagerImpl" />

<beans>

2. Lazy initialized beans in Java based configuration

2.1. Lazy load specific beans only

To lazy load only specific beans, use @Lazy annotation along with @Bean annotation in java config.

import org.springframework.context.annotation.Lazy;

@Configuration
public class AppConfig {
	
	@Lazy
	@Bean
    public EmployeeManager employeeManager() {
        return new EmployeeManagerImpl();
    }
	
}

2.2. Lazy load all beans

To lazy load all beans, use @Lazy annotation along with @Bean annotation in java config.

import org.springframework.context.annotation.Lazy;

@Lazy
@Configuration
public class AppConfig {
	
	@Bean
    public EmployeeManager employeeManager() {
        return new EmployeeManagerImpl();
    }
	
}

3. Demo

Let’s see the code of bean, we are trying to lazy load.

public class EmployeeManagerImpl implements EmployeeManager {

	@Override
	public Employee create() {
		Employee emp =  new Employee();
		emp.setId(1);
		emp.setName("Lokesh");
		return emp;
	}
	
	@PostConstruct
	public void onInit(){
		System.out.println("EmployeeManagerImpl Bean is Created !!");
	}
}

I have put the @PostConstruct annotation to detect when bean is created.

Lets initialize the application context with –

3.1. “Without Lazy loading” enabled

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

import com.howtodoinjava.spring.model.Employee;
import com.howtodoinjava.spring.service.EmployeeManager;

public class Main 
{
    public static void main( String[] args )
    {
    	ApplicationContext ctx = new AnnotationConfigApplicationContext(AppConfig.class);
    	
    	System.out.println("Bean Factory Initialized !!");
        
    	EmployeeManager empManager = ctx.getBean(EmployeeManager.class);
    	Employee emp = empManager.create();
    	
    	System.out.println(emp);
    }
}

Output:

EmployeeManagerImpl Bean is Created !!
Bean Factory Initialized !!
Employee [id=1, name=Lokesh]

Here, first bean has been created and initialized before the bean factory got fully initialized.

3.2. “With Lazy loading” enabled

Bean Factory Initialized !!
EmployeeManagerImpl Bean is Created !!
Employee [id=1, name=Lokesh]

After enable bean lazy loading, bean factory first for fully initialized. Later when we requested the EmployeeManager bean, factory then created the instance and returned it.

Drop me your questions in comments section related to difference between lazy loading and eager loading in Spring.

Happy Learning !!

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Feedback, Discussion and Comments

  1. how can we make dispatcher servlet as lazy loading in spring mvc

    Reply

  2. oh god.. spring 5 and configuration in XML, wtf dude

    Reply

    • Post has both versions of config. You can ignore the XML config and that’s perfectly normal. Trust me.

      Reply

  3. Hello Lokesh,

    I wanted to tell you that you made a typo in your titles, you should invert the titles because it is confusing:

    Instead of that:

    a) “With Lazy loading” enabled

    b) “Without Lazy loading” enabled

    Copy paste that:

    a) “Without Lazy loading” enabled

    b) “With Lazy loading” enabled

    Best regards,

    Pietr

    Reply

    • Thanks for taking time to report this. Much appropriated. Thank you !!

      Reply

  4. Hi Lokesh,
    Suppose if I pass wrong properties to a bean,

    <bean id="xyz" class="abc" lazy-init="true">
     <property name="nonexistent" value="random"/> <!-- class abc has no nonexistent property -->
</bean>

    And then don’t refer to this bean in the java code, why do I get error? If it was lazy initiated shouldn’t Spring IoC not bother about xyz bean while initializing ApplicationContext? And I should get error only when I try creating an object of abc class.

    Reply

    • There will not be any error if this bean “xyz” is not passed as dependency into any other eager-initialized bean. In such case, to validate/initialize the eager-initialized bean, spring will initialize this lazy init bean as well.

      If “xyz” bean is not used as dependency anywhere, then there will not be any error.

      Reply

      • hello Lokesh Sir

        I am little bit confuse to take applicationCcontext Ioc container that suppose i have mark lazy-init true in any bean(bean name abc) and other bean are mark false and if i request to get abc bean from applicationContext Ioc container then it will be initialized at a time of container load or when we request for that bean then it will be load.please put your comment.

        Thanks

        Reply

        • It will be initialized on demand. Not in container initialization.

          Reply

  5. Hi Lokesh,

    I am getting little confused after reading the first line of this blog which states that — “By default, Spring bean factory eagerly creates and initializes all ‘singleton scoped‘ beans during application startup itself.”

    Consider below code, After execution of this code I am getting below output in console logs:

    public class DrawingApp {
    public static void main( String[] args ) {
        System.out.println( "Hello World!" );
        BeanFactory  factory = new XmlBeanFactory(new FileSystemResource("spring.xml"));
		//<bean id="dummyObject" class="com.test.TestApplication" /> -- This is the only definition in spring.xml
        
	TestApplication testObject = (TestApplication) factory.getBean("dummyObject");	
        System.out.println("TestApplication Object hashCode :::: "+ testObject.hashCode());  
    }  
}

    Output:—–
    Hello World!
    Mar 02, 2018 11:21:20 AM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
    INFO: Loading XML bean definitions from file [D:\TUTORIAL\springcoretutorial\spring.xml]
    TestApplication Object hashCode :::: 12122356

    My question/confusion point is, after printing “Hello World!”, when getBean() method is called then it goes to load bean definition and then it provides result (which is lazy initialization). I don’t know my understanding is correct or not. Please put your comments.

    Thanks

    Reply

    • You have too sharp eyes. Thanks for catching it. Fact is that “BeanFactory uses lazy initialization approach whereas ApplicationContext uses eager initialization approach” i.e BeanFactory creates a singleton bean only when it is requested from it but ApplicationContext creates all singleton beans at the time of its own initialization.

      Reply

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