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Spring Framework - @Lazy Examples

Spring Framework 


@Lazy can be used on class or method or field level. It indicates whether a bean is to be initialized lazily. If this annotation is not present on a @Component or @Bean definition, eager initialization will occur.

In addition to using it with @Bean and @Component, this annotation may also be placed on injection points marked with @Autowired or @Inject or @Resource. In that case, the target variable will only be initialize with it's value when used first time.


@Lazy
@Service("basic-service")
public class ServiceImplA implements MyService {

    @PostConstruct
    private void init() {
        System.out.println("initializing lazily " +
                this.getClass().getSimpleName());
    }

    @Override
    public String getMessage() {
        return "Message from " + getClass().getSimpleName();
    }
}
Original Post




@Configuration
public class AppConfig {

    @Bean
    public AlwaysBeingUsedBean alwaysBeingUsedBean() {
        return new AlwaysBeingUsedBean();
    }

    @Bean
    @Lazy
    public RarelyUsedBean rarelyUsedBean() {
        return new RarelyUsedBean();
    }

    public static void main(String... strings) {
        AnnotationConfigApplicationContext context =
                new AnnotationConfigApplicationContext(AppConfig.class);
        System.out.println("Spring container started and is ready");
        RarelyUsedBean bean = context.getBean(RarelyUsedBean.class);
        bean.doSomething();
    }
}
Original Post




This example demonstrates the use of @Lazy at the injection point. 

package com.logicbig.example;

import jakarta.annotation.PostConstruct;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Lazy;

public class MyEagerBean {

    @Autowired
    @Lazy
    private MyLazyBean myLazyBean;

    @PostConstruct
    public void init() {
        System.out.println(getClass().getSimpleName() + " has been initialized");
    }

    public void doSomethingWithLazyBean() {
        System.out.println("Using lazy bean");
        myLazyBean.doSomething();
    }
}
package com.logicbig.example;

import jakarta.annotation.PostConstruct;

public class MyLazyBean {

    @PostConstruct
    public void init () {
        System.out.println(getClass().getSimpleName() + " has been initialized");
    }

    public void doSomething () {
        System.out.println("inside lazy bean doSomething()");
    }
}

package com.logicbig.example;

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

public class LazyExampleMain {

    public static void main (String[] args) {
        ApplicationContext context =
                  new AnnotationConfigApplicationContext(
                            MyConfig.class);
        System.out.println("--- container initialized ---");
        MyEagerBean bean = context.getBean(MyEagerBean.class);
        System.out.println("MyEagerBean retrieved from bean factory");
        bean.doSomethingWithLazyBean();
    }

    public static class MyConfig {

        @Bean
        public MyEagerBean eagerBean () {
            return new MyEagerBean();
        }

        @Bean
        @Lazy
        public MyLazyBean lazyBean () {
            return new MyLazyBean();
        }
    }
}

Output

MyEagerBean has been initialized
--- container initialized ---
MyEagerBean retrieved from bean factory
Using lazy bean
MyLazyBean has been initialized
inside lazy bean doSomething()
Original Post

See Also