Spring bean lazy initialization

Question

I was thinking about the lazy-initialization of beans in Spring. For me, it wasn't crystal clear that the "lazy" here means that a bean will be created when it's referenced.

I expected that the lazy initialization support in Spring is different. I thought this is a "method-call" based lazy creation. What I mean by this is, whenever any method is being called on the method, it will be created.

I think this could be easily solved by creating a proxy instance of the specific bean and do the initialization on any method call.

Am I missing something why this is not implemented? Is there any problem with this concept?

Any feedback/idea/answer will be appreciated.

Savior · Answer 1 · 2016-04-24T01:35:16.487

You can achieve the behavior you want by scoping your bean with a proxyMode of ScopedProxyMode.TARGET_CLASS (CGLIB) or ScopedProxyMode.INTERFACES (JDK).

For example

public class StackOverflow {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext(Conf.class);
        Bar bar = ctx.getBean(Bar.class);
        System.out.println(bar);
        System.out.println(bar.foo.toString());
    }
}

@Configuration
class Conf {
    @Bean
    @Lazy
    @Scope(proxyMode = ScopedProxyMode.TARGET_CLASS)
    public Foo foo() {
        System.out.println("heyy");
        return new Foo();
    }

    @Bean
    public Bar bar() {
        return new Bar();
    }
}

class Bar {
    @Autowired
    public Foo foo;
}

class Foo {
}

will print

com.example.Bar@3a52dba3
heyy
com.example.Foo@7bedc48a

demonstrating that the Foo bean was initialized through its @Bean factory method only after a method was invoked on the Foo instance injected by the Spring context in the Bar bean.

The @Scope annotation can be used in a class declaration as well.

Do you know how to make lazy-load of beans like this? "return FactoryProvider().getFactory()" — Fisk, Feb 15 '17 at 11:40

score -1 · Answer 2 · answered Apr 24 '16 at 04:15

bellow is my views:

Bean types in Spring Container:

There are two Scope bean type in Spring Container.One is Prototype, this type bean won't exist lazy-init concept, because these beans will be instantiated when clients invoke the getBean() method every time. Another is Singleton, these bean will be instantiated once, these beans can be lazily instantiated(just be instantiated when they're used, such as @Autowired, refrenced) if you define the bean use @Lazy or lazy-init=true.

How to implement lazy-init:

Yes, common implementation is Proxy Mode. Spring use JDK Dynamic Proxy and Cglib to implement Proxy, you can go further understanding about these techs.

Hope to help you.

Spring bean lazy initialization

2 Answers2