Does calling @Bean methods create a new instance of the object or the bean instance?

Question

In the code below, is calling bar() inside foo.setBar(bar()) and blah.setBar(bar()) using two difference instances of Bar? Or is it using a bean instance of Bar instead? If it's a bean instance, how does Spring do it automagically? Is it achieved by proxy?

@Configuration
public class AppConfig {
    @Bean
    public Foo foo() {
        Foo foo = new Foo();
        foo.setBar(bar());
        return foo;
    }

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

    @Bean
    public Blah blah() {
        Blah blah = new Blah();
        blah.setBar(bar());
        return blah;
    }
}

score 7 · Accepted Answer · answered Mar 18 '16 at 07:18

Spring creates a proxy of your @Configuration annotated classes. This proxy intercepts @Bean method calls and caches the bean instances so that further calls to the same @Bean method refers to the same bean instance.

Hence in your case both calls to bar() method refers to the same Bar instance.The Bar instance is actually a singleton per application context.This is why the @Bean methods visibility is restricted to either protected , package or public because Spring needs to override your @Bean methods in the proxy.

score 1 · Answer 2 · edited May 23 '17 at 11:50

1

Single bean instance will be used and it is achieved using proxies. Spring uses the concept of Inheritance based proxies to achieve this. Please take a look at - How to exactly work the Spring Inheritance-based Proxies configuration?

edited May 23 '17 at 11:50

Community

1
1

answered Mar 18 '16 at 10:11

asg

2,248
3
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score 0 · Answer 3 · answered Mar 18 '16 at 07:17

0

the same bean instance will be used in your case because a singleton scope is used by default for '@Bean' annotation.

yes, it's achived by spring proxying internals.

answered Mar 18 '16 at 07:17

ivanenok

594
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9

Does calling @Bean methods create a new instance of the object or the bean instance?

3 Answers3