In Spring, what does 'autowire = Autowire.NO' do?

configuration, spring

Solution

Setting `Autowire.NO` does not mean that the bean cannot be injected in other beans via `@Autowire`. `@Autowire` works by default by type, and can also work by name using `@Qualifier`.

So if your bean has the right type or name, it will get inject in other beans, that's normal.

`Autowire.NO` means something like:

Don't inject the properties of THIS bean being declared with `@Bean` neither by type or by name. If the bean properties are not set in the `@Bean` method code, leave them unfilled.

This a code example of how this works, let's define two beans:

public class MyBeanTwo {

    public MyBeanTwo() {
        System.out.println(">>> MY Bean 2 created!");
    }
}

public class MyBean {

    private MyBeanTwo myBeanTwo;

    public MyBean() {
        System.out.println(">>>MyBean created !!");
    }

    public void setMyBeanTwo(MyBeanTwo myBeanTwo) {
        System.out.println(">>> Injecting MyBeanTwo INTO MyBeanOne !!!");
        this.myBeanTwo = myBeanTwo;
    }
}

And some configuration:

@Configuration
public class SimpleConfigOne {

    @Bean
    public MyBean createMyBean()   {
        return new MyBean();
    }

    @Bean
    public MyBeanTwo createMyBeanTwo() {
        return new MyBeanTwo();
    }
}

With this configuration, the startup of this application gives this log:

>>>MyBean created !!
>>> MY Bean 2 created!

Meaning one instance of each bean was created, but `MyBean` did NOT get injected with `MyBeanTwo`, even tough a bean with the correct type existed.

By declaring `MyBean` like this:

@Bean(autowire = Autowire.BY_TYPE)
public MyBean createMyBean()   {
    return new MyBean();
}

`MyBeanOne` is now eligible to have it's properties set via autowiring by type.

The startup log becomes:

>>>MyBean created !!
>>> MY Bean 2 created!
>>> Injecting MyBeanTwo INTO MyBeanOne !!!

This shows that `MyBean` had `MyBeanTwo` injected by type via a by type injection.

Reason why Autowire.NO is the default:

Usually we don't want to autowire the properties of beans created with `@Bean`. What we usually do is set the properties explicitly via code for readability, as a form of documentation and to make sure the property is set with the correct value.

Problem

From this Spring documentation I know that when I use @Bean, the default is already equivalent to: @Bean(autowire = Autowire.NO) (Default) No autowiring. Bean references must be defined via a ref element. Changing the default setting is not recommended for larger deployments, because specifying collaborators explicitly gives greater control and clarity. To some extent, it documents the structure of a system. I am just trying to understand what this means for me. If my system is 100% Java Config and has no XML configuration, then from what I can tell, when I use @Bean, the 'Autowire.no' has no impact whatsoever. EDIT By "no impact" I mean that other @Autowired references to this bean ARE autowired (in other Java Config classes). I suspect that is because with Java Config there is no explicit 'ref element' defined, so this (default) setting has no effect. Example: First Config: ``` package a.b.c; @Configuration public class AlphaConfig { @Bean(autowire = Autowire.NO) public AlphaBeanType alphaBean() { return new AlphaBeanType(); } } ``` Then in second config: ``` package d.e.f; import a.b.c.AlphaBeanType; @Configuration public class AnotherConfig { @Autowire private AlphaBeanType alphaBeanType; @Bean . . . } ``` What I see is that 'alphaBeanType' is always autowired in the second config class - which seems to be in conflict with the documentation - hence my question. end edit Of course, I can't quite tell from the documentation! Does anyone know for sure?

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