Spring Documentation for Component Scan versus Configuration

Question

I've searched for an answer to this question but my search voodoo must be a little off.

At work I've noticed there's a preference to use Spring Configuration and @Beans to initialise our Java objects. While there is no problem with this approach I thought switching over to @Component (with ComponentScan) might

Slightly simplify the code
Put us more inline with good Spring practices

But, thinking about it, I'm having trouble justifying why I consider it a good practice. My understanding of @Bean is that it's useful for initialising legacy or non-Springified, code. That may be causing me to consider @Component as a good practice.

An advantage to the @Bean approach is that it centralises the initialisation. This is a little easier to understand in contrast to @Component which is not as immediately intuitive.

Does Spring have any good documentation on the pros and cons of each approach? Or a best practices guide for this topic?

Pospolita Nikita · Accepted Answer · 2018-06-25 16:39:42Z

1

@Configuration class with @Bean-s inside it is called "Java based configuration". And it's more flexible, then "Annotation based configuration" (@Component).

It is perfectly valid to have Java configuration and annotated component scans in the same project because they server different purposes.

@Component (@Service, @Repository etc) are used to auto-detect and auto-configure beans.

@Bean annotation is used to explicitly declare a single bean, instead of letting Spring do it automatically. You can provide more settings to bean instantiated that way.

You can do the following with @Bean. But, this is not possible with @Component:

@Bean
public MyService myService(boolean someCondition) {
    if(someCondition) {
      return new MyServiceImpl1();
    } else {
        return new MyServiceImpl2();
    }
}

answered Jun 25, 2018 at 16:39

Pospolita Nikita

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7 Comments

Shane Gannon Over a year ago

Does the Spring community have any preference? Realistically with Component a mixed approach will always be used. Is there any reason to ignore Component and simply stick with Bean?

Pospolita Nikita Over a year ago

I can say that usually both approaches are used in projects. It's not one vs. another. Sometimes you need to configure beans from third-party libs, in this case you need to provide configured bean to context via Java-based configuration.

Pospolita Nikita Over a year ago

Also, Java-based configurations are very handy in integration tests

Shane Gannon Over a year ago

That was one of the noted benefits of Beans. But I've noticed it's possible to define a Component as a Bean for testing and it works.

Darren Forsythe Over a year ago

Java based configuration is preferable for testing as you only import the configuration classes you require to test whatever slice of the application you want to. e.g. MyDatabaseConfigurion, MyServiceConfiguration. ComponentScanning rapidly gets messy as you do not have a central point of reference to where beans are defined, and if you only want to test a slice of your application you will likely end up loading more than needed. Configuration classes give a central point of access.

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