在@Configuration中提供对spring @Bean的依赖关系的正确方法

Question

In @Configuration class it is possible to create spring bean by using method with @Bean annotation

@Component
public class Foo {
}

public class Bar {
  private Foo foo;

  public Bar(Foo foo) {
    this.foo = foo;
  }
}

@Configuration
public class BarConfig {
  @Bean
  public Bar bar(Foo foo) {
    return new Bar(foo);
  }
}

But injecting Foo to BarConfig class and using it that way can let you create Bar as well:

@Component
public class Foo {
}

public class Bar {
  private Foo foo;

  public Bar(Foo foo) {
    this.foo = foo;
  }
}

@Configuration
public class BarConfig {
  @Autowired
  private Foo foo;

  @Bean
  public Bar bar() {
    return new Bar(foo); // bar() without args
  }
}

Is there any difference, from spring perspective, between them? Is 2nd incorrect? What would it break or what would not work because of it?

I managed to find that with 2nd there is no visible dependency to foo from Bar but would it affect anything? Refreshing/reloading spring context would pick up the change in foo while remaking bar, wouldn't it?

Answer 1

The only difference between this two types of autowiring is amount of code that has to be written.

I recommend you to use the first option simply because it is shorter.

The second option is suitable in case if you have to specify @Qualifier annotation in pair with @Autowired and the been which you want to inject declared in separate configuration.