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Spring @Configuration and injecting bean dependencies as method parameters

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One of the ways Spring recommends injecting inter-dependencies between beans is shown in the following sample copied from the Spring's reference guide here:

@Configuration
public class AppConfig {

@Bean
public Foo foo() {
return new Foo(bar());
}

@Bean
public Bar bar() {
return new Bar("bar1");
}

}
So here, bean `foo` is being injected with a `bar` dependency.

However, there is one alternate way to inject dependency that is not documented well, it is to just take the dependency as a `@Bean` method parameter this way:

@Configuration
public class AppConfig {

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

@Bean
public Bar bar() {
return new Bar("bar1");
}

}

There is a catch here though, the injection is now by type, the `bar` dependency would be resolved by type first and if duplicates are found, then by name:

@Configuration
public static class AppConfig {

@Bean
public Foo foo(Bar bar1) {
return new Foo(bar1);
}

@Bean
public Bar bar1() {
return new Bar("bar1");
}

@Bean
public Bar bar2() {
return new Bar("bar2");
}
}

In the above sample dependency `bar1` will be correctly injected. If you want to be more explicit about it, an @Qualifer annotation can be added in:

@Configuration
public class AppConfig {

@Bean
public Foo foo(@Qualifier("bar1") Bar bar1) {
return new Foo(bar1);
}

@Bean
public Bar bar1() {
return new Bar("bar1");
}

@Bean
public Bar bar2() {
return new Bar("bar2");
}
}


So now the question of whether this is recommended at all, I would say yes for certain cases. For eg, had the bar bean been defined in a different @Configuration class , the way to inject the dependency then is along these lines:

@Configuration
public class AppConfig {

@Autowired
@Qualifier("bar1")
private Bar bar1;

@Bean
public Foo foo() {
return new Foo(bar1);
}

}

I find the method parameter approach simpler here:

@Configuration
public class AppConfig {

@Bean
public Foo foo(@Qualifier("bar1") Bar bar1) {
return new Foo(bar1);
}

}


Thoughts?

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