Spring @Configuration and Injecting Bean Dependencies as Method Parameters
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Join For FreeOne 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); } }
Published at DZone with permission of Biju Kunjummen, DZone MVB. See the original article here.
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