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 e.g, 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?
| Reference: | Spring @Configuration and injecting bean dependencies as method parameters from our JCG partner Biju Kunjummen at the all and sundry blog. |
