Question

I like constructor-based injection as it allows me to make injected fields final. I also like annotation driven injection as it simplifies my context.xml. I can mark my constructor with @Autowired and everything works fine, as long as I don’t have two parameters of the same type. For example, I have a class:

@Component
public class SomeClass {
    @Autowired(required=true)
    public SomeClass(OtherClass bean1, OtherClass bean2) {
        …
    }
}

and an application context with:

<bean id="bean1" class="OtherClass" />
<bean id="bean2" class="OtherClass" />

There should be a way to specify the bean ID on the constructor of the class SomeClass, but I can’t find it in the documentation. Is it possible, or am I dreaming of a solution that does not exist yet?

Answer 1

@Autowired is by-type (in this case); use @Qualifier to autowire by-name, following the example from spring docs:

public SomeClass(
    @Qualifier("bean1") OtherClass bean1, 
    @Qualifier("bean2") OtherClass bean2) {
    ...
}

Note: In contrast to @Autowired which is applicable to fields, constructors and multi-argument methods (allowing for narrowing through qualifier annotations at the parameter level), @Resource is only supported for fields and bean property setter methods with a single argument. As a consequence, stick with qualifiers if your injection target is a constructor or a multi-argument method.

(below that text is the full example)