Guillaume Guillaume - 3 months ago 8
Java Question

Autowiring a collection via the constructor with Spring

I have what seems to be a simple problem, as stated in the title. Here is the kind of class I have :

public class Foo {
@Autowired
public Foo(@Qualifier("bar") Set<String> bar) {
// ...
}
}


Which I try to run with the following spring context :

<context:annotation-config />
<util:set id="bar">
<value>tata</value>
<value>titi</value>
<value>toto</value>
</util:set>
<bean id="foo" class="Foo" />


This fails to run with :


No matching bean of type
[java.lang.String] found for
dependency [collection of
java.lang.String]: expected at least 1
bean which qualifies as autowire
candidate for this dependency.
Dependency annotations:
{@org.springframework.beans.factory.annotation.Qualifier(value=bar)}


Note that if I add other parameters to my constructor, it works fine. If I use setter injection, it works fine. I'm sure I miss something obvious ... do you know what ?

Answer

Autowiring collections is not possible using the @Autowired annotation. An autowired collection means "to provide all beans of a particular type". Using the JSR-250 @Resource annotation, you can declare that you want a resource injected by its name, not its type. Or you inject the dependency explicitly.

[...] beans which are themselves defined as a collection or map type cannot be injected via @Autowired since type matching is not properly applicable to them. Use @Resource for such beans, referring to the specific collection/map bean by unique name.

See the Spring documentation for more details.

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