Spring autowire and prototype scope

Question

I have a class named Bar with the following annotation: @Configurable(autowire = Autowire.BY_TYPE)

On a private member I have the following annotation:

@Autowired(required = true)
private Foo foo;

In the spring configuration I have a bean of class Foo. If the bean is defined with scope="prototype" it doesn't work and I get the following exception:

NoSuchBeanDefinitionException: No matching bean of type Foo found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency

Once I change the injected bean scope to "singleton" it works fine.

Isn't auto wiring of prototype scoped bean allowed?

Is there any workaround (beside getting the bean manually)?

Thanks in advance, Avner

Answer 1

If the injected bean scope is 'Singleton', the same instance of the bean will be auto-wired. If the injected bean scope is 'prototype', new instance will be created as part of auto-wire process.

What version of Spring you are using and also attach the spring-context.xml for more details.

Answer 2

I believe its the prototype/singleton thing declared in your xml for that bean is the issue.

Isn't auto wiring of prototype scoped bean allowed?

I think it is not allowed. The logic is if it is allowed, then whenever you use that class, then it needs to reinstantiate that bean always as its field. Which is weird especially if the class that this bean is autowired as a field is a singleton itself.

is there any workaround (beside getting the bean manually)?

Just try to remove the scope attribute, cause if it is of prototype attribute, it won't be retrieved. If those beans(services and DAO) are declared in your applicationContext, just let the autowire annotation get it as singleton since by default beans are singleton, which it should be.

Answer 3

The following links provide alternative solutions for such scenarios:

1. http://whyjava.wordpress.com/2010/10/30/spring-scoped-proxy-beans-an-alternative-to-method-injection/
2. http://benkiew.wordpress.com/2012/04/22/spring-2-5-x-create-prototype-instances-from-code/

The first link talks about adding to Foo:

@Component
@Scope(proxyMode = ScopedProxyMode.TARGET_CLASS, value = "prototype")
class Foo

Which will cause a new instance every call.