How to use Spring Autowired (or manually wired) in Scala object?

Question

I am trying to use Spring with Scala. I know Autowired works with Scala class, but I am using a web-framework that requires an object and I want to inject a dao into it. I w

Answer 1

All that's actually necessary is that you define your object as a class, rather than an object. That way Spring will instantiate it.

 @Service
    object UserRest extends RestHelper {
        @Autowired
        @BeanProperty
        val userRepository: UserRepository = null;

        .....
    }
<beans>
         .....
         <bean id="userRest" class="com.abc.rest.UserRest" >
              <!--- this is my attempt to manually wire it --->
              <property name="userRepository" ref="userRepository"/>
         </bean>
    </beans>

Changing the "val" to "var" is unnecessary (Spring uses reflection, which ignores immutability). I'm pretty sure that that @BeanProperty is also unnecessary (Spring will assign to the underlying field, reflectively).

Answer 2

Basically, you have two problems:

• Property should be mutable, i.e. var rather than val

• All methods of Scala object are static, whereas Spring expects instance methods. Actually Scala creates a class with instance methods named UserRest$ behind the scene, and you need to make its singleton instance UserRest$.MODULE$ available to Spring.
  Spring can apply configuration to preexisting singleton instances, but they should be returned by a method, whereas UserRest$.MODULE$ is a field. Thus, you need to create a method to return it.

So, something like this should work:

object UserRest extends RestHelper {
   @BeanProperty
   var userRepository: UserRepository = null;

   def getInstance() = this
   ...
}

.

<bean id="userRest" 
    class="com.abc.rest.UserRest" 
    factory-method = "getInstance">
    <property name="userRepository" ref="userRepository"/>
</bean>

You can replace <property> with @Autowired, but cannot replace manual bean declaration with @Service due to problems with singleton instance described above.

See also:

• What is the Java equivalent of a Scala object?
• 3.3.2.2 Instantiation with a static factory method