Can Spring DI deduce depenendencies from code like Autofac, without annotations?

Question

Autofac is an Inversion of Control container for .net. It has this attractive (to me) feature:

When Autofac instantiates a component, it satisfies the component's dependencies by finding and instantiating other components.

Components express their dependencies to Autofac as constructor parameters:

public class TaskController : IController 
{
    public TaskController(ITaskRepository tasks) { ... }
}

In this case Autofac will look for another component that provides the ITaskRepository service and call the constructor of TaskController with that component as a parameter.

(source: http://code.google.com/p/autofac/)

For the simplest case where there's a single implementation for a given interface this works neatly - without requiring any meta-data about the dependency (attributes/XML/config class).

Does Java's "Spring DI" container support the same functionality?

Answer 1

I'm looking for the DI container to deduce this information from the bytecode rather than me having to supply it in XML.

I don't believe Spring has such functionality. If you could annotate your constructor like so

@Autowired
public TaskController(ITaskRepository tasks) { ... }

and there was only one bean that implements ITaskRepository in the context, then Spring could figure it out, but you'll need the annotation.

---

Correct me if I misunderstood your question.

If you don't have control of the class to add annotations, you can still use the <bean> <constructor-arg> element to reference and use another bean when invoking the constructor.

<bean id="taskRepository" class="com.some.TaskRepositoryImpl" />

<bean id="taskController" class="com.some.TaskController">
    <constructor-arg ref="taskRepository" />
</bean>

Alternatively, with Java configuration

@Bean
public ITaskRepository taskRepository() {
    return new TaskRepositoryImpl();
}

@Bean
public TaskController taskController() {
    return new TaskController(taskRepository());
}