Why is #Autowired working differently in application and test? - spring

Question

I made a sample program revealing my question:
package test;
public interface InterfaceA {
}
package test;
public class ClassA implements InterfaceA {
}
package test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
#Configuration
public class Application {
#Bean
public InterfaceA beanA() {
return new ClassA();
}
#Autowired
private ClassA beanA;
public static void main(String[] args) {
AnnotationConfigApplicationContext applicationContext
= new AnnotationConfigApplicationContext(Application.class);
}
}
#Autowired doesn't work with the concrete class in this application code.
package test;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.test.context.ContextConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration(classes = Application.class)
public class ApplicationTest {
#Autowired
ClassA beanA;
#Test
public void di() {
System.out.println(beanA);
}
}
But #Autowired works with the concrete class in this test code.
Why is #Autowired working differently in application and test?
I shared the above code at:
https://github.com/izeye/SpringTest

Answer 1

You're using your application context in the main entry point of the application. Make an additional 'Main' class and wire in your context like so:
#Autowired
Application context;
In your test, you're taking the time to start up the application context when you use the annotation: #ContextConfiguration(classes = Application.class).
In your concrete example you're referencing the context in the same class that you're trying to use it in. When you initialize the context in the main, the instance of Application that is running the code has already been instantiated, and did not get autowired, because at the time of its instantiation there wasn't any context for it to use.

Answer 2

It is a bit tricky:
Solution would be to make beanA static method and annotate Application with #Lazy or #DependsOn(value="beanA") annotations. I.e. something like this:
#Configuration
#Lazy
public class Application {
#Bean
public static InterfaceA beanA() {
return new ClassA();
}
#Autowired
private ClassA beanA;
public static void main(String[] args) {
AnnotationConfigApplicationContext applicationContext
= new AnnotationConfigApplicationContext(Application.class);
}
}
Reason: for actual beanA bean creation spring need to instantiate Application class first. And while trying to resolve reference to a beanA the only information container has about this future bean is its type (InterfaceA) since there is no actual implementation exists.
However in a case of test class context was already initialized and bean can be resolved by actual implementation class which physically was already created. Same would be if you will try to reference beanA by class from any other spring component.