Dependency injection: Scoping by region (Guice, Spring, Whatever)

Posted by Itay on Stack Overflow See other posts from Stack Overflow or by Itay
Published on 2010-06-10T12:06:29Z Indexed on 2010/06/10 12:12 UTC
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Here's a simplified version of my needs.

I have a program where every B object has its own C and D object, injected through Guice. In addition an A object is injected into every C and D objects.

What I want: that for each B object, its C and D objects will be injected with the same A object.

Specifically, I want the output of the program (below) to be:

Created C0 with [A0]
Created D0 with [A0]
Created B0 with [C0, D0]
Created C1 with [A1]
Created D1 with [A1]
Created B1 with [C1, D1]

Where it currently produces the following output:

Created C0 with [A0]
Created D0 with [A1]  <-- Should be A0
Created B0 with [C0, D0]
Created C1 with [A2]  <-- Should be A1
Created D1 with [A3]  <-- Should be A1
Created B1 with [C1, D1]

I am expecting DI containers to allow this kind of customization but so far I had no luck in finding a solution. Below is my Guice-based code, but a Spring-based (or other DI containers-based) solution is welcome.

  import java.util.Arrays;
  import com.google.inject.*;

  public class Main {

    public static class Super {
      private static Map<Class<?>,Integer> map = new HashMap<Class<?>,Integer>();

      private Integer value;

      public Super(Object... args) {
        value = map.get(getClass());
        value = value == null ? 0 : ++value;
        map.put(getClass(), value);

        if(args.length > 0)
          System.out.println("Created " + this + " with " + Arrays.toString(args));
      }

      @Override
      public final String toString() {
        return "" + getClass().getSimpleName().charAt(0) + value;
      }
    }

    public interface A { }  
    public static class AImpl extends Super implements A  { } 

    public interface B { }  
    public static class BImpl extends Super implements B {
      @Inject public BImpl(C c, D d) { super(c,d); }
    }

    public interface C { }  
    public static class CImpl extends Super implements C  {
      @Inject public CImpl(A a) { super(a); }
    }

    public interface D { }  
    public static class DImpl extends Super implements D {
      @Inject public DImpl(A a) { super(a); }
    }


    public static class MyModule extends AbstractModule {
      @Override
      protected void configure() {
        bind(A.class).to(AImpl.class);
        bind(B.class).to(BImpl.class);      
        bind(C.class).to(CImpl.class);      
        bind(D.class).to(DImpl.class);      
      }    
    }

    public static void main(String[] args) {
      Injector inj = Guice.createInjector(new MyModule());
      inj.getInstance(B.class);    
      inj.getInstance(B.class);    
    }  
  }

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