依赖注入:按区域划分范围(Guice,Spring,Whatever)

Question

这是我需求的简化版本.

我有一个程序,其中每个B对象都有自己的C和D对象,通过Guice注入.此外,A对象被注入每个C和D对象.

我想要的是:对于每个B对象,它的C和D对象将被注入相同的A对象.

[编辑-开始]

(1)Guice支持"单例"和"原型"模式.但是,我需要的是介于两者之间的东西:我需要A对给定的B对象进行单例WRT(这样注入B对象的C和D将共享一个A对象).对于另一个B对象,我想要另一个A.所以它是一个单例,但对于程序的有限范围(实际上,数据结构的范围有限).

(2)我不介意使用方法(setter)或现场注入的解决方案.

(3)我曾多次尝试实现这一目标,并且总觉得我只需要实现DI容器的一些自定义东西来实现这一点 - 但它从未奏效.因此,我正在寻找一个详细的解决方案(而不仅仅是"挥手")

[编辑-完]

具体来说,我希望程序的输出(如下)为:

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]

它当前产生以下输出的位置:

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]

我期待DI容器允许这种定制,但到目前为止我没有找到解决方案的运气.下面是我的基于Guice的代码,但欢迎使用基于Spring(或其他基于DI容器)的解决方案.

  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);    
    }  
  }

Answer 1

这是基于原始代码的一种解决方案 - 有三种变化:

1. 将A,C和D的绑定移动到单独的子模块中
2. 将A标记为子模块中的单例
3. 在主模块中使用@Provides方法
   为每个请求提供BImpl实例和一个新的子注入器 - 这是子模块进入的位置

这是有效的,因为A的单例绑定现在仅限于每个子注入器.

[注意:
如果您不想继续为B的每个请求创建子模块实例,您可以将子模块实例缓存在主模块的字段中]

  import java.util.*;
  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() {} 

  // >>>>>>>>
      @Provides
      B builder( Injector injector ) {
        return injector.createChildInjector( new SubModule() ).getInstance( BImpl.class );
      }
  // <<<<<<<<
    }

  // >>>>>>>>
    public static class SubModule extends AbstractModule {
      @Override
      protected void configure() {
        bind(A.class).to(AImpl.class).in( Scopes.SINGLETON );
        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);    
    }  
  }