Question

我正在使用Guice Assisted Inject库为我建造工厂。我目前的设置如下：

class MyObject {
  @Inject public MyObject(@Assisted FirstDep first, @Assisted SecondDep second, ThirdDep third) { /**/ }
}

class FirstDep { /* nothing to see here */ }
class SecondDep {
  @Inject public SecondDep(@Assisted FirstDep first) { /**/ }
}
class ThirdDep { /* nothing to see here either */ }

class MyModule extends AbstractModule {
  @Override public void configure() {
    bind(ThirdDep.class);
    install(new FactoryModuleBuilder().build(MyObjectFactory.class));
  }
}

interface MyObjectFactory {
  SecondDep createSecond(@Assisted FirstDep first);
  MyObject createMyObject(@Assisted FirstDep first, @Assisted SecondDep second);
}

这迫使我使用SecondDep明确创建factory.createController(first, factory.createSecond(first))。是否可以更改我的绑定，以便我可以简单地执行factory.createController(first)，它会自动使用SecondDep绑定和我传入的参数？

Answer 1

考虑您在此处创建的API，尤其是有关未来扩展或实现的API。你显然有很多有状态的FirstDep实例，因为SecondDep取决于特定的FirstDep，但未来的SecondDep可能不依赖于相同的FirstDep（或任何FirstDep）。 createMyObject(first)可以作为createMyObject(first, factory.createSecond(first))的简写这一事实特定于您的商业案例，而且我认为Guice中没有简写来做出这样的假设。

那就是说，你有两种选择。一，你可以创建一个非常小的帮手：

// Encapsulate the createMyObject(first) shorthand.
class MyObjectHelper {
  @Inject MyObjectFactory rawFactory;

  MyObject createMyObject(FirstDep first) {
    return rawFactory.createMyObject(first, rawFactory.createSecond(first));
  }
}

或者，两个，您可以使用@AssistedInject让Guice有效地重载构造函数：

class MyObject {
  // Multiple @AssistedInject constructors, selected based on which parameters
  // are marked with @Assisted.

  @AssistedInject public MyObject(@Assisted FirstDep first,
       SecondFactory secondFactory, ThirdDep third) {
    this(first, secondFactory.createSecond(first), third);
  }

  @AssistedInject public MyObject(@Assisted FirstDep first,
      @Assisted SecondDep second, ThirdDep third) { /**/ }
}

interface SecondFactory {
  // Note that @Assisted annotations are not needed here. Every parameter in
  // these interfaces is for assisted injection, by definition.
  SecondDep createSecond(FirstDep first);
}

interface MyObjectFactory {
  MyObject createMyObject(FirstDep first);
  MyObject createMyObject(FirstDep first, SecondDep second);
}

虽然每个类创建一个单独的工厂稍微冗长一些，但我认为您会发现它有助于保持您的课程/工厂分离且易于遵循，并且它巧妙地避免了潜在的循环引用如果Guice支持，我不记得了。我倾向于将我的工厂暴露为嵌套接口：

class SecondDep {
  interface Factory {
    SecondDep create(FirstDep first);
  }

  @Inject public SecondDep(@Assisted FirstDep first) { /**/ }
}

...然后，您可以找到并更新Second.Factory与其支持的类完全相邻。

链接使用guice辅助注射辅助注射参数

1 个答案: