JavaGuice：在创建模块之前实例化一个单例

Question

在创建模块之前，是否可以用Guice实例化一个引用并将其分配给该引用，并在配置期间将该实例传递给要绑定的模块构造函数

以下是我的意思的一个例子： 我有一个方法，允许我根据接口的自定义实现创建对象，该接口作为可选的（如果用户不提供自定义实现，我们将使用默认实现）在构造函数中传递，这是通过将接口绑定到模块类中的特定实现来完成的

public static MyClass createMyClassObject(Optional<SpecialInterface> customSpecialInterfaceObject) {

    SpecialInterface specialInterfacebject;

    if(customSpecialInterfaceObject.isPresent() {    
        specialInterfaceObject = customSpecialInterfaceObject.get()
    } else {
 /* here I would like to bind it to an instance of the DefaultSpecialInterfaceObject but can't really do something like:
Injector injector = Guice.createInjector(myClassModule);
DefaultSpecialInterface instance = injector.getInstance(DefaultSpecialInterface.class);
as the module is yet to be created */
}
    MyClassModule myClassModule = new MyClassModule(specialInterfaceObject);
    Injector injector = Guice.createInjector(myClassModule);
     return injector.getInstance(MyClass.class);
}

我目前使用类而不是实例来解决这个问题，比如下面的例子，但我不太喜欢这个解决方案。我很乐意看到更好的方法：

private static Class resolveSpecialInterfaceObject(Optional<SpecialInterface> customSpecialInterfaceObject) {
    Class specialInterfaceObjectClass;

    if (customSpecialInterfaceObject.isPresent()) {
        specialInterfaceObjectClass= customSpecialInterfaceObject.get().getClass();
    } else {
        specialInterfaceObjectClass = DefaultSpecialInterface.class;
    }
    return specialInterfaceObjectClass;
}

public abstract class MyClassModule extends AbstractModule {

    private final Class<SpecialInterface> specialInterfaceObjectClass;

    public MyClassModule(Class<SpecialInterface> specialInterfaceObjectClass) {
    this.specialInterfaceObjectClass= specialIntefaceObjectClass;
    }

    @Override
    protected void configure() {
        bind(SpecialInterface.class).to(specialInterfaceObjectClass);
        }
}

编辑以下评论：

one more thing- didn't want to make the question too long; actually, I also want to perform another operation on the resulting instance of SpecialInterface, but only if it is the instance of DefaultSpecialInterface and I don't think it should be done in the Module. I was thinking if I could just have this bean up and running before, such as in Spring, so I could just pass it to the Module, but also use it in another method call before?

Answer 1

你能把整个Optional用bind(...).toInstance(...)吗

public static MyClass createMyClassObject(
        Optional<SpecialInterface> customSpecialInterfaceObject) {

    MyClassModule myClassModule = new MyClassModule(customSpecialInterfaceObject);
    Injector injector = Guice.createInjector(myClassModule);
    MyClassFactory instance = injector.getInstance(MyClassFactory.class);
    return instance.createMyClassObject();
}

class MyClassModule extends AbstractModule {
  private final Optional<SpecialInterface> customObject;

  MyClassModule(Optional<SpecialInterface> customObject) {
    this.customObject = customObject;
  }

  @Override public void configure() {
    if (customObject.isPresent()) {
      // Singleton by necessity: Guice doesn't know how to create another one.
      bind(SpecialInterface.class).toInstance(customObject.get());
    } else {
      // Default scoped. Add ".in(Singleton.class)" if necessary.
      bind(SpecialInterface.class).toInstance(DefaultSpecialInterfaceClass.class);
    }
  }
}

如果只想在DefaultSpecialInterface上执行其他初始化操作，则有许多选项：

• 如果某种初始化对所有实现都很重要，并且可能太重而无法放入类构造函数中，那么在SpecialLinterface上添加initialize方法。将自定义设置为no-op，并为DefaultSpecialLinterface实现它

• 如果初始化是DefaultSpecialInterface独有的，那么我看不出它不应该出现在模块中的原因。编写@Provides方法或绑定到Provider<SpecialInterface>以正确创建和初始化DefaultSpecialInterface

• 如果您的真正目标是将业务逻辑排除在模块之外，那么可以通过将其提取到一个独立的提供者或DefaultSpecialInterfaceFactory中来实现，该提供者或DefaultSpecialInterfaceFactory负责

请记住，Guice负责将完全构造的对象输入到对象图中，这意味着注入SpecialInterface应该让SpecialInterface通用契约的实现者随时可用。如果Guice需要执行一些初始化来实现这一点，那么让它这样做并不是不合理的，模块也不是一个不好的地方