java - 具有循环依赖的 HK2 注入(inject)

Question

我使用 HK2 作为依赖注入(inject)框架。我正在我的应用程序中实例化一个状态机。因此，A <-> B 是很有可能的，因为根据输入，可以从 B 转换回 A。

@Singleton 
class StateManager extends SomeInterface{

    @Inject
    private B b;

    @Inject
    private A a;
}

@Singleton 
class A extends State{

    @Inject
    private B b;

    @Inject
    private StateManager sm;

}

@Singleton 
class B extends State{

    @Inject
    private A a;

    @Inject
    private StateManager sm;
}

我怎样才能实现这样的目标？上面的例子只是为了说明。我有比这更多的状态。我试图查看它是否重复，但找​​不到可以处理的。当我尝试 ServiceLocator.getService(StateManager.class) 获取此图时，出现循环依赖异常。做这样的事情有什么好处？

Answer 1

您应该能够注入(inject) javax.inject.Provider<B> .来自 Javadoc

Provides instances of T. Typically implemented by an injector. For any type T that can be injected, you can also inject Provider<T>. Compared to injecting T directly, injecting Provider<T> enables:

• retrieving multiple instances.
• lazy or optional retrieval of an instance.
• breaking circular dependencies.
• abstracting scope so you can look up an instance in a smaller scope from an instance in a containing scope.

然后调用get()当你需要的时候

B b = bProvider.get();