java - 发现循环依赖问题

Question

我正在设计一个系统，其中有两个模块，一个用于管理文件，另一个用于用户。对于某些逻辑运算，它们需要彼此提供的服务。

每个模块都由一个单例表示，该单例实现一个相互提供一些服务的接口(interface)，并通过抽象工厂来提供它们，如下所示:

public class UserMain implements UserInternalService {

/*
 * Internal interfaces
 */
/**
 * Allows interaction with the projects database.
 */
FilesInternaService fileSystem;

/**
 * Constructor is private, as this is a singleton.
 */
protected UserMain() {
}

private static UserMain singleton = null;

/**
 * Singleton factory. Returns a reference to the singleton. If there is no
 * reference yet, creates it.
 */
protected static synchronized UserMain getReference() {
    if (singleton == null) {
        singleton = new UserMain();
        singleton.fileSystem = FileMain.getInternalService();
    }
    return singleton;
}

/**
 * Factory method for the singleton as a UserInternalService
 */
public static UserInternalService getUserInternalService() {
    return getReference();
}

}

文件模块主类如下:

public class FileMain implements FilesInternaService{

/**
 * Interface to user subsystem for request validation, etc.
 */
UserInternalService userSystem;

/**
 * Creation of instances aside from singleton disallowed.
 */
protected FileMain(){};

private static FileMain singleton = null;

/**
 * Singleton factory.
 * Returns a reference to the singleton.
 * If there is no reference yet, creates it.
 */
protected synchronized static FileMain getReference(){
    if(singleton == null)
        singleton = new FileMain();
        singleton.userSystem = UserMain.getUserInternalService();
    return singleton;
}

/**
 * Abstract factory for Internal Services singleton.
 * @return
 */
public static FilesInternaService getInternalService(){
    return getReference();
}
}

我不确定我是否正确处理了循环依赖。有什么办法可能会意外中断吗？

编辑:正如下面已经回答的那样，处理这个问题的正确方法是注入(inject)。然而，处理这个问题的正确方法不是我在这里问的，而是这个特定的解决方案如何崩溃。

Answer 1

处理此问题的简洁方法是使用依赖项注入(inject)，将依赖项保留在接口(interface)级别。

UserMain 可以依赖 FilesInternaService，FileMain 也可以依赖 UserInternalService；但 UserMain 不能依赖 FileMain 或 FileMain 依赖 UserMain。换句话说，依赖具体实现是不行的。

FilesInternaService 的实例应注入(inject)到 UserMain 中，UserInternalService 的实例应注入(inject)到 FileMain 中.

引用文献

1. Are circular dependencies considered bad design?
2. Why are circular references considered harmful?
3. https://softwareengineering.stackexchange.com/questions/11856/whats-wrong-with-circular-references
4. https://softwareengineering.stackexchange.com/questions/306483/how-to-solve-circular-dependency