java - 从接口(interface)创建全局唯一对象

Question

这更多的是一个架构问题。我希望在我的项目中有一个全局对象，每个需要它的类都可以访问它，但不需要每次都创建它的实例。对象本身是不同服务的组合。我的第一种方法是定义一个接口(interface)，在该接口(interface)中实例化对象，然后只需说 implements 即可将其注入(inject)到每个类中。我想知道的是，这种方法是干净的还是有点hacky或者真的很恶心。这是我到目前为止的实现:

public final class SystemServices
{
    private final SecurityService securityService;
    private final PersistencyService persistencyService;
    private final RecordService recordService;
    private final DispatcherService dispatcherService;

    private SystemServices(Builder builder)
    {
        this.securityService = builder.securityService;
        this.persistencyService = builder.persistencyService;
        this.recordService = builder.recordService;
        this.dispatcherService = builder.dispatcherService;
    }

    public SecurityService getSecurityService()
    {
        return securityService;
    }

    public PersistencyService getPersistencyService()
    {
        return persistencyService;
    }

    public RecordService getRecordService()
    {
        return recordService;
    }

    public DispatcherService getDispatcherService()
    {
        return dispatcherService;
    }

    public static class Builder
    {
        private SecurityService securityService;
        private PersistencyService persistencyService;
        private RecordService recordService;
        private DispatcherService dispatcherService;

        public Builder setSecurityService(SecurityService securityService)
        {
            this.securityService = securityService;
            return this;
        }

        public Builder setPersistencyService(PersistencyService persistencyService)
        {
            this.persistencyService = persistencyService;
            return this;
        }

        public Builder setRecordService(RecordService recordService)
        {
            this.recordService = recordService;
            return this;
        }

        public Builder setDispatcherService(DispatcherService dispatcherService)
        {
            this.dispatcherService = dispatcherService;
            return this;
        }

        public SystemServices build()
        {
            return new SystemServices(this);
        }
    }
}

这是创建 SystemServices 实例的接口(interface):

public interface ServiceProvider
{
    public static SystemServices systemServices = new SystemServices.Builder()
            .setSecurityService(new SecurityService())
            .setPersistencyService(new PersistencyService(new BlackBoxDb(BlackboxApplication.getAppContext())))
            .setRecordService(new RecordService()).setDispatcherService(new DispatcherService()).build();
}

现在我只需使用 systemServices.getSecurityService.doSomethingSecurityRelated() 即可访问每个类中的对象

该代码可以工作，并且对于我这个初学者来说似乎太好了，但我确信这种方法有一些丑陋的地方。所以任何批评都是值得赞赏的:)另外，JVM 如何处理接口(interface)也很有趣。它真的只是一个(一吨)对象还是为每个类创建一个对象？

Answer 1

JVM 会按照你想要的方式处理接口(interface)，只会创建一个 SystemServices。但你所描述的方法确实被认为是“丑陋的”。我认为最好的方法是使用像 Spring 这样的依赖注入(inject)框架。它非常擅长满足您的需求——拥有其他类可以访问的全局对象。它还使测试变得更加容易，并且还使您能够快速更改应使用的全局对象。