@Service批注应保存在哪里?接口还是实现? [英] Where should @Service annotation be kept? Interface or Implementation?

问题描述

我正在使用Spring开发应用程序.我需要使用@Service批注.我有ServiceI和ServiceImpl这样的ServiceImpl implements ServiceI.我对在哪里保留@Service批注感到困惑.

I'm developing an application using Spring. I'm required to use the @Service annotation. I have ServiceI and ServiceImpl such that ServiceImpl implements ServiceI. I'm confused here as to where should I keep the @Service annotation.

我应该用@Service注释接口或实现吗?这两种方法有什么区别?

Should I annotate the interface or the implementation with @Service? What are the differences between these two approaches?

推荐答案

我从不在接口上放置@Component(或@Service，...)，因为这会使该接口无用.让我解释一下原因.

I never put @Component (or @Service, ...) at an interface, because this make the interface useless. Let me explain why.

声明1::如果您有一个接口，则想将该接口用于注入点类型.

claim 1: If you have an interface then you want to use that interface for the injection point type.

声明2::接口的目的是定义可以由多种实现方式实现的契约.在另一侧，您有注入点(@Autowired). (IMHO)仅具有一个接口和仅一个实现该接口的类是无用的，并且违反了 YAGNI .

claim 2: The purpose of an interface is that it define a contract that can been implemented by several implementations. On the other side you have your injection point (@Autowired). Having just one interface and only one class that implement it, is (IMHO) useless, and violates YAGNI.

事实:放置时间:

• @Component(或@Service，...)在接口上，
• 具有多个实现它的类，
• 至少有两个类成为Spring Bean，并且
• 有一个注入点，该注入点使用该接口进行基于类型的注入，

• @Component (or @Service, ...) at an interface,
• have multiple classes that implements it,
• at least two classes become Spring Beans, and
• have an injection point that use the interface for type based injection,

然后您将得到NoUniqueBeanDefinitionException (或者您有一个非常特殊的配置设置，包括环境，配置文件或限定符...)

then you will get and NoUniqueBeanDefinitionException (or you have a very special configurations setup, with Environment, Profiles or Qualifiers ...)

结论:如果在接口上使用@Component(或@Service，...)，则必须违反两个规则中的至少一个.因此，我认为将@Component放在接口级别上是没有用的(在某些罕见情况下除外).

Conclusion: If you use @Component (or @Service, ...) at an interface then you must violate at least one of the two clains. Therefore I think it is not useful (except some rare scenarios) to put @Component at interface level.

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