如何在Spring中创建默认的可重写组件? [英] How to create a default overridable Component in Spring?

问题描述

除非用户创建其他实现，否则我将尝试创建一个将为Autowired的Component. 我使用以下代码来尝试解决问题:

I am trying to create a Component that will be Autowired unless the user creates a different implementation. I used the following code to try and isolate the problem:

界面:

public interface A {...}

实现:

@Component
@ConditionalOnMissingBean(A.class)
public class AImpl implements A {...}

使用代码:

public class AUsage {
    @Autowired
    private A a;
}

在此示例中，我没有将AImpl自动装配到AUsage中. 如果我在没有ConditionalOnMissingBean的另一个类中实现了A，则可以正常工作.

In this example, I don't get AImpl autowired into AUsage. If I implement A in another class without the ConditionalOnMissingBean it works.

推荐答案

我尝试从Internet复制@ConditionalOnMissingBean的现有用法，并注意到它们都引用了@Bean方法.

I tried copying existing uses of @ConditionalOnMissingBean from the internet and noticed that they all reference a @Bean method.

确实，当我将此代码添加到AUsage:

Indeed, when I added this code to AUsage:

public class AUsage {
    @Autowired
    private A a;

    @Bean
    @ConditionalOnMissingBean
    public A createA() {
        return new AImpl();
    }
}

并从AImpl中删除了注释:

and removed the annotations from AImpl:

public class AImpl implements A {...}

一切正常.

如果有人知道，我很乐意对此做一个解释.

I'd be pleased to get an explanation to this, if anyone knows.

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