在抽象基类中使用@autowired [英] use @autowired in abstract base class

问题描述

据我所知，不推荐字段注入。应该使用构造函数。

As I know, field injection is not recommended. Should use constructor instead.

我在这里尝试做的是使用 @在基类的构造函数中自动装入，并使其可供所有子类访问。在某些子类中，我还需要一些特定的bean来自它们的构造函数 @Autowired 。演示代码如下：

What I'm trying to do here is using @Autowired in the constructor of the base class, and make it accessible for all the subclasses. In some subclasses, I also need some specific beans to be @Autowired from their constructors. Demo code is as following:

基类：

public abstract class Base {

    protected final MyDemoService myDemoService;

    @Autowired
    public Base(MyDemoService myDemoService) {
        this.myDemoService = myDemoService;
    }
}

继承（子）类：

public class Sub extends Base {

    private final MySubService mySubService;

    @Autowired
    public Sub(MySubService mySubService) {
        this.mySubService = mySubService;
    }
} 

这将给我一个'无默认构造函数'错误。

类似于以下问题：类似的问题和答案，但它在这里不起作用。

This will give me a 'no default constructor' error.
It's similar to the question: similar question and answer, but it doesn't work here.

我已经潜入了一段时间，我发现这篇文章关于依赖注入：进一步阅读

I have dived into this for a while, I found this article about dependency injection: further read

我认为 Setter Injection 是我问题的正确方法吗？

I'm thinking is the Setter Injection a right way for my question?

Setter注入：

public abstract class Base {

    protected MyDemoService myDemoService;

    @Autowired
    public void setMyDemoService(MyDemoService myDemoService) {
        this.myDemoService = myDemoService;
    }
}

我是Java Spring Boot的新手，并且想要从你们那里获得一些专业知识。任何讨论都将受到高度赞赏！

I'm new to Java Spring Boot, and want to get some expertise advise from you guys. Any discussion will be highly appreciated!

推荐答案

您提供的代码将无法编译。只要在您的基类中没有默认构造函数，就应该在子代中调用 super（MyDemoService）。

The code that you provide won't compile. As long as in your base class you don't have the default constructor, you should call super(MyDemoService) in child.

继承（子）类：

public class Sub extends Base {

    private final MySubService mySubService;

    @Autowired
    public Sub(MySubService mySubService, MyDemoService myDemoService){
        super(myDemoService);
        this.mySubService = mySubService;
    }
} 

或者，如果 MySubService 是 MyDemoService的实现

@Autowired
public Sub(MySubService mySubService){
    super(mySubService);
}

只要您的字段 MyDemoService myDemoService 在抽象类中是 protected 你可以在子类中使用它。

As long as your field MyDemoService myDemoService in abstract class is protected you can use it in subclasses.

如果你有多个实现 MyDemoService ，而不是必须使用<$ href =https：// stackoverflow中所述的 @Qualifier 。 com / questions / 26453618 / autowire-distinct-beans-in-abstract-class / 26454131＃26454131>你提到的答案。

If you have multiple implementation of MyDemoService, than you have to use @Qualifier as described in the answer that you have mentioned.

public Sub(@Qualifier("MySubService") MyDemoService mySubService){
    super(mySubService);
}

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