无法在Spring中继承@Component? [英] Can't get @Component to be inherited in Spring?

问题描述

在我的项目中有一个所有客户端类都扩展的公共基类.这有一个需要由 Hibernate 注入的 @Autowired 字段.这些都在另一个类中组合在一起，该类具有基类的 @Autowired 集合.

为了减少客户端代码的样板，我试图继承@Component.@Component 默认不这样做(显然 它曾经使用过)，我创建了这个解决方法注释

@Target(ElementType.TYPE)@Retention(RetentionPolicy.RUNTIME)@成分@遗传公共@interface InheritedComponent {}

... 并用它注释基类.它不漂亮，但我希望它会起作用.不幸的是它没有，这真的让我感到困惑，因为@Inherited 应该让它工作

还有其他方法可以继承@Component吗?或者我必须说任何扩展基类的类都需要这个样板?

解决方案

问题是Component注解类型本身需要用@Inherited标记.>

您的 @InheritedComponent 注释类型被任何扩展超类的类正确继承，该超类标记为 @InheritedComponent - 但它不继承 @Component.这是因为您在 注释 上有 @Component，而不是父类型.

示例:

公共类 InheritedAnnotationTest {@继承组件公共静态类 BaseComponent {}public static class SubClass extends BaseComponent {}公共静态无效主(字符串 [] args){子类 s = 新子类();for (注解 a : s.getClass().getAnnotations()) {System.out.printf("%s 有注释 %s\n", s.getClass(), a);}}}

输出:

<块引用>

class brown.annotations.InheritedAnnotationTest$SubClass 有注解@brown.annotations.InheritedComponent()

换句话说，当解析一个类有哪些注解时，注解的注解不会被解析——它们不适用于类，只应用于注解(如果有意义的话).

In my project there's a common base class that all client classes extend. This has an @Autowired field that needs to be injected by Hibernate. These are all grouped together in another class that has an @Autowired collection of the base class.

In order to reduce boilerplate for client code I'm trying to get @Component inherited. With @Component not doing this by default (apparently it used to though), I created this workaround annotation

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Component
@Inherited
public @interface InheritedComponent {
}

... and annotated the base class with it. Its not pretty but I hoped it would work. Unfortunately it didn't, which really confuses me as @Inherited should make it work

Is there any other way to get @Component inherited? Or do I just have to say that any class that extends the base class needs this boilerplate?

解决方案

The problem is that the Component annotation type itself needs to be marked with @Inherited.

Your @InheritedComponent annotation type is correctly inherited by any classes that extend a superclass which is marked with @InheritedComponent - but it does not inherit @Component. This is because you have @Component on the annotation, not the parent type.

An example:

public class InheritedAnnotationTest {

    @InheritedComponent
    public static class BaseComponent {
    }

    public static class SubClass extends BaseComponent {
    }

    public static void main(String[] args) {
        SubClass s = new SubClass();

        for (Annotation a : s.getClass().getAnnotations()) {
            System.out.printf("%s has annotation %s\n", s.getClass(), a);
        }
    }
}

Output:

class brown.annotations.InheritedAnnotationTest$SubClass has annotation @brown.annotations.InheritedComponent()

In other words, when resolving what annotations a class has, the annotations of the annotations are not resolved - they do not apply to the class, only the annotation (if that makes sense).

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