java 如何指定 Spring 应该使用哪个子类
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/16938346/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to specify which subclass Spring should use
提问by Kovalsky
In my spring-based project I have a core module ('core') with a class
在我基于 spring 的项目中，我有一个带有类的核心模块（'core'）
@Component
public class Superclass {
// stuff
}
instances of which are injected by type throughout the code like this:
其实例在整个代码中按类型注入，如下所示：
public class AService {
@Autowired
private Superclass superclass;
// service stuff
}
I also have two other modules that depend on the core module and one of which (let's call it 'module1') extends Superclass:
我还有另外两个依赖于核心模块的模块，其中一个（我们称之为“module1”）扩展了Superclass：
@component
public class Subclass extends Superclass {
// overridden stuff
}
The other module ('module2') uses Superclassas is.
另一个模块（'module2'）按原样使用超类。
Now I want that when I compile and run 'child1' an instance of Subclassis used everywhere an instance of Superclassis expected. So I write a configuration class:
现在我希望当我编译和运行 'child1' 时，在任何需要超类实例的地方都使用子类的实例。于是我写了一个配置类：
@Configuration
public class Module2Configuration {
@Bean
public Superclass superclass(){
return new Subclass();
}
}
When I run this I see bothSuperclassandSubclassinstantiated which is definitely notwhat I want. How do specify in 'module1' which type Spring should instantiate?
当我运行此我看到两个超类和子类实例化，这绝对不是我想要的。如何在“module1”中指定 Spring 应该实例化的类型？
回答by michal
You can use @Qualifier("some name") annotation. There is more information about that: http://blogs.sourceallies.com/2011/08/spring-injection-with-resource-and-autowired/
您可以使用 @Qualifier("some name") 注释。有更多相关信息：http: //blogs.sourceallies.com/2011/08/spring-injection-with-resource-and-autowired/
回答by Jens Birger Hahn
Spring eagerly instantiates singleton beans as stated in the documentation:
Spring 急切地实例化单例 bean，如文档中所述：
By default, ApplicationContext implementations eagerly create and configure all singleton beans as part of the initialization process.
默认情况下，ApplicationContext 实现会在初始化过程中急切地创建和配置所有单例 bean。
which might explain why both @Componentsare created.
这可能解释了为什么两者都@Components被创建。
To specifiy which implementation is provided as a dependency you might want to check on Qualifiersthat enable to choose between different implementations. In combination with lazy loading this should do the trick.
要指定作为依赖项提供的实现，您可能需要检查能够在不同实现之间进行选择的限定符。结合延迟加载，这应该可以解决问题。
Depending on your personal taste you could also use delegation instead of inheritance using a separated interface:
根据您的个人品味，您还可以使用委托而不是使用分离接口的继承：
public interface MyService {
public String foobar(int baz);
}
public static class CommonBehavior {
// whatever is used by Superclass and Subclass
}
@Component @Lazy
public class FormerSuperClass implements MyService {
private final CommonBehavior ...;
...
}
@Component @Lazy
public class FormerSubClass implements MyService {
private final CommonBehavior ...;
...
}
Good luck!
祝你好运！
回答by wilbur_zzz
There are 2 methods: Use @Qualifier("SubclassName") Or Mark your subclass as @Component and declare the subclass when @Autowired
有两种方法：使用@Qualifier("SubclassName") 或将您的子类标记为@Component 并在@Autowired 时声明子类
In your case:
在你的情况下：
Use @Qualifier("SubclassName")
@Component public class Superclass { // stuff } @component public class Subclass extends Superclass { // overridden stuff } public class AService { @Autowired @Qualifier("Subclass") private Superclass superclass; // service stuff }
使用@Qualifier("SubclassName")
@Component public class Superclass { // stuff } @component public class Subclass extends Superclass { // overridden stuff } public class AService { @Autowired @Qualifier("Subclass") private Superclass superclass; // service stuff }
2.Mark your subclass as @Component and declare the subclass when @Autowired
2.将你的子类标记为@Component并在@Autowired时声明子类
public class Superclass {
// stuff
}
@component
public class Subclass extends Superclass {
// overridden stuff
}
public class AService {
@Autowired
private Subclass subclass;
// service stuff
}
