Singleton Bean实例通过泛型参数 [英] Singleton Bean instance by generic parameter

问题描述

我想通过基于单个 @Component 泛型类的泛型参数来创建单例bean实例。

< （我正在使用Spring 4）。

我的代码：

  public interface Mapper< I， O> {
 ... 
} 
  

它的多重实现是Spring @Component s（单身人士）。类似这样：

  @Component 
 public class MapperA实现Mapper< ClazzAI，ClazzAO> {
 ... 
} 
  

和

  @Component 
 public class MapperB实现Mapper< ClazzBI，ClazzBO> {
 ... 
} 
  

其中 ClazzAI ， ClazzAO ， ClazzBI 和 ClazzBO @Component （singleton），它有一个<$ c
$ b $ pre $ $ $ $ $ $ $ $ $ $ $ $ $ $ code> @Component
public class TransformerImpl< I，O，M扩展Mapper< I，O>> {

/ **映射器* /
保护的最终M映射器;

@Inject
private TransformerImpl（final M mapper）{

this.mapper = mapper;
}

...
}


我想这样使用它：

  @Inject 
 private TransformerImpl< ClazzAI，ClazzAO，MapperA> transformerA; 
 
 @Inject 
 private TransformerImpl< ClazzBI，ClazzBO，MapperB> transformerB; 
  

---

问题：

但Spring无法实例化这两个对象，因为它找到了两个 Mapper 实现： MapperA 和 MapperB ，即使我指定了我希望作为通用参数的实现。

任何想法如何无需在 @Configuration class ？

$ b $中实例化所有这些bean b

解决方案

您需要一个单身人士，但需要两个注射点

  @Inject 
 private TransformerImpl< ClazzAI，ClazzAO，MapperA> transformerA; 
 
 @Inject 
 private TransformerImpl< ClazzBI，ClazzBO，MapperB> transformerB; 
  

用于不同构造的对象。这没有什么意义。

你现在意识到你需要两个豆子。如果你不能（不想）在 @Configuration 类中使用 @Bean 工厂方法，你需要声明（并扫描）两个单独的 @Component 类。 （我把你的父构造器公开在这里）。

$ b $ p
class MapperATransformerImpl extends TransformerImpl< ClazzAI，ClazzAO，MapperA> ; {
@Inject
public MapperATransformerImpl（MapperA mapper）{
super（mapper）;
}
}

@Component
class MapperBTransformerImpl扩展了TransformerImpl< ClazzBI，ClazzBO，MapperB> {
@Inject
public MapperBTransformerImpl（MapperB mapper）{
super（mapper）;
}
}

处理注入目标时

  @Inject 
 private TransformerImpl< ClazzAI，ClazzAO，MapperA> transformerA; 
  

Spring会找到 MapperATransformerImpl ，它是类型为 TransformerImpl 并注入。

I would like to have a singleton bean instance by generic parameter based on a single @Component generic class.

(I am using Spring 4.)

My code :

I have an interface like this :

public interface Mapper<I, O> {
    ...
}

And multiple implementation of it which are Spring @Components (singletons). Something like this :

@Component
public class MapperA implements Mapper<ClazzAI, ClazzAO> {
    ...
}

and

@Component
public class MapperB implements Mapper<ClazzBI, ClazzBO> {
    ...
}

where ClazzAI, ClazzAO, ClazzBI and ClazzBO are basic Java classes.

I have another Spring @Component (singleton) which have a Mapper class as a generic parameter :

@Component
public class TransformerImpl<I, O, M extends Mapper<I, O>> {

    /** The Mapper */
    protected final M mapper;

    @Inject
    private TransformerImpl(final M mapper) {

        this.mapper= mapper;
    }

    ...
}

and I would like to use it like this :

@Inject
private TransformerImpl<ClazzAI, ClazzAO, MapperA> transformerA;

@Inject
private TransformerImpl<ClazzBI, ClazzBO, MapperB> transformerB;

---

The problem :

But Spring is not able to instantiate those 2 objects because it founds 2 implementations of Mapper : MapperA and MapperB even if I specify which implementation I want as a generic parameter.

Any idea how to make it without the need of instantiate all of those beans in a @Configuration class ?

解决方案

You're asking for a singleton but requiring two injection points

@Inject
private TransformerImpl<ClazzAI, ClazzAO, MapperA> transformerA;

@Inject
private TransformerImpl<ClazzBI, ClazzBO, MapperB> transformerB;

for differently constructed objects. That doesn't make much sense.

You now realize you need two beans. If you can't (don't want to) do it in a @Configuration class with @Bean factory methods, you'll need to declare (and scan) two separate @Component classes. (I made your parent constructor public here.)

@Component
class MapperATransformerImpl extends TransformerImpl<ClazzAI, ClazzAO, MapperA> {
    @Inject
    public MapperATransformerImpl(MapperA mapper) {
        super(mapper);
    }
}

@Component
class MapperBTransformerImpl extends TransformerImpl<ClazzBI, ClazzBO, MapperB> {
    @Inject
    public MapperBTransformerImpl(MapperB mapper) {
        super(mapper);
    }
}

When processing the injection target

@Inject
private TransformerImpl<ClazzAI, ClazzAO, MapperA> transformerA;

Spring will find the MapperATransformerImpl, which is of type TransformerImpl<ClazzAI, ClazzAO, MapperA> and inject that.

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