什么时候在 Spring 中使用 javax.inject.Provider? [英] When to use javax.inject.Provider in Spring?

问题描述

它的作用很简单:

@Inject
private Provider<ProductService> productService;

产品服务可通过 productService.get() 获得，.get() 将在每次调用时从 Spring 上下文解析实例.

The Product service is available through productService.get() and .get() will resolve the instance from the Spring context on each call.

但是我应该什么时候使用它呢?在哪里?

But when should I use it? And where?

我的主要用例非常简单:当我获得循环依赖时，提供程序会在运行时帮助解决依赖关系.但是，如果您在因循环依赖而无法创建上下文时将其放入，则它看起来有点随机.

My main use case is pretty simple: When I get circular dependencies, the provider helps to resolve the dependency at runtime. But it looks a bit random if you throw it in just when you can't create your context caused by a circular dependency.

是否有任何已知的 Provider 使用模式?

Are there any known patterns about the usage of Providers?

推荐答案

这个接口相当于org.springframework.beans.factory.ObjectFactory，通常用来避免BeanFactory.getBean() 在寻找原型实例时调用客户端代码.通常与 ObjectFactoryCreatingFactoryBean 一起使用以获取由 BeanFactory 获取的原型 bean.

This interface is equivalent to org.springframework.beans.factory.ObjectFactory<T> that is typically used to avoid BeanFactory.getBean() calls in client code when looking for prototype instances. Often used with ObjectFactoryCreatingFactoryBean to get prototypes beans sourced by the BeanFactory.

来自 ObjectFactoryCreatingFactoryBean javadocs 的示例:

example from ObjectFactoryCreatingFactoryBean javadocs:

<beans>

   <!-- Prototype bean since we have state -->
   <bean id="myService" class="a.b.c.MyService" scope="prototype"/>

   <bean id="myServiceFactory"
       class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean">
     <property name="targetBeanName"><idref local="myService"/></property>
   </bean>

   <bean id="clientBean" class="a.b.c.MyClientBean">
     <property name="myServiceFactory" ref="myServiceFactory"/>
   </bean>

</beans>

使用 Providers，您可以使用 ProviderCreatingFactoryBean 代替.

With Providers, you can use the ProviderCreatingFactoryBean instead.

解决相同问题的其他选项，(使用继承代替组合)是查找方法注入

Other option to solve the same problem, (using inheritance instead composition) is the lookup method injection

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