Java 如何在没有 XML 的情况下使用 Spring 根据属性在运行时注入不同的服务

How to inject different services at runtime based on a property with Spring without XML

提问by Pedro Lopez

I am using Spring Boot for Java standalone application. I have a bean which makes use of a service. I want to inject different implementations of that service at runtime, based on a property in a properties file with Spring (4 for that matter).

我正在将 Spring Boot 用于 Java 独立应用程序。我有一个使用服务的 bean。我想在运行时注入该服务的不同实现，基于 Spring 的属性文件中的属性（就此而言为 4）。

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This sounds like the Factory pattern, but Spring also allows using annotations to solve the problem, like this.

这听起来像工厂模式，但 Spring 也允许使用注解来解决问题，就像这样。

@Autowired @Qualifier("selectorProperty") private MyService myService;

Then in the beans.xml file I have an alias, so that I can use the property in the @Qualifier.

然后在 beans.xml 文件中我有一个别名，以便我可以使用@Qualifier 中的属性。

<alias name="${selector.property}" alias="selectorProperty" />

And in my different implementations I would have different qualifiers.

在我的不同实现中，我会有不同的限定符。

@Component("Selector1")
public class MyServiceImpl1

@Component("Selector2")
public class MyServiceImpl2

application.properties

应用程序属性

selector.property = Selector1

selector.property = Selector2

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Whereas regarding the factory pattern, in Spring you can use ServiceLocatorFactoryBean to create a factory that would give you the same functionality.

而关于工厂模式，在 Spring 中，您可以使用 ServiceLocatorFactoryBean 创建一个工厂，该工厂将为您提供相同的功能。

<bean
  class="org.springframework.beans.factory.config.ServiceLocatorFactoryBean"
  id="myServiceFactory">
  <property
    name="serviceLocatorInterface"
    value="my.company.MyServiceFactory">
  </property>
</bean>

public interface MyServiceFactory
{
    MyService getMyService(String selector);
}

And then in your bean you can use something like this to get the right implementation at runtime depending on the value of the property.

然后在你的 bean 中，你可以使用这样的东西在运行时根据属性的值获得正确的实现。

@Value("${selector.property}") private String selectorProperty;

@Autowired private MyServiceFactory myServiceFactory;

private MyService myService;

@PostConstruct
public void postConstruct()
{
    this.myService = myServiceFactory.getMyService(selectorProperty);
}

But the problem with this solution is that I could not find a way to avoid using XML to define the factory, and I would like to use only annotations.

但是这个解决方案的问题是我找不到避免使用 XML 定义工厂的方法，我只想使用注释。

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So the question would be, is there a way to use the ServiceLocatorFactoryBean (or something equivalent) using only annotations, or am I forced to use the @Autowired @Qualifier way if I do not want to define beans in XML? Or is there any other way to inject different services at runtime based on a property with Spring 4 avoiding XML? If your answer is just use the @Autowired @Qualifierwith the alias, please give a reason why that is better than using a well known factory pattern.

所以问题是，有没有办法只使用注释来使用 ServiceLocatorFactoryBean（或等效的东西），或者如果我不想在 XML 中定义 bean，我是否被迫使用 @Autowired @Qualifier 方式？或者有没有其他方法可以在运行时基于 Spring 4 避免 XML 的属性注入不同的服务？如果您的答案只是使用@Autowired @Qualifier别名，请说明为什么这比使用众所周知的工厂模式更好。

Using the extra XML is forcing me to use @ImportResource("classpath:beans.xml")in my Launcher class, which I'd rather not use either.

使用额外的 XML 迫使我@ImportResource("classpath:beans.xml")在我的 Launcher 类中使用，我也不想使用它。

Thanks.

谢谢。

采纳答案by Pedro Lopez

Actually, you can use ServiceLocatorFactory without XML by declaring it as a bean in your configuration file.

实际上，您可以通过在配置文件中将 ServiceLocatorFactory 声明为 bean 来使用没有 XML 的 ServiceLocatorFactory。

@Bean
public ServiceLocatorFactoryBean myFactoryServiceLocatorFactoryBean()
{
    ServiceLocatorFactoryBean bean = new ServiceLocatorFactoryBean();
    bean.setServiceLocatorInterface(MyServiceFactory.class);
    return bean;
}

@Bean
public MyServiceFactory myServiceFactory()
{
    return (MyServiceFactory) myFactoryServiceLocatorFactoryBean().getObject();
}

Then you can still use the factory as usual, but no XML is involved.

然后你仍然可以像往常一样使用工厂，但不涉及 XML。

@Value("${selector.property}") private String selectorProperty;

@Autowired @Qualifier("myServiceFactory") private MyServiceFactory myServiceFactory;

private MyService myService;

@PostConstruct
public void postConstruct()
{
    this.myService = myServiceFactory.getMyService(selectorProperty);
}

回答by mavarazy

I'm using Spring profiles

我正在使用 Spring 配置文件

For example with dataSources Using it you can define as many dataSources, as you like

例如使用 dataSources 使用它，您可以根据需要定义任意数量的数据源

@Configuration
@Profile("dev")
public class StandaloneDataConfig {

    @Bean
    public DataSource dataSource() {
        return new EmbeddedDatabaseBuilder()
            .setType(EmbeddedDatabaseType.HSQL)
            .addScript("classpath:com/bank/config/sql/schema.sql")
            .addScript("classpath:com/bank/config/sql/test-data.sql")
            .build();
    }

}

@Configuration
@Profile("cloud")
public class CloudDataConfig {

    @Bean
    public DataSource dataSource() {
        return new EmbeddedDatabaseBuilder()
            .setType(EmbeddedDatabaseType.HSQL)
            .addScript("classpath:com/bank/config/sql/schema.sql")
            .addScript("classpath:com/bank/config/sql/test-data.sql")
            .build();
    }

}

And in runtime, by specifying

在运行时，通过指定

-Dspring.profiles.active="myProfile"

-Dspring.profiles.active="myProfile"

you active one or another configuration (All of them must be imported in your main Configuration, they are just ignored based on active profile).

您激活一个或另一个配置（所有这些都必须在您的主配置中导入，它们只是根据活动配置文件被忽略）。

Here is a good article: http://spring.io/blog/2011/02/14/spring-3-1-m1-introducing-profile/

这是一篇好文章：http: //spring.io/blog/2011/02/14/spring-3-1-m1-introducing-profile/