在Spring框架中使用@Import和@ImportResource注释有什么区别？

Question

I am studying for the Spring Core certification and I have a doubt related to the @import and the @importresource annotations use.

So for example I have a configuration class named RootConfig.java , this one:

@Configuration
@Import({AppConfig.class,DbConfig.class})
@ImportResource("classpath:/config/security-config.xml")
@EnableTransactionManagement
public class RootConfig {

}

So I know that in this example the:

@Import({AppConfig.class,DbConfig.class})

are importing 2 others configuration classes (something like including these configurations into the main configuration represented by my RootConfig.java configuration class.

Ant I understand that the:

@ImportResource("classpath:/config/security-config.xml")

are importing an XML file.

So my doubt is: why exist 2 differents annotations that do a very similar task? Why don't use a single annotation to import both configurations classes and resources (such as xml files or property files?)

This is only a semantic differentiation or there are something else?

Answer 1

• @Import

  Indicates one or more @Configuration classes to import. For import Java code-based configuration. eg

   @Configuration @Import({ DataSourceConfig.class, TransactionConfig.class }) public class AppConfig { ... } 

  ^{See more in Using the @Import annotation .}

• @ImportResource

  Indicates one or more resources containing bean definitions to import. For import XML-based configuration or other non- @Configuration bean definition resources. eg

   @Configuration @ImportResource({"classpath:spring-security.xml"}) public class SecurityConfig { ... } 

  ^{See more in @Configuration class-centric use of XML with @ImportResource .}

Answer 2

@ImportResource is meant to be used in java-centric configuration context. The docs say,

In applications where @Configuration classes are the primary mechanism for configuring the container, it will still likely be necessary to use at least some XML. In these scenarios, simply use @ImportResource and define only as much XML as is needed. Doing so achieves a "Java-centric" approach to configuring the container and keeps XML to a bare minimum.

One important aspect is that when using @ImportResource XML configuration you can override the java-centric configuration using the @Bean annotation. This means that you can override the configuration (by changing the configuration XML) without impacting the code. This semantic gives you one context where you can consider using @ImportResource , and its in my view a very valuable asset 'cause one of the most common critique of the java-centric configuration is that it requires code recompile.

The second context is providing the means to gradually move from the XML centric to a java-centric configuration.