java – @Import注释的用例是什么？

根据official doc：

Annotation Type Configuration

Indicates that a class declares one or more @Bean methods and may be
processed by the Spring container to generate bean deFinitions…

@Configuration classes may be composed using the @Import annotation,
not unlike the way that works in Spring XML. Because
@Configuration objects are managed as Spring beans within the
container..

但我也可以在没有@Import的情况下使用@Configuration注释.我已经测试了下面列出的代码,它按预期工作.那么使用@Import的目的是什么？

dispatcherServletinitializer

public class ApplicationInitializer extends AbstractAnnotationConfigdispatcherServletinitializer {

    @Override
    protected ClassfigClasses() {
        return new Classfig.class };
    }

    @Override
    protected ClassfigClasses() {
        return null;
    }

    @Override
    protected String[] getServletMappings() {
        return new String[] { "/" };
    }

 }

WebMvcConfigurerAdapter

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = { "package.name" })
// @Import(OptionalConfig.class) 
public class WebConfig extends WebMvcConfigurerAdapter {
    // ...
}

OptionalConfig

@Configuration
public class OptionalConfig {

    @Bean(name = "myClass")
    public MyClass myClass() {
        return new MyClass();
    }
}

服务

@Service
public class MyServiceImpl implements MyService {

    @Autowired
    private MyClass myClass;    // yes,it works

    // ...
}

最佳答案

Thus far,we’ve seen how to break up bean deFinitions into multiple @Configuration classes and how to reference those beans across @Configuration boundaries. These scenarios have required providing all @Configuration classes to the constructor of a JavaConfigApplicationContext,and this is not always ideal. Often it is preferable to use an aggregation approach,where one @Configuration class logically imports the bean deFinitions defined by another.

The @Import annotation provides just this kind of support,and it is the direct equivalent of the element found in Spring beans XML files.

http://docs.spring.io/spring-javaconfig/docs/1.0.0.M4/reference/html/ch04s03.html

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