Spring注解之@Import的简单介绍_开发_开发者

普通类

被导入的类会被容器注册成一个Bean，可以被依赖注入使用。【4.2 版本之前只可以导入配置类；4.2版本之后也可以导入普通类，导入的类会被当作配置类】

@Import注册一个类时，这个配置类不应该被@Component或者@Configuration注解标记。Spring中会将所有的bean class封装成一个ConfigurationClass，并且此后会判断被封装的bean class是否是由其他类导入的.

@Configuration
<strong>@Import(OtherBean.</strong><strong>class)
</strong>public class SpringConfig { }

public class OtherBean { }

ImportSelector实现类

实现类不会被注册成Bean，接口方法的返回值会被注册成Bean。【BeanName是全类名】

@Configuration
<strong>@Import(MyImportSelector.</strong><strong>class)
</strong>public class SpringConfig { }

public class MyImportSelector implements<strong> ImportSelector</strong> {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new String[]{OtherBean.class.getName()};
    }
}

DeferredImportSelector实现类

DeferredImportSelector是ImportSelector的子接口, 所以它们的实现方式一样，只是Spring的处理方式不同。DeferredImportSelector和SpringBoot中自动导入配置文件的延迟导入有关。

@Configuration
<strong>@Import(MyDeferredImportSelector.</strong><strong>class)
</strong>public class SpringConfig { }

public class MyDeferredImportSelector implemehttp://www.devze.comnts<strong> DeferredImportSelector</strong> {
    @Override
    public String[] selectImports(AnnotationMetadata importingClassMetadata) {
        return new Sphptring[]{OtherBean.class.getName()};
    }
}

ImportBeanDefinitionRegistrar实现类

实现类不会被注册为bean，但是会回调其接口方法，由开发者通过Spring api手动向Spring容器注册bean。【类似于BeanFactoryPostRegister】

@Configuration
<strong>@Import(MyImportBeanDefinitionRegistrar.</strong><strong>class)
</strong>public class SpringConfig { }

public class MyImportBeanDefinitionRegistrar implements<strong> ImportBeanDefinitionRegistrar</strong> {
    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefjsinitionRegistry registry) {
        BeanDefinition beanDefinition = new RootBeanDefinition();
        String beanName = StringUtils.uncapitalize(OtherBean.class.getSimpleName());
        beanDefinition.setBeanClassName(OtherBean.class.getName());
        registry.registerBeanDefinition(beanName,beanDefinition);
    }
}

附：@Import相关源码解析

加载解析@Import注解位于BeanFactoryPostProcessor处理的时候：

AbstractApplicationContext的refresh方法

-> invokeBeanFactoryPostProcessors(beanFactory);

-> PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());

-> registryProcessor.postProcessBeanDefinitionRegistry(registry);

这里的registryProcessor,我们指ConfigurationClassPostProcessor

ConfigurationClassPostProcessor.postProcessBeanDefinitionRegistry(registry)

-> processConfigBeanDefinitions(registry):

public void processConfigBeanDefinitions(BeanDefinitionRegistry registry) {
    //省略一些配置检查与设置的逻辑

    //根据@Order注解，排序所有的@Configuration类
    configCandidates.sort((bd1, bd2) -> {
			int i1 = ConfigurationClassUtils.getOrder(bd1.getBeanDefinition());
			int i2 = ConfigurationClassUtils.getOrder(bd2.getBeanDefinition());
			return Integer.compare(i1, i2);
		});

	// 创建ConfigurationClassParser解析@Configuration类
	ConfigurationClassParser parser = new ConfigurationClassParser(
			this.metadataReaderFactory, this.problemReporter, this.environment,
			this.resourceLoader, this.componentScanBeanNameGenerator, registry);

    //剩余没有解析的@Configuration类
	Set<BeanDefinitionHolder> candidates = new LinkedHashSet<>(configCandidates);
	//已经解析的@Configuration类
	Set<ConfigurationClass> alreadyParsed = new HashSet<>(configCandidates.size());
	do {
	    /开发者_Python/解析
		parser.parse(candidates);
		parser.validate();

		Set<ConfigurationClass> configClasses = new LinkedH编程客栈ashSet<>(parser.getConfigurationClasses());
		configClasses.removeAll(alreadyParsed);

		// 生成类定义读取器读取类定义
		if (this.reader == null) {
			this.reader = new ConfigurationClassBeanDefinitionReader(
					registry, this.sourceExtractor, this.resourceLoader, this.environment,
					this.importBeanNameGenerator, parser.getImportRegistry());
		}
		this.reader.loadBeanDefinitions(configClasses);
		alreadyParsed.addAll(configClasses);

		candidates.clear();
		if (registry.getBeanDefinitionCount() > candidateNames.length) {
			//省略检查是否有其他需要加载的配置的逻辑
		}
	}
	while (!candidates.isEmpty());

	//省略后续清理逻辑
}

其中parser.parse(candidates)的逻辑主要由org.springframework.context.annotation.ConfigurationClassParser实现，功能是加载@Import注解还有即系@Import注解。reader.loadBeanDefinitions(configClasses);的逻辑主要由org.springframework.context.annotation.ConfigurationClassBeanDefinitionReader的loadBeanDefinitionsForConfigurationClass方法实现，功能是将上面解析的配置转换为BeanDefinition就是Bean定义。