Spring注解之@Import的简单介绍

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

public class OtherBean { }

@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()};
    }
}

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

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

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

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

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 {
	    //解析
		parser.parse(candidates);
		parser.validate();

		Set<ConfigurationClass> configClasses = new LinkedHashSet<>(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
}