public interface ImportSelector {
	//返回類的字符串?dāng)?shù)組，也就是要創(chuàng)建的bean的className，比如userService.class.getName()
    //被創(chuàng)建的bean是在其他bean(@Component、@Service等注解修飾的Bean)創(chuàng)建之前創(chuàng)建的
	String[] selectImports(AnnotationMetadata importingClassMetadata);
}

//定義一個業(yè)務(wù)類
public class UserServiceTest {
	public String getUserName(){
		return "測試";
	}
}
//實(shí)現(xiàn)ImportSelector接口
public class MyImportSelect implements ImportSelector {
	@Override
	public String[] selectImports(AnnotationMetadata importingClassMetadata) {
		//返回要注冊到Spring容器的Class集合
		return new String[]{UserServiceTest.class.getName()};
	}
}
//配置類
@Configuration
@Import(MyImportSelect.class) //導(dǎo)入我們實(shí)現(xiàn)ImportSelector的類。
public class AppConfigClassTest {
}

public class MainTest {
	public static void main(String[] args) {
		AnnotationConfigApplicationContext AnnotationConfigApplicationContext = new AnnotationConfigApplicationContext(AppConfigClassTest.class);
		//這里我們不能通過“userServiceTest”來獲取bean,因?yàn)檫@個bean的name不是userServiceTest，而是userServiceTest.getClass().getName()
        //因?yàn)閎ean的別名成功器，只是針對像注解@Service等注解，會生成一個首字母小寫的BeanName
		UserServiceTest userServiceTest = AnnotationConfigApplicationContext.getBean(UserServiceTest.class);
		System.out.println(((UserServiceTest)userServiceTest).getUserName());
	}
}

//這里就直接跳到ConfigurationClassPostProcessor處理@Import注解的邏輯上
private void processImports(ConfigurationClass configClass, SourceClass currentSourceClass, 
                Collection<SourceClass> importCandidates, Predicate<String> exclusionFilter, boolean checkForCircularImports) {
    //如果importCandidates為空直接return,為什么會有這個，因?yàn)橄旅娲a可能會遞歸調(diào)用processImports，就比如Import一個類，這個類也帶了@Import注解，那就會在調(diào)用一次processImports方法
    if (importCandidates.isEmpty()) {
        return;
    }
    for (SourceClass candidate : importCandidates) {
        if (candidate.isAssignable(ImportSelector.class)) {
        	//1、import的類，實(shí)現(xiàn)了ImportSelector接口
            Class<?> candidateClass = candidate.loadClass();
            //利用反射Class實(shí)例化對象，這個對象不是代理對象不要搞混了。
            ImportSelector selector = ParserStrategyUtils.instantiateClass(candidateClass, ImportSelector.class,
                    this.environment, this.resourceLoader, this.registry);
            Predicate<String> selectorFilter = selector.getExclusionFilter();
            if (selectorFilter != null) {
                exclusionFilter = exclusionFilter.or(selectorFilter);
            }
            if (selector instanceof DeferredImportSelector) {
                this.deferredImportSelectorHandler.handle(configClass, (DeferredImportSelector) selector);
            } else {
            	//調(diào)用ImportSelector接口里面的selectImports方法，拿到返回值Class集合。在通過遞歸的方式嗲用processImports挨個解析每一個Class
                String[] importClassNames = selector.selectImports(currentSourceClass.getMetadata());
                //轉(zhuǎn)成SourceClass集合
                Collection<SourceClass> importSourceClasses = asSourceClasses(importClassNames, exclusionFilter);
                //再次調(diào)用processImports方法
                processImports(configClass, currentSourceClass, importSourceClasses, exclusionFilter, false);
            }
        } else if (candidate.isAssignable(ImportBeanDefinitionRegistrar.class)) {
           。。。。。。
        } else {
            //3、ImportSelector和ImportBeanDefinitionRegistrar都沒有實(shí)現(xiàn)
            this.importStack.registerImport(currentSourceClass.getMetadata(), candidate.getMetadata().getClassName());
            //進(jìn)一步解析其他注解，比如@Component @Import等最后會把configClass注冊到Spring容器中。
            processConfigurationClass(candidate.asConfigClass(configClass), exclusionFilter);
        }
    }
}

//創(chuàng)建實(shí)例對象
static <T> T instantiateClass(Class<?> clazz, Class<T> assignableTo, Environment environment, ResourceLoader resourceLoader, BeanDefinitionRegistry registry) {
	ClassLoader classLoader = 
	       (registry instanceof ConfigurableBeanFactory ? ((ConfigurableBeanFactory) registry).getBeanClassLoader() : resourceLoader.getClassLoader());
	T instance = (T) createInstance(clazz, environment, resourceLoader, registry, classLoader);
	ParserStrategyUtils.invokeAwareMethods(instance, environment, resourceLoader, registry, classLoader);
	return instance;
}
//調(diào)用createInstance方法創(chuàng)建實(shí)例對象
private static Object createInstance(Class<?> clazz, Environment environment, ResourceLoader resourceLoader, BeanDefinitionRegistry registry, @Nullable ClassLoader classLoader) {
	Constructor<?>[] constructors = clazz.getDeclaredConstructors();
	。。。。。。。
	return BeanUtils.instantiateClass(clazz);//通過Bean的工具類生成實(shí)例對象
}