面试官：说一说 Spring Boot 自动配置原理吧，我懵逼了...

@Component 	
public class Person { 	

	
@Value("i am name") 	
private String name; 	

	
}

<bean class="Person"> 	
<property name ="name" value="i am name"></property>	
</bean>

person.name=kundy 	
person.age=13 	
person.sex=male

@Component 	
@ConfigurationProperties(prefix = "person") 	
public class Person { 	

	
private String name; 	
private Integer age; 	
private String sex; 	

	
}

public class Circle { 	

	
public void sayHi() { 	
System.out.println("Circle sayHi()"); 	
} 	

	
}

@Import({Circle.class}) 	
@Configuration 	
public class MainConfig { 	

	
}

public static void main(String[] args) { 	

	
ApplicationContext context = new AnnotationConfigApplicationContext(MainConfig.class); 	
Circle circle = context.getBean(Circle.class); 	
circle.sayHi(); 	

	
}

public class Triangle { 	

	
public void sayHi(){ 	
System.out.println("Triangle sayHi()"); 	
} 	

	
}

public class MyImportSelector implements ImportSelector { 	

	
@Override 	
public String[] selectImports(AnnotationMetadata annotationMetadata) { 	
return new String[]{"annotation.importannotation.waytwo.Triangle"}; 	
} 	

	
}

@Import({Circle.class,MyImportSelector.class}) 	
@Configuration 	
public class MainConfigTwo { 	

	
}

public static void main(String[] args) { 	

	
ApplicationContext context = new AnnotationConfigApplicationContext(MainConfigTwo.class); 	
Circle circle = context.getBean(Circle.class); 	
Triangle triangle = context.getBean(Triangle.class); 	
circle.sayHi(); 	
triangle.sayHi(); 	

	
}

public class Rectangle { 	

	
public void sayHi() { 	
System.out.println("Rectangle sayHi()"); 	
} 	

	
}

public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar { 	

	
@Override 	
public void registerBeanDefinitions(AnnotationMetadata annotationMetadata, BeanDefinitionRegistry beanDefinitionRegistry) { 	

	
RootBeanDefinition rootBeanDefinition = new RootBeanDefinition(Rectangle.class); 	
// 注册一个名字叫做 rectangle 的 bean 	
beanDefinitionRegistry.registerBeanDefinition("rectangle", rootBeanDefinition); 	
} 	

	
}

@Import({Circle.class, MyImportSelector.class, MyImportBeanDefinitionRegistrar.class}) 	
@Configuration 	
public class MainConfigThree { 	

	
}

public static void main(String[] args) { 	

	
ApplicationContext context = new AnnotationConfigApplicationContext(MainConfigThree.class); 	
Circle circle = context.getBean(Circle.class); 	
Triangle triangle = context.getBean(Triangle.class); 	
Rectangle rectangle = context.getBean(Rectangle.class); 	
circle.sayHi(); 	
triangle.sayHi(); 	
rectangle.sayHi(); 	

	
}

public class ConditionBean { 	

	
public void sayHi() { 	
System.out.println("ConditionBean sayHi()"); 	
} 	

	
}

public class MyCondition implements Condition { 	

	
@Override 	
public boolean matches(ConditionContext conditionContext, AnnotatedTypeMetadata annotatedTypeMetadata) { 	
return true; 	
} 	

	
}

@Configuration 	
@Conditional(MyCondition.class) 	
public class ConditionConfig { 	

	
@Bean 	
public ConditionBean conditionBean(){ 	
return new ConditionBean(); 	
} 	

	
}

public static void main(String[] args) { 	

	
ApplicationContext context = new AnnotationConfigApplicationContext(ConditionConfig.class); 	
ConditionBean conditionBean = context.getBean(ConditionBean.class); 	
conditionBean.sayHi(); 	

	
}

public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) { 	

	
this.sources = new LinkedHashSet(); 	
this.bannerMode = Mode.CONSOLE; 	
this.logStartupInfo = true; 	
this.addCommandLineProperties = true; 	
this.addConversionService = true; 	
this.headless = true; 	
this.registerShutdownHook = true; 	
this.additionalProfiles = new HashSet(); 	
this.isCustomEnvironment = false; 	
this.resourceLoader = resourceLoader; 	
Assert.notNull(primarySources, "PrimarySources must not be null"); 	
// 保存主配置类（这里是一个数组，说明可以有多个主配置类） 	
this.primarySources = new LinkedHashSet(Arrays.asList(primarySources)); 	
// 判断当前是否是一个 Web 应用 	
this.webApplicationType = WebApplicationType.deduceFromClasspath(); 	
// 从类路径下找到 META/INF/Spring.factories 配置的所有 ApplicationContextInitializer，然后保存起来 	
this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class)); 	
// 从类路径下找到 META/INF/Spring.factories 配置的所有 ApplicationListener，然后保存起来 	
this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class)); 	
// 从多个配置类中找到有 main 方法的主配置类（只有一个） 	
this.mainApplicationClass = this.deduceMainApplicationClass(); 	

	
}

public ConfigurableApplicationContext run(String... args) { 	

	
// 创建计时器 	
StopWatch stopWatch = new StopWatch(); 	
stopWatch.start(); 	
// 声明 IOC 容器 	
ConfigurableApplicationContext context = null; 	
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList(); 	
this.configureHeadlessProperty(); 	
// 从类路径下找到 META/INF/Spring.factories 获取 SpringApplicationRunListeners 	
SpringApplicationRunListeners listeners = this.getRunListeners(args); 	
// 回调所有 SpringApplicationRunListeners 的 starting() 方法 	
listeners.starting(); 	
Collection exceptionReporters; 	
try { 	
// 封装命令行参数 	
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); 	
// 准备环境，包括创建环境，创建环境完成后回调 SpringApplicationRunListeners#environmentPrepared()方法，表示环境准备完成 	
ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments); 	
this.configureIgnoreBeanInfo(environment); 	
// 打印 Banner 	
Banner printedBanner = this.printBanner(environment); 	
// 创建 IOC 容器（决定创建 web 的 IOC 容器还是普通的 IOC 容器） 	
context = this.createApplicationContext(); 	
exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context); 	
/*	
 * 准备上下文环境，将 environment 保存到 IOC 容器中，并且调用 applyInitializers() 方法	
 * applyInitializers() 方法回调之前保存的所有的 ApplicationContextInitializer 的 initialize() 方法	
 * 然后回调所有的 SpringApplicationRunListener#contextPrepared() 方法 	
 * 最后回调所有的 SpringApplicationRunListener#contextLoaded() 方法 	
 */	
this.prepareContext(context, environment, listeners, applicationArguments, printedBanner); 	
// 刷新容器，IOC 容器初始化（如果是 Web 应用还会创建嵌入式的 Tomcat），扫描、创建、加载所有组件的地方 	
this.refreshContext(context); 	
// 从 IOC 容器中获取所有的 ApplicationRunner 和 CommandLineRunner 进行回调 	
this.afterRefresh(context, applicationArguments); 	
stopWatch.stop(); 	
if (this.logStartupInfo) { 	
(new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch); 	
} 	
// 调用 所有 SpringApplicationRunListeners#started()方法 	
listeners.started(context); 	
this.callRunners(context, applicationArguments); 	
} catch (Throwable var10) { 	
this.handleRunFailure(context, var10, exceptionReporters, listeners); 	
throw new IllegalStateException(var10); 	
} 	
try { 	
listeners.running(context); 	
return context; 	
} catch (Throwable var9) { 	
this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null); 	
throw new IllegalStateException(var9); 	
} 	
}

@SpringBootConfiguration 	
@EnableAutoConfiguration 	
@ComponentScan( 	
excludeFilters = {@Filter( 	
type = FilterType.CUSTOM, 	
classes = {TypeExcludeFilter.class} 	
), @Filter( 	
type = FilterType.CUSTOM, 	
classes = {AutoConfigurationExcludeFilter.class} 	
)} 	
) 	
public @interface SpringBootApplication { 	

	
}

@AutoConfigurationPackage 	
@Import({AutoConfigurationImportSelector.class}) 	
public @interface EnableAutoConfiguration {

@Configuration 	
@EnableConfigurationProperties({HttpProperties.class}) 	
@ConditionalOnWebApplication( 	
type = Type.SERVLET 	
) 	
@ConditionalOnClass({CharacterEncodingFilter.class}) 	
@ConditionalOnProperty( 	
prefix = "spring.http.encoding", 	
value = {"enabled"}, 	
matchIfMissing = true 	
) 	
public class HttpEncodingAutoConfiguration { 	

	
}

@ConfigurationProperties( 	
prefix = "spring.http" 	
)// 从配置文件中获取指定的值和bean的属性进行绑定 	
public class HttpProperties { 	
}