标签：data inf hang getc map 配置 tca net dfa
以下源码的 SpringBoot 版本：2.3.9.RELEASE。
分为两大步：
三个注解核心注解：@SpringBootConfiguration，@EnableAutoConfiguration和@ComponentScan。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
根据Javadoc可知，该注解作用就是将当前的类作为一个JavaConfig，然后触发注解@EnableAutoConfiguration和@ComponentScan的处理，本质上与@Configuration注解没有区别。
扫描的 Spring 对应的组件，如 @Componet，@Repository。
我们可以通过 basePackages 等属性来细粒度的定制 @ComponentScan 自动扫描的范围，如果不指定，则默认Spring框架实现会从声明 @ComponentScan 所在类的package进行扫描，所以 SpringBoot 的启动类最好是放在根package下，我们自定义的类就放在对应的子package下，这样就可以不指定 basePackages。
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
Javadoc 可知，多用于导入被 @Conditional 注解的Bean，之后会进行 filter 操作SpringBoot 启动时会调用该方法，进行自动装配的处理，见SpringApplication#run(java.lang.String...)源码解析
spring-boot-autoconfigure jar包下的 META-INF/spring.factories 文件下的配置SpringIOC 容器，自此 SpringBoot 自动装配完成！@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
SpringBoot 自动装配的核心注解，在 Spring 框架中就提供了各种以@Enable开头的注解，例如： @EnableCircuitBreaker、@EnableScheduling等；
@EnableAutoConfiguration，借助@Import的支持，收集和注册特定场景相关的bean定义;
自动装配的类，通常是 @Configuration 类，通过 SpringFactoriesLoader 加载到 Spring 容器。
注册当前启动类的根package；
注册 org.springframework.boot.autoconfigure.AutoConfigurationPackages 的BeanDefinition。
public class AutoConfigurationImportSelector implements DeferredImportSelector, BeanClassLoaderAware,
ResourceLoaderAware, BeanFactoryAware, EnvironmentAware, Ordered {
可以看到实现了 DeferredImportSelector 接口，该接口继承自ImportSelector，根据Javadoc可知，多用于导入被@Conditional注解的Bean
DeferredImportSelector接口中有个process方法，SpringBoot启动时会调用该方法，进行自动装配的处理，大体流程如下：
AutoConfigurationImportSelector.AutoConfigurationGroup#process方法的源码：
调用了AutoConfigurationImportSelector#getAutoConfigurationEntry方法，获取需要自动装配类
public void process(AnnotationMetadata annotationMetadata, DeferredImportSelector deferredImportSelector) {
Assert.state(deferredImportSelector instanceof AutoConfigurationImportSelector,
() -> String.format("Only %s implementations are supported, got %s",
AutoConfigurationImportSelector.class.getSimpleName(),
deferredImportSelector.getClass().getName()));
// 获取需要自动装配类
AutoConfigurationEntry autoConfigurationEntry = ((AutoConfigurationImportSelector) deferredImportSelector)
.getAutoConfigurationEntry(annotationMetadata);
this.autoConfigurationEntries.add(autoConfigurationEntry);
for (String importClassName : autoConfigurationEntry.getConfigurations()) {
this.entries.putIfAbsent(importClassName, annotationMetadata);
}
}
AutoConfigurationImportSelector#getAutoConfigurationEntry大体流程如下：
通过SpringFactoriesLoader#loadFactoryNames获取应考虑的自动配置名称，例如来源于 spring-boot-autoconfigure jar包下的META-INF/spring.factories文件下的配置
通过filter过滤掉当前环境不需要自动装配的类，比如没有集成RabbitMQ，就不需要，或者有的条件@Conditional不满足也不需要自动装配
返回需要自动装配的全路径类名
源码如下：
protected AutoConfigurationEntry getAutoConfigurationEntry(AnnotationMetadata annotationMetadata) {
if (!isEnabled(annotationMetadata)) {
return EMPTY_ENTRY;
}
AnnotationAttributes attributes = getAttributes(annotationMetadata);
// 获取预先定义的应考虑的自动配置类名称
List<String> configurations = getCandidateConfigurations(annotationMetadata, attributes);
configurations = removeDuplicates(configurations);
Set<String> exclusions = getExclusions(annotationMetadata, attributes);
checkExcludedClasses(configurations, exclusions);
configurations.removeAll(exclusions);
// 通过filter过滤掉当前环境不需要自动装配的类，比如没有集成RabbitMQ，就不需要，或者有的条件@Conditional不满足也不需要自动装配
configurations = getConfigurationClassFilter().filter(configurations);
fireAutoConfigurationImportEvents(configurations, exclusions);
// 返回需要自动装配的全路径类名
return new AutoConfigurationEntry(configurations, exclusions);
}
AutoConfigurationImportSelector#getCandidateConfigurations源码如下：
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata, AnnotationAttributes attributes) {
List<String> configurations = SpringFactoriesLoader.loadFactoryNames(getSpringFactoriesLoaderFactoryClass(),
getBeanClassLoader());
Assert.notEmpty(configurations, "No auto configuration classes found in META-INF/spring.factories. If you "
+ "are using a custom packaging, make sure that file is correct.");
return configurations;
}
通过SpringFactoriesLoader#loadFactoryNames获取应考虑的自动配置名称，通过META-INF/spring.factories下的配置，例如：
spring-boot-autoconfigure jar包下的 spring.factories 文件：
执行完configurations = getConfigurationClassFilter().filter(configurations);之后，各种@Conditional不满足就被过滤掉，剩下35个了
可以通过如下方法进行验证，结果没有 RabbitAutoConfiguration 相关的Bean，抛出异常 NoSuchBeanDefinitionException
@SpringBootApplication
public class SpringDemosApplication implements ApplicationContextAware {
private static ApplicationContext applicationContext;
public static void main(String[] args) {
SpringApplication.run(SpringDemosApplication.class, args);
System.out.println(applicationContext.getBean(AopAutoConfiguration.class));
System.out.println(applicationContext.getBean(RabbitAutoConfiguration.class));
}
@Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
SpringDemosApplication.applicationContext = applicationContext;
}
}
main方法里调用org.springframework.boot.SpringApplication#run(java.lang.Class<?>, java.lang.String...)方法
@SpringBootApplication
public class SpringDemosApplication {
public static void main(String[] args) {
SpringApplication.run(SpringDemosApplication.class, args);
}
}
调用另外一个同名的重载方法run
public static ConfigurableApplicationContext run(Class<?> primarySource, String... args) {
return run(new Class<?>[] { primarySource }, args);
}
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return new SpringApplication(primarySources).run(args);
}
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
// 初始化webApplicationType，比如"SERVLET"
this.webApplicationType = WebApplicationType.deduceFromClasspath();
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
// 初始化一些listeners
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
经典的观察者模式，只要你把事件广播的顺序理解了，那整个流程就很容易串起来了：
public ConfigurableApplicationContext run(String... args) {
// 创建一个StopWatch实例，用来记录SpringBoot的启动时间
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
// 通过SpringFactoriesLoader加载listeners：比如EventPublishingRunListener
SpringApplicationRunListeners listeners = getRunListeners(args);
// 发布SprintBoot启动事件：ApplicationStartingEvent
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
// 创建和配置environment，发布事件：SpringApplicationRunListeners#environmentPrepared
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
configureIgnoreBeanInfo(environment);
// 打印SpringBoot的banner和版本
Banner printedBanner = printBanner(environment);
// 创建对应的ApplicationContext：Web类型，Reactive类型，普通的类型(非Web)
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
// 准备ApplicationContext，Initializers设置到ApplicationContext后发布事件：ApplicationContextInitializedEvent
// 打印启动日志，打印profile信息(如dev, test, prod)
// 调用EventPublishingRunListener发布ApplicationContext加载完毕事件：ApplicationPreparedEvent
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
// 最终会调用到AbstractApplicationContext#refresh方法，实际上就是Spring IOC容器的创建过程，并且会进行自动装配的操作
// 以及发布ApplicationContext已经refresh事件，标志着ApplicationContext初始化完成
refreshContext(context);
// hook方法
afterRefresh(context, applicationArguments);
// stopWatch停止计时，日志打印总共启动的时间
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
// 发布SpringBoot程序已启动事件ApplicationStartedEvent
listeners.started(context);
// 调用ApplicationRunner和CommandLineRunner
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
// 最后发布就绪事件ApplicationReadyEvent，标志着SpringBoot可以处理就收的请求了
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
SpringApplicationRunListeners的唯一实现是EventPublishingRunListener;
整个SpringBoot的启动，流程就是各种事件的发布，调用EventPublishingRunListener中的方法。
只要明白了EventPublishingRunListener中事件发布的流程，也就明白了SpringBoot启动的大体流程
方法说明如下：
public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered {
private final SpringApplication application;
private final String[] args;
private final SimpleApplicationEventMulticaster initialMulticaster;
public EventPublishingRunListener(SpringApplication application, String[] args) {
this.application = application;
this.args = args;
this.initialMulticaster = new SimpleApplicationEventMulticaster();
for (ApplicationListener<?> listener : application.getListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
@Override
public int getOrder() {
return 0;
}
// SpringBoot启动事件
@Override
public void starting() {
this.initialMulticaster.multicastEvent(new ApplicationStartingEvent(this.application, this.args));
}
// 创建和配置环境
@Override
public void environmentPrepared(ConfigurableEnvironment environment) {
this.initialMulticaster
.multicastEvent(new ApplicationEnvironmentPreparedEvent(this.application, this.args, environment));
}
// 准备ApplicationContext
@Override
public void contextPrepared(ConfigurableApplicationContext context) {
this.initialMulticaster
.multicastEvent(new ApplicationContextInitializedEvent(this.application, this.args, context));
}
// 发布ApplicationContext已经refresh事件，标志着ApplicationContext初始化完成
@Override
public void contextLoaded(ConfigurableApplicationContext context) {
for (ApplicationListener<?> listener : this.application.getListeners()) {
if (listener instanceof ApplicationContextAware) {
((ApplicationContextAware) listener).setApplicationContext(context);
}
context.addApplicationListener(listener);
}
this.initialMulticaster.multicastEvent(new ApplicationPreparedEvent(this.application, this.args, context));
}
// SpringBoot已启动事件
@Override
public void started(ConfigurableApplicationContext context) {
context.publishEvent(new ApplicationStartedEvent(this.application, this.args, context));
AvailabilityChangeEvent.publish(context, LivenessState.CORRECT);
}
// "SpringBoot现在可以处理接受的请求"事件
@Override
public void running(ConfigurableApplicationContext context) {
context.publishEvent(new ApplicationReadyEvent(this.application, this.args, context));
AvailabilityChangeEvent.publish(context, ReadinessState.ACCEPTING_TRAFFIC);
}
@Override
public void failed(ConfigurableApplicationContext context, Throwable exception) {
ApplicationFailedEvent event = new ApplicationFailedEvent(this.application, this.args, context, exception);
if (context != null && context.isActive()) {
// Listeners have been registered to the application context so we should
// use it at this point if we can
context.publishEvent(event);
}
else {
// An inactive context may not have a multicaster so we use our multicaster to
// call all of the context‘s listeners instead
if (context instanceof AbstractApplicationContext) {
for (ApplicationListener<?> listener : ((AbstractApplicationContext) context)
.getApplicationListeners()) {
this.initialMulticaster.addApplicationListener(listener);
}
}
this.initialMulticaster.setErrorHandler(new LoggingErrorHandler());
this.initialMulticaster.multicastEvent(event);
}
}
private static class LoggingErrorHandler implements ErrorHandler {
private static final Log logger = LogFactory.getLog(EventPublishingRunListener.class);
@Override
public void handleError(Throwable throwable) {
logger.warn("Error calling ApplicationEventListener", throwable);
}
}
}
由于现在大都是用SpringBoot开发，所以呢，Spring IOC 初始化的源码，就是AnnotationConfigApplicationContext中的源码，IOC的初始化就是该类实例创建的过程。
创建的过程（AnnotationConfigApplicationContext的构造方法），由于debug过这个源码，我个人把它分为两大步（暂时我先写出我的总结，后续看是否有时间能写一篇关于debug的过程）：
SpringBoot启动原理（基于2.3.9.RELEASE版本）
标签：data inf hang getc map 配置 tca net dfa
原文地址：https://www.cnblogs.com/theRhyme/p/how-does-springboot-start.html
