SpringBoot源码 - 启动

public static ConfigurableApplicationContext run(Object[] sources, String[] args) {
  return new SpringApplication(sources).run(args);
}

private Class<?> deduceMainApplicationClass() {
  try {
  //获取线程栈数据
    StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
    for (StackTraceElement stackTraceElement : stackTrace) {
      if ("main".equals(stackTraceElement.getMethodName())) {
        return Class.forName(stackTraceElement.getClassName());
      }
    }
  }
  catch (ClassNotFoundException ex) {
    // Swallow and continue
  }
  return null;
}

public ConfigurableApplicationContext run(String... args) {
  StopWatch stopWatch = new StopWatch();
  stopWatch.start();
  ConfigurableApplicationContext context = null;
  //默认设置java.awt.headless为true
  configureHeadlessProperty(); 
  //从spring.factories中获取org.springframework.boot.SpringApplicationRunListener的实现类
  SpringApplicationRunListeners listeners = getRunListeners(args);
  //通过EventPublishingRunListener发布started事件
  listeners.started();
  try {
    ApplicationArguments applicationArguments = new DefaultApplicationArguments(
        args);
    //重点: 创建更新上下文对象
    context = createAndRefreshContext(listeners, applicationArguments);
    //上下文对象更新完调用
    afterRefresh(context, applicationArguments);
    //通过EventPublishingRunListener发布finished事件
    listeners.finished(context, null);
    stopWatch.stop();
    if (this.logStartupInfo) {
      new StartupInfoLogger(this.mainApplicationClass)
          .logStarted(getApplicationLog(), stopWatch);
    }
    return context;
  }
  catch (Throwable ex) {
    handleRunFailure(context, listeners, ex);
    throw new IllegalStateException(ex);
  }
}

public interface SpringApplicationRunListener {
void started();
void environmentPrepared(ConfigurableEnvironment environment);
void contextPrepared(ConfigurableApplicationContext context);
void contextLoaded(ConfigurableApplicationContext context);
void finished(ConfigurableApplicationContext context, Throwable exception);
}

private ConfigurableApplicationContext createAndRefreshContext(SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
  ConfigurableApplicationContext context;
  // Create and configure the environment
  //获取或创建环境实例, web环境使用StandardServletEnvironment, 非web环境使用StandardEnvironment
  ConfigurableEnvironment environment = getOrCreateEnvironment();
  //配置环境数据 
  //1. **commandLineArgs**属性从启动参数中解析, 格式"--name=value"
  //2. 配置profiles. 有效的profile(通过**spring.profiles.active**配置) 和 通过SpringApplication.profiles()指定的额外profile
  configureEnvironment(environment, applicationArguments.getSourceArgs());
  //通过EventPublishingRunListener发布environmentPrepared事件
  listeners.environmentPrepared(environment);
  //如果是web环境, 将非web环境实例转换成web环境实例: 
  //使用有效的profile配置和jndiProperties, servletConfigInitParams, servletContextInitParams的配置.
  if (isWebEnvironment(environment) && !this.webEnvironment) {
    environment = convertToStandardEnvironment(environment);
  }
  //输出banner
  if (this.bannerMode != Banner.Mode.OFF) {
    printBanner(environment);
  }

  //创建上下文对象, 没有指定实现类的话(使用SpringApplicationBuilder.contextClass), 使用默认context类. 然后通过反射实例化上下文对象.
  //1. web环境使用org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext
  //2. org.springframework.context.annotation.AnnotationConfigApplicationContext
  
  //初始化实例的时候会做很多事, 
  //1. 创建AnnotatedBeanDefinitionReader. 注册相关的Annotation Post Processor, 包括: ConfigurationClassPostProcessor(处理@Configuration标注的类), AutowiredAnnotationBeanPostProcessor, RequiredAnnotationBeanPostProcessor, CommonAnnotationBeanPostProcessor, PersistenceAnnotationBeanPostProcessor, EventListenerMethodProcessor, DefaultEventListenerFactory
  //2. 创建ClassPathBeanDefinitionScanner. 扫描器, 扫描默认的过滤器@Service, @Component, @Registry, @Controller. 同时支持J2EE6的@ManagedBean和@Named
  // Create, load, refresh and run the ApplicationContext
  context = createApplicationContext();
  //设置环境
  context.setEnvironment(environment);
  //后续的处理
  postProcessApplicationContext(context);
  //应用初始化器(ApplicationContextInitializer的实现类), 对上下文对象做更多初始化的操作, 比如: 
  //1. 添加BeanFactoryPostProcessor
  //2 .设置上下文对象id
  //3 .代理配置中context.initializer.classes指定的初始化类
  //4. 添加listener, 在web容器启动后更新环境变量中的端口号(server.ports中的local.server.port)
  applyInitializers(context);
  //通过EventPublishingRunListener发布contextPrepared事件
  listeners.contextPrepared(context);
  //打印启动信息和有效的profile信息
  if (this.logStartupInfo) {
    logStartupInfo(context.getParent() == null);
    logStartupProfileInfo(context);
  }

  //将ApplicationArguments实例注册到BeanFactory中, 名字为springApplicationArguments
  // Add boot specific singleton beans
  context.getBeanFactory().registerSingleton("springApplicationArguments",
      applicationArguments);

  //从source(可以是Resource, Package, CharSequence或者Class. 从run方法进来的为Class)类加载Bean到上下文对象中
  // Load the sources
  Set<Object> sources = getSources();
  Assert.notEmpty(sources, "Sources must not be empty");
  load(context, sources.toArray(new Object[sources.size()]));
  //通过EventPublishingRunListener发布contextLoaded事件
  listeners.contextLoaded(context);

  //更新上下文对象, 调用ApplicationContext.refresh()方法
  // Refresh the context
  refresh(context);
  if (this.registerShutdownHook) {
    try {
      context.registerShutdownHook();
    }
    catch (AccessControlException ex) {
      // Not allowed in some environments.
    }
  }
  return context;
}

@Configuration
@PropertySource("classpath:/com/acme/app.properties")
public class AppConfig {
    @Value("${bean.name}") String beanName;
    @Autowired DataSource dataSource;
    @Bean
    public MyBean myBean() {
        return new MyBean(beanName);
    }
    @Configuration
    @Profile("test")
    static class DatabaseConfigTest {
        @Bean
        DataSource dataSource() {
            return new EmbeddedDatabaseBuilder().build();
        }
    }
    @Configuration
    @Profile("production")
    static class DatabaseConfigProduction {
        @Bean
        DataSource dataSource() {
            return new EmbeddedDatabaseBuilder().build();
        }
    }
}