public class InitApolloCluster implements ApplicationContextInitializer<ConfigurableApplicationContext>, Ordered {

    @Override
    public void initialize(ConfigurableApplicationContext applicationContext) {
        ConfigurableEnvironment environment = applicationContext.getEnvironment();
        String cluster = System.getProperty("apollo.cluster", environment.getProperty("apollo.cluster"));
        if(StringUtils.isNotBlank(cluster)){
            // 指定了cluster，不然使用default
            System.setProperty("apollo.cluster", cluster);
        }
    }

    @Override
    public int getOrder() {
		// 在封装的初始化类之后运行，其实没关系
        return Ordered.HIGHEST_PRECEDENCE + 2;
    }
}

org.springframework.context.ApplicationContextInitializer=XXXX...

protected void applyInitializers(ConfigurableApplicationContext context) {
	// 获取spring.factories配置的所有ApplicationContextInitializer实现类
	for (ApplicationContextInitializer initializer : getInitializers()) {
		Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(
				initializer.getClass(), ApplicationContextInitializer.class);
		Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
		initializer.initialize(context);
	}
}


// 路径从SpringApplication的run方法到prepareContext方法
public ConfigurableApplicationContext run(String... args) {
	// ...
	ConfigurableEnvironment environment = prepareEnvironment(listeners,
					applicationArguments);
	// ...
	// 准备上下文
	prepareContext(context, environment, listeners, applicationArguments,
					printedBanner);
	// ...
}

private void prepareContext(ConfigurableApplicationContext context,
			ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
			ApplicationArguments applicationArguments, Banner printedBanner) {
	context.setEnvironment(environment);
	postProcessApplicationContext(context);
	// 调用所有的初始化类
	applyInitializers(context);
	listeners.contextPrepared(context);
	// ...
}

public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
	ConfigurableEnvironment environment = event.getEnvironment();
	if (!environment.getProperty("spring.cloud.bootstrap.enabled", Boolean.class,
			true)) {
		return;
	}
	// don't listen to events in a bootstrap context
	if (environment.getPropertySources().contains(BOOTSTRAP_PROPERTY_SOURCE_NAME)) {
		return;
	}
	// 创建bootstrapServiceContext
	ConfigurableApplicationContext context = bootstrapServiceContext(environment,
			event.getSpringApplication());
	apply(context, event.getSpringApplication(), environment);
}

private ConfigurableApplicationContext bootstrapServiceContext(
		ConfigurableEnvironment environment, final SpringApplication application) {
	StandardEnvironment bootstrapEnvironment = new StandardEnvironment();
	MutablePropertySources bootstrapProperties = bootstrapEnvironment
			.getPropertySources();
	for (PropertySource<?> source : bootstrapProperties) {
		bootstrapProperties.remove(source.getName());
	}
	String configName = environment
			.resolvePlaceholders("${spring.cloud.bootstrap.name:bootstrap}");
	String configLocation = environment
			.resolvePlaceholders("${spring.cloud.bootstrap.location:}");
	Map<String, Object> bootstrapMap = new HashMap<>();
	bootstrapMap.put("spring.config.name", configName);
	if (StringUtils.hasText(configLocation)) {
		bootstrapMap.put("spring.config.location", configLocation);
	}
	bootstrapProperties.addFirst(
			new MapPropertySource(BOOTSTRAP_PROPERTY_SOURCE_NAME, bootstrapMap));
	for (PropertySource<?> source : environment.getPropertySources()) {
		bootstrapProperties.addLast(source);
	}
	ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
	// Use names and ensure unique to protect against duplicates
	List<String> names = SpringFactoriesLoader
			.loadFactoryNames(BootstrapConfiguration.class, classLoader);
	for (String name : StringUtils.commaDelimitedListToStringArray(
			environment.getProperty("spring.cloud.bootstrap.sources", ""))) {
		names.add(name);
	}
	// TODO: is it possible or sensible to share a ResourceLoader?
	// 这里创建了SpringApplicationBuilder
	SpringApplicationBuilder builder = new SpringApplicationBuilder()
			.profiles(environment.getActiveProfiles()).bannerMode(Mode.OFF)
			.environment(bootstrapEnvironment)
			.properties("spring.application.name:" + configName)
			.registerShutdownHook(false).logStartupInfo(false).web(false);
	List<Class<?>> sources = new ArrayList<>();
	for (String name : names) {
		Class<?> cls = ClassUtils.resolveClassName(name, null);
		try {
			cls.getDeclaredAnnotations();
		}
		catch (Exception e) {
			continue;
		}
		sources.add(cls);
	}
	builder.sources(sources.toArray(new Class[sources.size()]));
	AnnotationAwareOrderComparator.sort(sources);
	// 这里又调用了builder的run方法
	final ConfigurableApplicationContext context = builder.run();
	// Make the bootstrap context a parent of the app context
	addAncestorInitializer(application, context);
	// It only has properties in it now that we don't want in the parent so remove
	// it (and it will be added back later)
	bootstrapProperties.remove(BOOTSTRAP_PROPERTY_SOURCE_NAME);
	mergeDefaultProperties(environment.getPropertySources(), bootstrapProperties);
	return context;
}

public ConfigurableApplicationContext run(String... args) {
	if (this.running.get()) {
		// If already created we just return the existing context
		return this.context;
	}
	configureAsChildIfNecessary(args);
	if (this.running.compareAndSet(false, true)) {
		synchronized (this.running) {
			// If not already running copy the sources over and then run.
			this.context = build().run(args);
		}
	}
	return this.context;
}

public SpringApplication build() {
	return build(new String[0]);
}
public SpringApplication build(String... args) {
	configureAsChildIfNecessary(args);
	// 这里的application是在SpringApplicationBuilder创建时的构造函数中创建的
	// new SpringApplication(sources)
	this.application.setSources(this.sources);
	return this.application;
}

// 写在postProcessAfterInitialization中，即实现了BeanPostProcessor
ConfigService.getAppConfig().addChangeListener(new ConfigChangeListener() {
	@Override
	public void onChange(ConfigChangeEvent changeEvent) {
		Object oldSettings = springFactory.getBean(beanName);
		logger.info("before refresh {}", oldSettings.toString());
		refreshScope.refresh(beanName);
		Object newSettings = springFactory.getBean(beanName);
		logger.info("after refresh {}", newSettings.toString());
	}
});

@ManagedOperation(description = "Dispose of the current instance of bean name provided and force a refresh on next method execution.")
public boolean refresh(String name) {
	// 不以scopedTarget.开头，加上
	if (!name.startsWith(SCOPED_TARGET_PREFIX)) {
		// User wants to refresh the bean with this name but that isn't the one in the
		// cache...
		name = SCOPED_TARGET_PREFIX + name;
	}
	// Ensure lifecycle is finished if bean was disposable
	// 卸载类
	if (super.destroy(name)) {
		this.context.publishEvent(new RefreshScopeRefreshedEvent(name));
		return true;
	}
	return false;
}