SpringBoot配置檔案載入

1. ConfigFileApplicationListener類

1. 配置相關的屬性名基本都可以在這個類裡面找到. 例如 spring.profiles.active,application(配置檔案的名字；不過後綴名儲存在其他位置)等.
2. 另外該類的註釋已經解釋得比較清楚了.
3. 該類的載入位置是 spring-boot-1.5.7.RELEASE.jar下的META-INF/spring.factories中的 ApplicationListener, 而載入時機是構造SpringApplication例項時(參見本人部落格SpringBoot原始碼研究之Start
   中的第二節).

ConfigFileApplicationListener繼承鏈如下

1.1 實現了SmartApplicationListener介面

// ------- SmartApplicationListener介面實現
@Override
public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
	// 只支援`ApplicationEnvironmentPreparedEvent`和`ApplicationPreparedEvent`事件
	return ApplicationEnvironmentPreparedEvent.
 
class.isAssignableFrom(eventType)
			|| ApplicationPreparedEvent.class.isAssignableFrom(eventType);
}

@Override
public boolean supportsSourceType(Class<?> aClass) {
	// 支援所有的SourceType
	return true;
}
// -------- SmartApplicationListener介面的基介面ApplicationListener<ApplicationEvent>的實現
@Override
 

public void onApplicationEvent(ApplicationEvent event) {
	if (event instanceof ApplicationEnvironmentPreparedEvent) {
		onApplicationEnvironmentPreparedEvent(
				(ApplicationEnvironmentPreparedEvent) event);
	}
	if (event instanceof ApplicationPreparedEvent) {
		onApplicationPreparedEvent(event);
	}
}
// ApplicationEnvironmentPreparedEvent 型別事件 
private void onApplicationEnvironmentPreparedEvent(
		ApplicationEnvironmentPreparedEvent event) {
	List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
	// 將自身載入到集合中, 因為`ConfigFileApplicationListener`自身就實現了`EnvironmentPostProcessor`介面
	postProcessors.add(this);
	AnnotationAwareOrderComparator.sort(postProcessors);
	for (EnvironmentPostProcessor postProcessor : postProcessors) {
		postProcessor.postProcessEnvironment(event.getEnvironment(),
				event.getSpringApplication());
	}
}

List<EnvironmentPostProcessor> loadPostProcessors() {
	/* 從classpath下的每個jar中的"META-INF/spring.factories"中載入指定類, 例如這裡的條件下從spring-boot-1.5.7.RELEASE.jar中載入到的類如下:

# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor

	*/
	return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class,
			getClass().getClassLoader());
}

// ApplicationPreparedEvent 型別事件
private void onApplicationPreparedEvent(ApplicationEvent event) {
	this.logger.replayTo(ConfigFileApplicationListener.class);
	addPostProcessors(((ApplicationPreparedEvent) event).getApplicationContext());
}

/**
 * Add appropriate post-processors to post-configure the property-sources.
 * @param context the context to configure
 */
protected void addPostProcessors(ConfigurableApplicationContext context) {
	// 看PropertySourceOrderingPostProcessor名稱應該是對PropertySource進行排序
	// 注意PropertySourceOrderingPostProcessor實現了Ordered介面, 而且優先順序是最高的.
	context.addBeanFactoryPostProcessor(
			new PropertySourceOrderingPostProcessor(context));
}

1.2 實現了EnvironmentPostProcessor介面

@Override
public void postProcessEnvironment(ConfigurableEnvironment environment,
		SpringApplication application) {
	// RandomValuePropertySource就是在這裡被加入到environment中的
	// 配置檔案中可以通過`${random.xx}`來獲取隨機值. 相關的類就是這個`RandomValuePropertySource`.
	// 細節可以看看 RandomValuePropertySource實現的 getProperty方法
	addPropertySources(environment, application.getResourceLoader());
	configureIgnoreBeanInfo(environment);
	bindToSpringApplication(environment, application);
}
// Add config file property sources to the specified environment.
protected void addPropertySources(ConfigurableEnvironment environment,
		ResourceLoader resourceLoader) {
	RandomValuePropertySource.addToEnvironment(environment);
	// 就是在這裡將配置檔案進行載入
	new Loader(environment, resourceLoader).load();
}

2. 時機

在繼續深入ConfigFileApplicationListener.Loader之前, 讓我們回頭看看Spring是如何執行到這裡的, 如下圖堆疊所示

private ConfigurableEnvironment prepareEnvironment(
		SpringApplicationRunListeners listeners,
		ApplicationArguments applicationArguments) {
	// 這裡的引數listeners的來源:
	// spring-boot-1.5.7.RELEASE.jar中的"META-INF/spring.factories"中的SpringApplicationRunListener實現.

	// Create and configure the environment
	// 這裡的getOrCreateEnvironment()方法會建立一個StandardServletEnvironment例項(web環境下,如何判斷請參考之前的文章).
	ConfigurableEnvironment environment = getOrCreateEnvironment();
	// 根據使用者傳入的引數對environment進行配置.
	configureEnvironment(environment, applicationArguments.getSourceArgs());
	// 觸發ApplicationEnvironmentPreparedEvent事件. 這也和上面的邏輯吻合上了.
	listeners.environmentPrepared(environment);
	if (!this.webEnvironment) {
	// 優秀的原始碼讀到一定的量之後, 應該就會有這樣一個感受: 
	// 它們很少將功能集中在一起, 而是進行拆分為一個個小的功能點;
	// 這也是新手在閱讀原始碼時會碰到比較大的問題之一, 跟著跳來跳去就暈了.
	// 這裡也是一樣, 當發現當前不是web環境時, 就委託給一個專門的類去處理轉換當前的environment. 這裡使用的類名和方法名已經很清楚地表明瞭所做的事情.
		environment = new EnvironmentConverter(getClassLoader())
				.convertToStandardEnvironmentIfNecessary(environment);
	}
	return environment;
}

3. ConfigFileApplicationListener.Loader類

作為ConfigFileApplicationListener類的內部類, Loader負責對配置檔案進行載入.

public void load() {
	/* 這裡的PropertySourcesLoader會從`spring-boot-1.5.7.RELEASE.jar`下的`META-INF/spring.factories`中載入
	
# PropertySource Loaders 屬性檔案載入
org.springframework.boot.env.PropertySourceLoader=\
org.springframework.boot.env.PropertiesPropertySourceLoader,\
org.springframework.boot.env.YamlPropertySourceLoader	
	*/
	this.propertiesLoader = new PropertySourcesLoader();
	this.activatedProfiles = false;
	this.profiles = Collections.asLifoQueue(new LinkedList<Profile>());
	this.processedProfiles = new LinkedList<Profile>();

	// Pre-existing active profiles set via Environment.setActiveProfiles()
	// are additional profiles and config files are allowed to add more if
	// they want to, so don't call addActiveProfiles() here.
	Set<Profile> initialActiveProfiles = initializeActiveProfiles();
	this.profiles.addAll(getUnprocessedActiveProfiles(initialActiveProfiles));
	if (this.profiles.isEmpty()) {
		for (String defaultProfileName : this.environment.getDefaultProfiles()) {
			Profile defaultProfile = new Profile(defaultProfileName, true);
			if (!this.profiles.contains(defaultProfile)) {
				this.profiles.add(defaultProfile);
			}
		}
	}

	// The default profile for these purposes is represented as null. We add it
	// last so that it is first out of the queue (active profiles will then
	// override any settings in the defaults when the list is reversed later).
	this.profiles.add(null);

	while (!this.profiles.isEmpty()) {
		Profile profile = this.profiles.poll();
		for (String location : getSearchLocations()) {
			if (!location.endsWith("/")) {
				// location is a filename already, so don't search for more
				// filenames
				load(location, null, profile);
			}
			else {
				for (String name : getSearchNames()) {
					load(location, name, profile);
				}
			}
		}
		this.processedProfiles.add(profile);
	}
	
	// 將解析過後的資源資訊放置進Enviroment中propertySources屬性集合中
	addConfigurationProperties(this.propertiesLoader.getPropertySources());
}

5. 亮點

1. ConfigFileApplicationListener類同時實現了EnvironmentPostProcessor介面和SmartApplicationListener介面，而在監聽回撥中又呼叫所有EnvironmentPostProcessor介面實現類， 這樣就將配置檔案的解析工作從主流程中剝離出來了，但其實又是集中在一個類裡面的。
2. ConfigFileApplicationListener類中的內部類Loader類專職了配置檔案的解析和載入工作，這樣ConfigFileApplicationListener類的職責就更加單一了。

6. 總結

1. ConfigFileApplicationListener類的例項通過spring-boot-1.5.7.RELEASE.jar下的META-INF/spring.factories配置檔案載入進容器。
2. ConfigFileApplicationListener類通過監聽ApplicationEnvironmentPreparedEvent事件來進行自定義配置檔案的讀取。

7. Links