1. SpringBoot读取配置文件源码探究

1.1. 概览

• springboot的源码是再原来的Spring源码上又包了一层，看过spring源码都知道，当我们从入口debug进去的时候，原来的Spring源码都集中在refreshContext方法，SpringBoot的主要运行步骤，基本都包含在这个方法里了，而这个方法就是我们运行Springboot的主函数SpringApplication.run(Application.class, args);经过几步后到达的

	public ConfigurableApplicationContext run(String... args) {
		StopWatch stopWatch = new StopWatch();
		stopWatch.start();
		ConfigurableApplicationContext context = null;
		FailureAnalyzers analyzers = null;
		configureHeadlessProperty();
		SpringApplicationRunListeners listeners = getRunListeners(args);
		listeners.starting();
		try {
			ApplicationArguments applicationArguments = new DefaultApplicationArguments(
					args);
			ConfigurableEnvironment environment = prepareEnvironment(listeners,
					applicationArguments);
			Banner printedBanner = printBanner(environment);
			context = createApplicationContext();
			analyzers = new FailureAnalyzers(context);
			prepareContext(context, environment, listeners, applicationArguments,
					printedBanner);
			refreshContext(context);
			afterRefresh(context, applicationArguments);
			listeners.finished(context, null);
			stopWatch.stop();
			if (this.logStartupInfo) {
				new StartupInfoLogger(this.mainApplicationClass)
						.logStarted(getApplicationLog(), stopWatch);
			}
			return context;
		}
		catch (Throwable ex) {
			handleRunFailure(context, listeners, analyzers, ex);
			throw new IllegalStateException(ex);
		}
	}

1.2. 配置读取步骤

1.2.1. prepareEnvironment

• 配置读取的步骤主要就在ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);这一步，我们继续深入

	private ConfigurableEnvironment prepareEnvironment(
			SpringApplicationRunListeners listeners,
			ApplicationArguments applicationArguments) {
		// Create and configure the environment
		ConfigurableEnvironment environment = getOrCreateEnvironment();
		configureEnvironment(environment, applicationArguments.getSourceArgs());
		//主要是这步
		listeners.environmentPrepared(environment);
		if (!this.webEnvironment) {
			environment = new EnvironmentConverter(getClassLoader())
					.convertToStandardEnvironmentIfNecessary(environment);
		}
		return environment;
	}

• 创建基本的环境容器后，进入listeners.environmentPrepared(environment);通过监听器来进行环境变量的初始化，同时读取配置也是一部分工作

1.2.2. environmentPrepared

• 下一步，看到对监听器进行循环处理，这里的listeners中，默认只有一个EventPublishRunListener

	public void environmentPrepared(ConfigurableEnvironment environment) {
		for (SpringApplicationRunListener listener : this.listeners) {
			listener.environmentPrepared(environment);
		}
	}

• 继续如下，这一步它进行广播事件了

	@Override
	public void environmentPrepared(ConfigurableEnvironment environment) {
		this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(
				this.application, this.args, environment));
	}

1.2.3. multicastEvent

	@Override
	public void multicastEvent(ApplicationEvent event) {
		multicastEvent(event, resolveDefaultEventType(event));
	}

继续，重点是invokeListener方法，去调用监听器事件，可以想象对配置文件来讲，这就是读取配置事件了。同时监听器有很多，读取配置文件的监听器是ConfigFileAplicationListener，看名字还是蛮明显的吧

	@Override
	public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) {
		ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));
		for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {
			Executor executor = getTaskExecutor();
			if (executor != null) {
				executor.execute(new Runnable() {
					@Override
					public void run() {
						invokeListener(listener, event);
					}
				});
			}
			else {
				//重点
				invokeListener(listener, event);
			}
		}
	}

继续，和上一步类似，do真正的事件了

	protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {
		ErrorHandler errorHandler = getErrorHandler();
		if (errorHandler != null) {
			try {
				doInvokeListener(listener, event);
			}
			catch (Throwable err) {
				errorHandler.handleError(err);
			}
		}
		else {
			//重点
			doInvokeListener(listener, event);
		}
	}

	private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {
		try {
			// 入口
			listener.onApplicationEvent(event);
		}
		catch (ClassCastException ex) {
			String msg = ex.getMessage();
			if (msg == null || matchesClassCastMessage(msg, event.getClass())) {
				// Possibly a lambda-defined listener which we could not resolve the generic event type for
				// -> let\'s suppress the exception and just log a debug message.
				Log logger = LogFactory.getLog(getClass());
				if (logger.isDebugEnabled()) {
					logger.debug("Non-matching event type for listener: " + listener, ex);
				}
			}
			else {
				throw ex;
			}
		}
	}

1.2.4. onApplicationEvent

• 在ConfigFileApplicationListener类中继续

	@Override
	public void onApplicationEvent(ApplicationEvent event) {
		if (event instanceof ApplicationEnvironmentPreparedEvent) {
			//配置入口
			onApplicationEnvironmentPreparedEvent(
					(ApplicationEnvironmentPreparedEvent) event);
		}
		if (event instanceof ApplicationPreparedEvent) {
			onApplicationPreparedEvent(event);
		}
	}

继续，可以看到处理器有这些，我们关注ConfigFileApplicationListener

	private void onApplicationEnvironmentPreparedEvent(
			ApplicationEnvironmentPreparedEvent event) {
		List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
		postProcessors.add(this);
		AnnotationAwareOrderComparator.sort(postProcessors);
		for (EnvironmentPostProcessor postProcessor : postProcessors) {
			//入口
			postProcessor.postProcessEnvironment(event.getEnvironment(),
					event.getSpringApplication());
		}
	}

1.2.5. postProcessEnvironment

	@Override
	public void postProcessEnvironment(ConfigurableEnvironment environment,
			SpringApplication application) {
		//重点入口
		addPropertySources(environment, application.getResourceLoader());
		configureIgnoreBeanInfo(environment);
		bindToSpringApplication(environment, application);
	}

继续

	protected void addPropertySources(ConfigurableEnvironment environment,
			ResourceLoader resourceLoader) {
		RandomValuePropertySource.addToEnvironment(environment);
		//总算看到加载入口了
		new Loader(environment, resourceLoader).load();
	}

1.2.6. load

public void load() {
			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()) {
							//加载入口
							load(location, name, profile);
						}
					}
				}
				this.processedProfiles.add(profile);
			}

			addConfigurationProperties(this.propertiesLoader.getPropertySources());
		}

• 可以看到它的加载名从getSearchNames获取，那就看看这个方法

		private Set<String> getSearchNames() {
			if (this.environment.containsProperty(CONFIG_NAME_PROPERTY)) {
				return asResolvedSet(this.environment.getProperty(CONFIG_NAME_PROPERTY),
						null);
			}
			return asResolvedSet(ConfigFileApplicationListener.this.names, DEFAULT_NAMES);
		}

• CONFIG_NAME_PROPERTY值为spring.config.name，DEFAULT_NAMES值为application，所以可以看出application这个名字就是默认的配置名了，但也可以用spring.config.name属性来修改

• 其实到这一步，后面已经没难度了，可以想象，接下去应该是拼接出完整的路径，找到文件读取，还是走完流程把

• 继续

		private void load(String location, String name, Profile profile) {
			String group = "profile=" + ((profile != null) ? profile : "");
			if (!StringUtils.hasText(name)) {
				// Try to load directly from the location
				loadIntoGroup(group, location, profile);
			}
			else {
				// Search for a file with the given name
				for (String ext : this.propertiesLoader.getAllFileExtensions()) {
					if (profile != null) {
						// Try the profile-specific file
						loadIntoGroup(group, location + name + "-" + profile + "." + ext,
								null);
						for (Profile processedProfile : this.processedProfiles) {
							if (processedProfile != null) {
								loadIntoGroup(group, location + name + "-"
										+ processedProfile + "." + ext, profile);
							}
						}
						// Sometimes people put "spring.profiles: dev" in
						// application-dev.yml (gh-340). Arguably we should try and error
						// out on that, but we can be kind and load it anyway.
						loadIntoGroup(group, location + name + "-" + profile + "." + ext,
								profile);
					}
					// Also try the profile-specific section (if any) of the normal file
					//加载重点
					loadIntoGroup(group, location + name + "." + ext, profile);
				}
			}
		}

• 继续

		private PropertySource<?> loadIntoGroup(String identifier, String location,
				Profile profile) {
			try {
				//入口
				return doLoadIntoGroup(identifier, location, profile);
			}
			catch (Exception ex) {
				throw new IllegalStateException(
						"Failed to load property source from location \'" + location + "\'",
						ex);
			}
		}

• do开头都是正式要干事了

		private PropertySource<?> doLoadIntoGroup(String identifier, String location,
				Profile profile) throws IOException {
			Resource resource = this.resourceLoader.getResource(location);
			PropertySource<?> propertySource = null;
			StringBuilder msg = new StringBuilder();
			if (resource != null && resource.exists()) {
				String name = "applicationConfig: [" + location + "]";
				String group = "applicationConfig: [" + identifier + "]";
				// 加载入口
				propertySource = this.propertiesLoader.load(resource, group, name,
						(profile != null) ? profile.getName() : null);
				if (propertySource != null) {
					msg.append("Loaded ");
					handleProfileProperties(propertySource);
				}
				else {
					msg.append("Skipped (empty) ");
				}
			}
			else {
				msg.append("Skipped ");
			}
			msg.append("config file ");
			msg.append(getResourceDescription(location, resource));
			if (profile != null) {
				msg.append(" for profile ").append(profile);
			}
			if (resource == null || !resource.exists()) {
				msg.append(" resource not found");
				this.logger.trace(msg);
			}
			else {
				this.logger.debug(msg);
			}
			return propertySource;
		}

• load内容，这里有两个加载器，看名字也知道了，yml结尾的文件肯定用YamlPropertySourceLoader才能加载，properties结尾的用另一个
  

	public PropertySource<?> load(Resource resource, String group, String name,
			String profile) throws IOException {
		if (isFile(resource)) {
			String sourceName = generatePropertySourceName(name, profile);
			for (PropertySourceLoader loader : this.loaders) {
				if (canLoadFileExtension(loader, resource)) {
					// 干事的入口
					PropertySource<?> specific = loader.load(sourceName, resource,
							profile);
					addPropertySource(group, specific);
					return specific;
				}
			}
		}
		return null;
	}

• 我用的是yml，所以在YamlPropertySourceLoader类

	@Override
	public PropertySource<?> load(String name, Resource resource, String profile)
			throws IOException {
		if (ClassUtils.isPresent("org.yaml.snakeyaml.Yaml", null)) {
			Processor processor = new Processor(resource, profile);
			//真正的处理类
			Map<String, Object> source = processor.process();
			if (!source.isEmpty()) {
				return new MapPropertySource(name, source);
			}
		}
		return null;
	}

		public Map<String, Object> process() {
			final Map<String, Object> result = new LinkedHashMap<String, Object>();
			//接近了
			process(new MatchCallback() {
				@Override
				public void process(Properties properties, Map<String, Object> map) {
					result.putAll(getFlattenedMap(map));
				}
			});
			return result;
		}

1.2.7. process

	protected void process(MatchCallback callback) {
		Yaml yaml = createYaml();
		for (Resource resource : this.resources) {
			//更近了
			boolean found = process(callback, yaml, resource);
			if (this.resolutionMethod == ResolutionMethod.FIRST_FOUND && found) {
				return;
			}
		}
	}

• 继续深入
  
  
• 可以看到，总算把我配合文件的内容给读到了，然后放入callback

	private boolean process(MatchCallback callback, Yaml yaml, Resource resource) {
		int count = 0;
		try {
			if (logger.isDebugEnabled()) {
				logger.debug("Loading from YAML: " + resource);
			}
			//读取文件
			Reader reader = new UnicodeReader(resource.getInputStream());
			try {
				for (Object object : yaml.loadAll(reader)) {
					//总算拿到了
					if (object != null && process(asMap(object), callback)) {
						count++;
						if (this.resolutionMethod == ResolutionMethod.FIRST_FOUND) {
							break;
						}
					}
				}
				if (logger.isDebugEnabled()) {
					logger.debug("Loaded " + count + " document" + (count > 1 ? "s" : "") +
							" from YAML resource: " + resource);
				}
			}
			finally {
				reader.close();
			}
		}
		catch (IOException ex) {
			handleProcessError(resource, ex);
		}
		return (count > 0);
	}

• 结果就存入了result

• 这样之后返回去看，你就会看到它存入了MapPropertySource属性资源，在之后就会被用上了

1.3. 总结

• 我通过一步步的代码跟踪，解析了SpringBoot读取application.yml的整个流程，代码虽然贴的比较多，但可以让初学者也可以跟着这个步骤完整的理解一遍，代码中的关键步骤我都用中文标明了，其它没标注部分不是这章的重点，想研究的自行研究