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1.使用getEnvironment()获取环境信息

ApplicationContext接口继承了EnvironmentCapable接口，可以通过getEnvironment()获取Environment配置信息，例如：

@SpringBootApplication
public class A01 {public static void main(String[] args) throws IOException {ConfigurableApplicationContext context = SpringApplication.run(A01.class, args);// 获取系统配置及自定义配置信息System.out.println(context.getEnvironment().getProperty("java_home"));System.out.println(context.getEnvironment().getProperty("server.port"));}
}

接下来我们就探究下SpringBoot是如何加载环境及配置信息的

2.Spring读取环境信息原理

2.1 创建Environment对象

SpringBoot启动时就会调用prepareEnvironment创建Environment对象，SpringApplication#run源码如下：

public ConfigurableApplicationContext run(String... args) {// 省略其他代码...// 创建Environment对象，其中包括系统环境信息及Spring配置文件信息ConfigurableEnvironment environment = prepareEnvironment(listeners, bootstrapContext, applicationArguments);configureIgnoreBeanInfo(environment);Banner printedBanner = printBanner(environment);context = createApplicationContext();context.setApplicationStartup(this.applicationStartup);// 将一些对象设置到容器中，其中包含Environment对象prepareContext(bootstrapContext, context, environment, listeners, applicationArguments, printedBanner);refreshContext(context);afterRefresh(context, applicationArguments);// 省略其他代码...return context;
}

进入prepareEnvironment方法中创建Environment对象的源码如下：

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) {// 1.创建ConfigurableEnvironment对象ConfigurableEnvironment environment = this.getOrCreateEnvironment();// 补充启动参数this.configureEnvironment(environment, applicationArguments.getSourceArgs());// 创建ConfigurationPropertySourcesConfigurationPropertySources.attach(environment);// 2.通过发送事件的方式加载Spring配置listeners.environmentPrepared(bootstrapContext, environment);// 将DefaultPropertiesPropertySource移动到数组尾部DefaultPropertiesPropertySource.moveToEnd(environment);Assert.state(!environment.containsProperty("spring.main.environment-prefix"), "Environment prefix cannot be set via properties.");this.bindToSpringApplication(environment);if (!this.isCustomEnvironment) {EnvironmentConverter environmentConverter = new EnvironmentConverter(this.getClassLoader());environment = environmentConverter.convertEnvironmentIfNecessary(environment, this.deduceEnvironmentClass());}// 更新ConfigurationPropertySourcesConfigurationPropertySources.attach(environment);return environment;
}

创建ConfigurableEnvironment对象源码如下：

private ConfigurableEnvironment getOrCreateEnvironment() {// 此时environment为nullif (this.environment != null) {return this.environment;} else {// 调用DefaultApplicationContextFactory创建environmentConfigurableEnvironment environment = this.applicationContextFactory.createEnvironment(this.webApplicationType);if (environment == null && this.applicationContextFactory != ApplicationContextFactory.DEFAULT) {environment = ApplicationContextFactory.DEFAULT.createEnvironment(this.webApplicationType);}return (ConfigurableEnvironment)(environment != null ? environment : new ApplicationEnvironment());}
}// DefaultApplicationContextFactory#createEnvironment
public ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {// 调用静态方法引用ApplicationContextFactory::createEnvironment创建environmentreturn (ConfigurableEnvironment)this.getFromSpringFactories(webApplicationType, ApplicationContextFactory::createEnvironment, (Supplier)null);
}private <T> T getFromSpringFactories(WebApplicationType webApplicationType, BiFunction<ApplicationContextFactory, WebApplicationType, T> action, Supplier<T> defaultResult) {Iterator var4 = SpringFactoriesLoader.loadFactories(ApplicationContextFactory.class, this.getClass().getClassLoader()).iterator();Object result;do {if (!var4.hasNext()) {return defaultResult != null ? defaultResult.get() : null;}ApplicationContextFactory candidate = (ApplicationContextFactory)var4.next();// 创建environment，实际调用的是Factory#createEnvironmentresult = action.apply(candidate, webApplicationType);} while(result == null);return result;
}

这里的静态方法引用调用的是AnnotationConfigServletWebServerApplicationContext.Factory#createEnvironment，创建的对象是ApplicationServletEnvironment的实例

public ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {return webApplicationType != WebApplicationType.SERVLET ? null : new ApplicationServletEnvironment();
}

2.2 读取系统配置

ApplicationServletEnvironment创建实例时会调用父类AbstractEnvironment的构造函数初始化环境信息

public AbstractEnvironment() {this(new MutablePropertySources());
}protected AbstractEnvironment(MutablePropertySources propertySources) {this.logger = LogFactory.getLog(this.getClass());this.activeProfiles = new LinkedHashSet();this.defaultProfiles = new LinkedHashSet(this.getReservedDefaultProfiles());this.propertySources = propertySources;this.propertyResolver = this.createPropertyResolver(propertySources);// 会调用到StandardEnvironment#customizePropertySources加载系统配置this.customizePropertySources(propertySources);
}

调用子类的StandardEnvironment#customizePropertySources加载系统配置

protected void customizePropertySources(MutablePropertySources propertySources) {// 读取系统配置propertySources.addLast(new PropertiesPropertySource("systemProperties", this.getSystemProperties()));// 读取系统信息propertySources.addLast(new SystemEnvironmentPropertySource("systemEnvironment", this.getSystemEnvironment()));
}// AbstractEnvironment#getSystemProperties
public Map<String, Object> getSystemProperties() {try {// 获取系统配置return System.getProperties();} catch (AccessControlException var2) {return new ReadOnlySystemAttributesMap() {@Nullableprotected String getSystemAttribute(String attributeName) {try {return System.getProperty(attributeName);} catch (AccessControlException var3) {if (AbstractEnvironment.this.logger.isInfoEnabled()) {AbstractEnvironment.this.logger.info("Caught AccessControlException when accessing system property '" + attributeName + "'; its value will be returned [null]. Reason: " + var3.getMessage());}return null;}}};}
}// AbstractEnvironment#getSystemEnvironment
public Map<String, Object> getSystemEnvironment() {if (this.suppressGetenvAccess()) {return Collections.emptyMap();} else {try {// 读取环境信息return System.getenv();} catch (AccessControlException var2) {return new ReadOnlySystemAttributesMap() {@Nullableprotected String getSystemAttribute(String attributeName) {try {return System.getenv(attributeName);} catch (AccessControlException var3) {if (AbstractEnvironment.this.logger.isInfoEnabled()) {AbstractEnvironment.this.logger.info("Caught AccessControlException when accessing system environment variable '" + attributeName + "'; its value will be returned [null]. Reason: " + var3.getMessage());}return null;}}};}}
}

到这一步，系统的环境信息就获取到了，例如java.home、os.version等，那么Spring配置文件application.properties等配置信息怎么获取的呢？

2.3 加载Spring配置

2.3.1 发布事件

加载Spring配置是通过调用listeners.environmentPrepared(bootstrapContext, environment)发布ApplicationEnvironmentPreparedEvent事件来完成的，具体看源码SpringApplicationRunListeners#environmentPrepared

void environmentPrepared(ConfigurableBootstrapContext bootstrapContext, ConfigurableEnvironment environment) {this.doWithListeners("spring.boot.application.environment-prepared", (listener) -> {listener.environmentPrepared(bootstrapContext, environment);});
}private void doWithListeners(String stepName, Consumer<SpringApplicationRunListener> listenerAction) {this.doWithListeners(stepName, listenerAction, (Consumer)null);
}private void doWithListeners(String stepName, Consumer<SpringApplicationRunListener> listenerAction, Consumer<StartupStep> stepAction) {StartupStep step = this.applicationStartup.start(stepName);// 调用消费者发布事件this.listeners.forEach(listenerAction);if (stepAction != null) {stepAction.accept(step);}step.end();
}

doWithListeners中会调用listener.environmentPrepared(bootstrapContext, environment)发布事件，源码见EventPublishingRunListener#environmentPrepared

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

可见发布的事件类型是ApplicationEnvironmentPreparedEvent，进入multicastEvent方法

public void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));Executor executor = getTaskExecutor();for (ApplicationListener<?> listener : getApplicationListeners(event, type)) {if (executor != null) {executor.execute(() -> invokeListener(listener, event));}else {// 调用监听器处理事件invokeListener(listener, event);}}
}protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {ErrorHandler errorHandler = getErrorHandler();if (errorHandler != null) {try {doInvokeListener(listener, event);}catch (Throwable err) {errorHandler.handleError(err);}}else {doInvokeListener(listener, event);}
}@SuppressWarnings({"rawtypes", "unchecked"})
private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {try {listener.onApplicationEvent(event);}// 省略异常处理代码...
}

最终调用ApplicationListener的onApplicationEvent方法处理事件的

2.3.2 注册事件处理器

这里我们可能疑惑，这些事件处理器是怎么注册的呢？

首先SpringBoot项目启动时，会调用SpringApplication构造器设置listeners

public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {this.resourceLoader = resourceLoader;Assert.notNull(primarySources, "PrimarySources must not be null");this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));this.webApplicationType = WebApplicationType.deduceFromClasspath();this.bootstrapRegistryInitializers = new ArrayList<>(getSpringFactoriesInstances(BootstrapRegistryInitializer.class));setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));// 设置ApplicationListenersetListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));this.mainApplicationClass = deduceMainApplicationClass();
}

进入getSpringFactoriesInstances(ApplicationListener.class)方法内部

private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {return getSpringFactoriesInstances(type, new Class<?>[] {});
}private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {ClassLoader classLoader = getClassLoader();// 从配置文件中获取listener类名Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));// 实例化List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);AnnotationAwareOrderComparator.sort(instances);return instances;
}

通过读取spring.factories配置文件获取listener类名，然后实例化对象

public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {ClassLoader classLoaderToUse = classLoader;if (classLoaderToUse == null) {classLoaderToUse = SpringFactoriesLoader.class.getClassLoader();}String factoryTypeName = factoryType.getName();return loadSpringFactories(classLoaderToUse).getOrDefault(factoryTypeName, Collections.emptyList());
}private static Map<String, List<String>> loadSpringFactories(ClassLoader classLoader) {Map<String, List<String>> result = cache.get(classLoader);if (result != null) {return result;}result = new HashMap<>();try {// 获取META-INF/spring.factories资源文件URLEnumeration<URL> urls = classLoader.getResources(FACTORIES_RESOURCE_LOCATION);while (urls.hasMoreElements()) {URL url = urls.nextElement();UrlResource resource = new UrlResource(url);// 读取配置文件中的值Properties properties = PropertiesLoaderUtils.loadProperties(resource);for (Map.Entry<?, ?> entry : properties.entrySet()) {String factoryTypeName = ((String) entry.getKey()).trim();String[] factoryImplementationNames =StringUtils.commaDelimitedListToStringArray((String) entry.getValue());for (String factoryImplementationName : factoryImplementationNames) {result.computeIfAbsent(factoryTypeName, key -> new ArrayList<>()).add(factoryImplementationName.trim());}}}result.replaceAll((factoryType, implementations) -> implementations.stream().distinct().collect(Collectors.collectingAndThen(Collectors.toList(), Collections::unmodifiableList)));cache.put(classLoader, result);}catch (IOException ex) {throw new IllegalArgumentException("Unable to load factories from location [" +FACTORIES_RESOURCE_LOCATION + "]", ex);}return result;
}

spring-boot的jar包中的META-INF/spring.factories配置如下：

# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.env.EnvironmentPostProcessorApplicationListener

所以EnvironmentPostProcessorApplicationListener会被添加到容器中

当调用SpringApplication.run时，EventPublishingRunListener也会被创建，源码如下：

public ConfigurableApplicationContext run(String... args) {// 省略其他代码...// 创建EventPublishingRunListenerSpringApplicationRunListeners listeners = getRunListeners(args);// 省略其他代码...
}private SpringApplicationRunListeners getRunListeners(String[] args) {Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };return new SpringApplicationRunListeners(logger,getSpringFactoriesInstances(SpringApplicationRunListener.class, types, this, args),this.applicationStartup);
}private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {return getSpringFactoriesInstances(type, new Class<?>[] {});
}private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {ClassLoader classLoader = getClassLoader();// 从配置文件中获取SpringApplicationRunListener的类名Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader));// 实例化对象List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);AnnotationAwareOrderComparator.sort(instances);return instances;
}

spring-boot的jar包中的META-INF/spring.factories配置如下：

# Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
org.springframework.boot.context.event.EventPublishingRunListener

所以EventPublishingRunListener对象会被创建，源码如下：

public EventPublishingRunListener(SpringApplication application, String[] args) {this.application = application;this.args = args;this.initialMulticaster = new SimpleApplicationEventMulticaster();// 添加ApplicationListener到initialMulticaster中for (ApplicationListener<?> listener : application.getListeners()) {this.initialMulticaster.addApplicationListener(listener);}
}

application.getListeners()会获取到上文中添加到容器中的listeners，将每个listener添加到initialMulticaster中，源码如下：

public void addApplicationListener(ApplicationListener<?> listener) {synchronized (this.defaultRetriever) {Object singletonTarget = AopProxyUtils.getSingletonTarget(listener);if (singletonTarget instanceof ApplicationListener) {this.defaultRetriever.applicationListeners.remove(singletonTarget);}// 添加到defaultRetriever的applicationListeners成员变量中this.defaultRetriever.applicationListeners.add(listener);this.retrieverCache.clear();}
}

这样defaultRetriever的applicationListeners成员变量就保存了这些listener对象

再看看multicastEvent方法中的getApplicationListeners(event, type)，会调用retrieveApplicationListeners

private Collection<ApplicationListener<?>> retrieveApplicationListeners(ResolvableType eventType, @Nullable Class<?> sourceType, @Nullable CachedListenerRetriever retriever) {List<ApplicationListener<?>> allListeners = new ArrayList<>();Set<ApplicationListener<?>> filteredListeners = (retriever != null ? new LinkedHashSet<>() : null);Set<String> filteredListenerBeans = (retriever != null ? new LinkedHashSet<>() : null);Set<ApplicationListener<?>> listeners;Set<String> listenerBeans;synchronized (this.defaultRetriever) {// 从defaultRetriever中获取listenerslisteners = new LinkedHashSet<>(this.defaultRetriever.applicationListeners);listenerBeans = new LinkedHashSet<>(this.defaultRetriever.applicationListenerBeans);}// 过滤符合条件的listenerfor (ApplicationListener<?> listener : listeners) {if (supportsEvent(listener, eventType, sourceType)) {if (retriever != null) {filteredListeners.add(listener);}allListeners.add(listener);}}// 省略部分代码...return allListeners;
}

这样就获取到了listener处理事件，其中就包括EnvironmentPostProcessorApplicationListener

2.3.3 处理事件

EnvironmentPostProcessorApplicationListener#onApplicationEvent会处理上述发布的ApplicationEnvironmentPreparedEvent事件

public void onApplicationEvent(ApplicationEvent event) {if (event instanceof ApplicationEnvironmentPreparedEvent) {// 处理ApplicationEnvironmentPreparedEvent事件this.onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent)event);}if (event instanceof ApplicationPreparedEvent) {this.onApplicationPreparedEvent();}if (event instanceof ApplicationFailedEvent) {this.onApplicationFailedEvent();}
}private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {ConfigurableEnvironment environment = event.getEnvironment();SpringApplication application = event.getSpringApplication();// 获取环境相关的后处理器for (EnvironmentPostProcessor postProcessor : getEnvironmentPostProcessors(application.getResourceLoader(),event.getBootstrapContext())) {postProcessor.postProcessEnvironment(environment, application);}
}

getEnvironmentPostProcessors会读取spring.factories配置文件获取EnvironmentPostProcessor

List<EnvironmentPostProcessor> getEnvironmentPostProcessors(ResourceLoader resourceLoader,ConfigurableBootstrapContext bootstrapContext) {ClassLoader classLoader = (resourceLoader != null) ? resourceLoader.getClassLoader() : null;// 这个postProcessorsFactory是通过构造器添加的EnvironmentPostProcessorsFactory postProcessorsFactory = this.postProcessorsFactory.apply(classLoader);return postProcessorsFactory.getEnvironmentPostProcessors(this.deferredLogs, bootstrapContext);
}

this.postProcessorsFactory.apply(classLoader)会调用如下EnvironmentPostProcessorsFactory#fromSpringFactories，加载EnvironmentPostProcessor

static EnvironmentPostProcessorsFactory fromSpringFactories(ClassLoader classLoader) {return new ReflectionEnvironmentPostProcessorsFactory(classLoader,SpringFactoriesLoader.loadFactoryNames(EnvironmentPostProcessor.class, classLoader));
}

spring-boot的jar包中的META-INF/spring.factories配置如下：

# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
org.springframework.boot.context.config.ConfigDataEnvironmentPostProcessor,\
org.springframework.boot.env.RandomValuePropertySourceEnvironmentPostProcessor,\
org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\
org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor,\
org.springframework.boot.reactor.DebugAgentEnvironmentPostProcessor

getEnvironmentPostProcessors就会实例化EnvironmentPostProcessor，这样ConfigDataEnvironmentPostProcessor对象就会被创建，调用它的postProcessEnvironment时获取配置信息

void postProcessEnvironment(ConfigurableEnvironment environment, ResourceLoader resourceLoader,Collection<String> additionalProfiles) {try {this.logger.trace("Post-processing environment to add config data");resourceLoader = (resourceLoader != null) ? resourceLoader : new DefaultResourceLoader();// 创建ConfigDataEnvironment获取配置信息getConfigDataEnvironment(environment, resourceLoader, additionalProfiles).processAndApply();}catch (UseLegacyConfigProcessingException ex) {this.logger.debug(LogMessage.format("Switching to legacy config file processing [%s]",ex.getConfigurationProperty()));configureAdditionalProfiles(environment, additionalProfiles);postProcessUsingLegacyApplicationListener(environment, resourceLoader);}
}ConfigDataEnvironment getConfigDataEnvironment(ConfigurableEnvironment environment, ResourceLoader resourceLoader,Collection<String> additionalProfiles) {return new ConfigDataEnvironment(this.logFactory, this.bootstrapContext, environment, resourceLoader,additionalProfiles, this.environmentUpdateListener);
}

ConfigDataEnvironment是SpringBoot配置数据加载和管理的核心组件，它的构造函数如下，主要创建了ConfigDataLocationResolvers、ConfigDataLoaders及ConfigDataEnvironmentContributors

ConfigDataEnvironment(DeferredLogFactory logFactory, ConfigurableBootstrapContext bootstrapContext,ConfigurableEnvironment environment, ResourceLoader resourceLoader, Collection<String> additionalProfiles,ConfigDataEnvironmentUpdateListener environmentUpdateListener) {Binder binder = Binder.get(environment);UseLegacyConfigProcessingException.throwIfRequested(binder);this.logFactory = logFactory;this.logger = logFactory.getLog(getClass());this.notFoundAction = binder.bind(ON_NOT_FOUND_PROPERTY, ConfigDataNotFoundAction.class).orElse(ConfigDataNotFoundAction.FAIL);this.bootstrapContext = bootstrapContext;this.environment = environment;// 创建配置文件位置解析器this.resolvers = createConfigDataLocationResolvers(logFactory, bootstrapContext, binder, resourceLoader);this.additionalProfiles = additionalProfiles;this.environmentUpdateListener = (environmentUpdateListener != null) ? environmentUpdateListener: ConfigDataEnvironmentUpdateListener.NONE;// 创建配置文件加载器this.loaders = new ConfigDataLoaders(logFactory, bootstrapContext, resourceLoader.getClassLoader());// 创建ConfigDataEnvironmentContributorsthis.contributors = createContributors(binder);
}// ConfigDataLocationResolvers构造器
ConfigDataLocationResolvers(DeferredLogFactory logFactory, ConfigurableBootstrapContext bootstrapContext,Binder binder, ResourceLoader resourceLoader) {this(logFactory, bootstrapContext, binder, resourceLoader, SpringFactoriesLoader.loadFactoryNames(ConfigDataLocationResolver.class, resourceLoader.getClassLoader()));
}// ConfigDataLoaders构造器
ConfigDataLoaders(DeferredLogFactory logFactory, ConfigurableBootstrapContext bootstrapContext,ClassLoader classLoader) {this(logFactory, bootstrapContext, classLoader,SpringFactoriesLoader.loadFactoryNames(ConfigDataLoader.class, classLoader));
}

这里也通过SpringFactoriesLoader#loadFactoryNames从配置文件中创建ConfigDataLocationResolver及ConfigDataLoader的，spring-boot的jar包中的META-INF/spring.factories配置如下：

# ConfigData Location Resolvers
org.springframework.boot.context.config.ConfigDataLocationResolver=\
org.springframework.boot.context.config.ConfigTreeConfigDataLocationResolver,\
org.springframework.boot.context.config.StandardConfigDataLocationResolver# ConfigData Loaders
org.springframework.boot.context.config.ConfigDataLoader=\
org.springframework.boot.context.config.ConfigTreeConfigDataLoader,\
org.springframework.boot.context.config.StandardConfigDataLoader

其中StandardConfigDataLocationResolver用于解析标准的配置文件位置，例如类路径下的config目录中的applicaiton.properties或者applicaiton.yml，而StandardConfigDataLoader则用于加载标准的配置数据

创建ConfigDataEnvironmentContributors源码如下：

private ConfigDataEnvironmentContributors createContributors(Binder binder) {this.logger.trace("Building config data environment contributors");MutablePropertySources propertySources = this.environment.getPropertySources();List<ConfigDataEnvironmentContributor> contributors = new ArrayList<>(propertySources.size() + 10);PropertySource<?> defaultPropertySource = null;for (PropertySource<?> propertySource : propertySources) {if (DefaultPropertiesPropertySource.hasMatchingName(propertySource)) {defaultPropertySource = propertySource;}else {this.logger.trace(LogMessage.format("Creating wrapped config data contributor for '%s'",propertySource.getName()));contributors.add(ConfigDataEnvironmentContributor.ofExisting(propertySource));}}// 关键方法：getInitialImportContributorscontributors.addAll(getInitialImportContributors(binder));if (defaultPropertySource != null) {this.logger.trace("Creating wrapped config data contributor for default property source");contributors.add(ConfigDataEnvironmentContributor.ofExisting(defaultPropertySource));}return createContributors(contributors);
}protected ConfigDataEnvironmentContributors createContributors(List<ConfigDataEnvironmentContributor> contributors) {return new ConfigDataEnvironmentContributors(this.logFactory, this.bootstrapContext, contributors);
}

ConfigDataEnvironmentContributors主要作用是维护一组ConfigDataEnvironmentContributor，而每个ConfigDataEnvironmentContributor用于配置数据的加载、处理和管理

这里重点看下getInitialImportContributors(binder)获取初始导入的ConfigDataEnvironmentContributor，这决定了配置文件的加载位置及顺序

private List<ConfigDataEnvironmentContributor> getInitialImportContributors(Binder binder) {List<ConfigDataEnvironmentContributor> initialContributors = new ArrayList<>();// 1.指定spring.config.import要导入的额外配置文件位置addInitialImportContributors(initialContributors, bindLocations(binder, IMPORT_PROPERTY, EMPTY_LOCATIONS));// 2.指定spring.config.additional-location额外的配置文件位置addInitialImportContributors(initialContributors,bindLocations(binder, ADDITIONAL_LOCATION_PROPERTY, EMPTY_LOCATIONS));// 3.指定spring.config.location默认配置文件位置addInitialImportContributors(initialContributors,bindLocations(binder, LOCATION_PROPERTY, DEFAULT_SEARCH_LOCATIONS));return initialContributors;
}private void addInitialImportContributors(List<ConfigDataEnvironmentContributor> initialContributors,ConfigDataLocation[] locations) {// 从后往前遍历for (int i = locations.length - 1; i >= 0; i--) {initialContributors.add(createInitialImportContributor(locations[i]));}
}

在第3步中指定的配置文件地址DEFAULT_SEARCH_LOCATIONS包含：

static final ConfigDataLocation[] DEFAULT_SEARCH_LOCATIONS;
static {List<ConfigDataLocation> locations = new ArrayList<>();locations.add(ConfigDataLocation.of("optional:classpath:/;optional:classpath:/config/"));locations.add(ConfigDataLocation.of("optional:file:./;optional:file:./config/;optional:file:./config/*/"));DEFAULT_SEARCH_LOCATIONS = locations.toArray(new ConfigDataLocation[0]);
}

而addInitialImportContributors是从后往前遍历的，因此加载顺序为：

file:./
file:./config/
file:./config/*/
classpath:/
classpath:/config/

创建ConfigDataEnvironmentContributors完成后就会调用ConfigDataEnvironment#processAndApply加载和解析配置文件，源码如下：

void processAndApply() {// 创建数据导入器ConfigDataImporter importer = new ConfigDataImporter(this.logFactory, this.notFoundAction, this.resolvers,this.loaders);registerBootstrapBinder(this.contributors, null, DENY_INACTIVE_BINDING);// 执行加载以及解析初始的配置文件ConfigDataEnvironmentContributors contributors = processInitial(this.contributors, importer);// 处理profiles相关的配置，包括云平台配置及本地环境配置ConfigDataActivationContext activationContext = createActivationContext(contributors.getBinder(null, BinderOption.FAIL_ON_BIND_TO_INACTIVE_SOURCE));contributors = processWithoutProfiles(contributors, importer, activationContext);activationContext = withProfiles(contributors, activationContext);contributors = processWithProfiles(contributors, importer, activationContext);// 将配置数据添加到环境对象中applyToEnvironment(contributors, activationContext, importer.getLoadedLocations(),importer.getOptionalLocations());
}private ConfigDataEnvironmentContributors processInitial(ConfigDataEnvironmentContributors contributors,ConfigDataImporter importer) {this.logger.trace("Processing initial config data environment contributors without activation context");// 调用ConfigDataEnvironmentContributors加载配置contributors = contributors.withProcessedImports(importer, null);registerBootstrapBinder(contributors, null, DENY_INACTIVE_BINDING);return contributors;
}private ConfigDataEnvironmentContributors processWithoutProfiles(ConfigDataEnvironmentContributors contributors,ConfigDataImporter importer, ConfigDataActivationContext activationContext) {this.logger.trace("Processing config data environment contributors with initial activation context");contributors = contributors.withProcessedImports(importer, activationContext);registerBootstrapBinder(contributors, activationContext, DENY_INACTIVE_BINDING);return contributors;
}private ConfigDataEnvironmentContributors processWithProfiles(ConfigDataEnvironmentContributors contributors,ConfigDataImporter importer, ConfigDataActivationContext activationContext) {this.logger.trace("Processing config data environment contributors with profile activation context");contributors = contributors.withProcessedImports(importer, activationContext);registerBootstrapBinder(contributors, activationContext, ALLOW_INACTIVE_BINDING);return contributors;
}

processInitial、processWithoutProfiles及processWithProfiles的逻辑都类似，会调用ConfigDataEnvironmentContributors#withProcessedImports方法

ConfigDataEnvironmentContributors withProcessedImports(ConfigDataImporter importer,ConfigDataActivationContext activationContext) {ImportPhase importPhase = ImportPhase.get(activationContext);this.logger.trace(LogMessage.format("Processing imports for phase %s. %s", importPhase,(activationContext != null) ? activationContext : "no activation context"));ConfigDataEnvironmentContributors result = this;int processed = 0;// 遍历所有的ConfigDataEnvironmentContributorwhile (true) {ConfigDataEnvironmentContributor contributor = getNextToProcess(result, activationContext, importPhase);if (contributor == null) {this.logger.trace(LogMessage.format("Processed imports for of %d contributors", processed));return result;}if (contributor.getKind() == Kind.UNBOUND_IMPORT) {ConfigDataEnvironmentContributor bound = contributor.withBoundProperties(result, activationContext);result = new ConfigDataEnvironmentContributors(this.logger, this.bootstrapContext,result.getRoot().withReplacement(contributor, bound));continue;}ConfigDataLocationResolverContext locationResolverContext = new ContributorConfigDataLocationResolverContext(result, contributor, activationContext);ConfigDataLoaderContext loaderContext = new ContributorDataLoaderContext(this);List<ConfigDataLocation> imports = contributor.getImports();this.logger.trace(LogMessage.format("Processing imports %s", imports));// 执行解析和加载数据Map<ConfigDataResolutionResult, ConfigData> imported = importer.resolveAndLoad(activationContext,locationResolverContext, loaderContext, imports);this.logger.trace(LogMessage.of(() -> getImportedMessage(imported.keySet())));ConfigDataEnvironmentContributor contributorAndChildren = contributor.withChildren(importPhase,asContributors(imported));result = new ConfigDataEnvironmentContributors(this.logger, this.bootstrapContext,result.getRoot().withReplacement(contributor, contributorAndChildren));processed++;}
}

调用ConfigDataImporter#resolveAndLoad

Map<ConfigDataResolutionResult, ConfigData> resolveAndLoad(ConfigDataActivationContext activationContext,ConfigDataLocationResolverContext locationResolverContext, ConfigDataLoaderContext loaderContext,List<ConfigDataLocation> locations) {try {Profiles profiles = (activationContext != null) ? activationContext.getProfiles() : null;// 解析配置文件路径List<ConfigDataResolutionResult> resolved = resolve(locationResolverContext, profiles, locations);// 加载配置文件return load(loaderContext, resolved);}catch (IOException ex) {throw new IllegalStateException("IO error on loading imports from " + locations, ex);}
}private Map<ConfigDataResolutionResult, ConfigData> load(ConfigDataLoaderContext loaderContext,List<ConfigDataResolutionResult> candidates) throws IOException {Map<ConfigDataResolutionResult, ConfigData> result = new LinkedHashMap<>();// 从后往前读取for (int i = candidates.size() - 1; i >= 0; i--) {ConfigDataResolutionResult candidate = candidates.get(i);ConfigDataLocation location = candidate.getLocation();ConfigDataResource resource = candidate.getResource();this.logger.trace(LogMessage.format("Considering resource %s from location %s", resource, location));if (resource.isOptional()) {this.optionalLocations.add(location);}if (this.loaded.contains(resource)) {this.logger.trace(LogMessage.format("Already loaded resource %s ignoring location %s", resource, location));this.loadedLocations.add(location);}else {try {// 加载配置文件ConfigData loaded = this.loaders.load(loaderContext, resource);if (loaded != null) {this.logger.trace(LogMessage.format("Loaded resource %s from location %s", resource, location));this.loaded.add(resource);this.loadedLocations.add(location);result.put(candidate, loaded);}}catch (ConfigDataNotFoundException ex) {handle(ex, location, resource);}}}return Collections.unmodifiableMap(result);
}

读取文件是从最后一个开始读取，所以配置优先级顺序从高到低为：

file:./config/*/
file:./config/
file:./
classpath:/config/
classpath:/

这里通过StandardConfigDataLoader读取配置文件，StandardConfigDataLoader#load源码如下：

public ConfigData load(ConfigDataLoaderContext context, StandardConfigDataResource resource)
throws IOException, ConfigDataNotFoundException {if (resource.isEmptyDirectory()) {return ConfigData.EMPTY;}ConfigDataResourceNotFoundException.throwIfDoesNotExist(resource, resource.getResource());StandardConfigDataReference reference = resource.getReference();Resource originTrackedResource = OriginTrackedResource.of(resource.getResource(),Origin.from(reference.getConfigDataLocation()));String name = String.format("Config resource '%s' via location '%s'", resource,reference.getConfigDataLocation());// 调用PropertySourceLoader接口加载配置文件List<PropertySource<?>> propertySources = reference.getPropertySourceLoader().load(name, originTrackedResource);PropertySourceOptions options = (resource.getProfile() != null) ? PROFILE_SPECIFIC : NON_PROFILE_SPECIFIC;return new ConfigData(propertySources, options);
}

PropertySourceLoader接口的实现类有PropertiesPropertySourceLoader和YamlPropertySourceLoader，其中PropertiesPropertySourceLoader可以加载properties和xml格式的配置文件，YamlPropertySourceLoader可以加载yml及yaml格式的配置文件