public class ConfigFileApplicationListener implements EnvironmentPostProcessor, SmartApplicationListener, Ordered {
 // Note the order is from least to most specific (last one wins)
 // 默認(rèn)檢索配置文件的路徑，優(yōu)先級越來越高，
 // 可以通過 spring.config.location重新指定，要早于當(dāng)前類執(zhí)行時配置好
 private static final String DEFAULT_SEARCH_LOCATIONS = "classpath:/,classpath:/config/,file:./,file:./config/";
 // 默認(rèn)的配置名，可以通過命令行配置--spring.config.name=xxx來重新指定
 // 不通過命令行也可以通過其他方式，環(huán)境變量這些。
 private static final String DEFAULT_NAMES = "application";
 
 private class Loader {
 // 找到配置的路徑
 private Set<String> getSearchLocations() {
  if (this.environment.containsProperty(CONFIG_LOCATION_PROPERTY)) {
  return getSearchLocations(CONFIG_LOCATION_PROPERTY);
  }
  Set<String> locations = getSearchLocations(CONFIG_ADDITIONAL_LOCATION_PROPERTY);
  locations.addAll(
  asResolvedSet(ConfigFileApplicationListener.this.searchLocations, DEFAULT_SEARCH_LOCATIONS));
  return locations;
 }
 // 解析成Set
 private Set<String> asResolvedSet(String value, String fallback) {
 List<String> list = Arrays.asList(StringUtils.trimArrayElements(StringUtils.commaDelimitedListToStringArray(
 (value != null) ? this.environment.resolvePlaceholders(value) : fallback)));
 // 這里會做一個反轉(zhuǎn)，也就是配置的路徑中，放在后面的優(yōu)先級越高
  Collections.reverse(list);
 return new LinkedHashSet<>(list);
 }
 private Set<String> getSearchNames() {
 if (this.environment.containsProperty(CONFIG_NAME_PROPERTY)) {
 String property = this.environment.getProperty(CONFIG_NAME_PROPERTY);
 return asResolvedSet(property, null);
 }
 return asResolvedSet(ConfigFileApplicationListener.this.names, DEFAULT_NAMES);
 }
 } 
}

protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
 MutablePropertySources sources = environment.getPropertySources();
 if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
 sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
 }
 // 支持從命令行添加屬性以及存在參數(shù)時
 if (this.addCommandLineProperties && args.length > 0) {
 String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
 // 這里是看下是不是存在同名的配置了
 if (sources.contains(name)) {
  PropertySource<?> source = sources.get(name);
  CompositePropertySource composite = new CompositePropertySource(name);
  composite.addPropertySource(
  new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
  composite.addPropertySource(source);
  sources.replace(name, composite);
 }
 else {
  // 直接添加，并且是添加到第一個位置，具有最高優(yōu)先級
  sources.addFirst(new SimpleCommandLinePropertySource(args));
 }
 }
}

// org.springframework.context.annotation.ConfigurationClassParser#processPropertySource
private void processPropertySource(AnnotationAttributes propertySource) throws IOException {
 String name = propertySource.getString("name");
 if (!StringUtils.hasLength(name)) {
 name = null;
 }
 String encoding = propertySource.getString("encoding");
 if (!StringUtils.hasLength(encoding)) {
 encoding = null;
 }
 // 獲取配置的文件路徑
 String[] locations = propertySource.getStringArray("value");
 Assert.isTrue(locations.length > 0, "At least one @PropertySource(value) location is required");
 boolean ignoreResourceNotFound = propertySource.getBoolean("ignoreResourceNotFound");
 // 指定的讀取配置文件的工廠
 Class<? extends PropertySourceFactory> factoryClass = propertySource.getClass("factory");
 // 沒有就用默認(rèn)的 
 PropertySourceFactory factory = (factoryClass == PropertySourceFactory.class ?
  DEFAULT_PROPERTY_SOURCE_FACTORY : BeanUtils.instantiateClass(factoryClass));
 // 循環(huán)加載
 for (String location : locations) {
 try {
  // 會解析存在占位符的情況
  String resolvedLocation = this.environment.resolveRequiredPlaceholders(location);
  // 使用DefaultResourceLoader來加載資源
  Resource resource = this.resourceLoader.getResource(resolvedLocation);
  // 創(chuàng)建PropertySource對象
  addPropertySource(factory.createPropertySource(name, new EncodedResource(resource, encoding)));
 }
 catch (IllegalArgumentException | FileNotFoundException | UnknownHostException ex) {
  // Placeholders not resolvable or resource not found when trying to open it
  if (ignoreResourceNotFound) {
  if (logger.isInfoEnabled()) {
   logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());
  }
  }
  else {
  throw ex;
  }
 }
 }
}

// @ConfigurationProperty
public class ConfigurationPropertiesBindingPostProcessor
 implements BeanPostProcessor, PriorityOrdered, ApplicationContextAware, InitializingBean {
 @Override
 public int getOrder() {
 return Ordered.HIGHEST_PRECEDENCE + 1;
 }

}
// @Value
public class AutowiredAnnotationBeanPostProcessor extends InstantiationAwareBeanPostProcessorAdapter
 implements MergedBeanDefinitionPostProcessor, PriorityOrdered, BeanFactoryAware {
 private int order = Ordered.LOWEST_PRECEDENCE - 2;
 @Override
 public int getOrder() {
 return this.order;
 }
}

@Override
public void onApplicationEvent(ApplicationEvent event) {
 if (event instanceof ApplicationEnvironmentPreparedEvent) {
 onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
 }
 if (event instanceof ApplicationPreparedEvent) {
 onApplicationPreparedEvent(event);
 }
}
private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
 List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
 postProcessors.add(this);
 AnnotationAwareOrderComparator.sort(postProcessors);
 for (EnvironmentPostProcessor postProcessor : postProcessors) {
 postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication());
 }
}

org.springframework.boot.env.EnvironmentPostProcessor=com.example.configuration.ConfigurationFileLoader

public class ConfigurationFileLoader implements EnvironmentPostProcessor {

 private static final String DEFAULT_SEARCH_LOCATIONS = "classpath:/,classpath:/config/,file:./,file:./config/";
 private static final String DEFAULT_NAMES = "download";
 private static final String DEFAULT_FILE_EXTENSION = ".yml";


 @Override
 public void postProcessEnvironment (ConfigurableEnvironment environment,
     SpringApplication application) {

 List<String> list = Arrays.asList(StringUtils.trimArrayElements(
  StringUtils.commaDelimitedListToStringArray(DEFAULT_SEARCH_LOCATIONS)));
 Collections.reverse(list);
 Set<String> reversedLocationSet = new LinkedHashSet(list);
 ResourceLoader defaultResourceLoader = new DefaultResourceLoader();
 YamlPropertiesFactoryBean yamlPropertiesFactoryBean = new YamlPropertiesFactoryBean();
 List<Properties> loadedProperties = new ArrayList<>(2);
 reversedLocationSet.forEach(location->{
  Resource resource = defaultResourceLoader.getResource(location + DEFAULT_NAMES+DEFAULT_FILE_EXTENSION);
  if (resource == null || !resource.exists()) {
  return;
  }
  yamlPropertiesFactoryBean.setResources(resource);
  Properties properties = yamlPropertiesFactoryBean.getObject();
  loadedProperties.add(properties);
 });

 Properties filteredProperties = new Properties();
 Set<Object> addedKeys = new LinkedHashSet<>();
 for (Properties propertySource : loadedProperties) {
  for (Object key : propertySource.keySet()) {
  String stringKey = (String) key;
  if (addedKeys.add(key)) {
   filteredProperties.setProperty(stringKey, propertySource.getProperty(stringKey));
  }

  }
 }
 PropertiesPropertySource propertySources = new PropertiesPropertySource(DEFAULT_NAMES, filteredProperties);
 environment.getPropertySources().addLast(propertySources);
 }
}