public abstract class PropertySource<T> {

 protected final Log logger = LogFactory.getLog(getClass());

 protected final String name;

 protected final T source;

 public PropertySource(String name, T source) {
 Assert.hasText(name, "Property source name must contain at least one character");
 Assert.notNull(source, "Property source must not be null");
 this.name = name;
 this.source = source;
 }

 @SuppressWarnings("unchecked")
 public PropertySource(String name) {
 this(name, (T) new Object());
 }

 public String getName() {
 return this.name;
 }

 public T getSource() {
 return this.source;
 } 

 public boolean containsProperty(String name) {
 return (getProperty(name) != null);
 } 

 @Nullable
 public abstract Object getProperty(String name); 

 @Override
 public boolean equals(Object obj) {
 return (this == obj || (obj instanceof PropertySource &&
 ObjectUtils.nullSafeEquals(this.name, ((PropertySource<?>) obj).name)));
 } 

 @Override
 public int hashCode() {
 return ObjectUtils.nullSafeHashCode(this.name);
 } 
//省略其他方法和內部類的源碼 
}

public static final String IGNORE_GETENV_PROPERTY_NAME = "spring.getenv.ignore";
public static final String ACTIVE_PROFILES_PROPERTY_NAME = "spring.profiles.active";
public static final String DEFAULT_PROFILES_PROPERTY_NAME = "spring.profiles.default";
protected static final String RESERVED_DEFAULT_PROFILE_NAME = "default";

private final Set<String> activeProfiles = new LinkedHashSet<>();

private final Set<String> defaultProfiles = new LinkedHashSet<>(getReservedDefaultProfiles());

private final MutablePropertySources propertySources = new MutablePropertySources(this.logger);

private final ConfigurablePropertyResolver propertyResolver = new PropertySourcesPropertyResolver(this.propertySources);

private final List<PropertySource<?>> propertySourceList = new CopyOnWriteArrayList<>();

public void addBefore(String relativePropertySourceName, PropertySource<?> propertySource) {
 if (logger.isDebugEnabled()) {
 logger.debug("Adding PropertySource '" + propertySource.getName() +
  "' with search precedence immediately higher than '" + relativePropertySourceName + "'");
 }
 //前一個PropertySource的name指定為relativePropertySourceName時候必須和添加的PropertySource的name屬性不相同
 assertLegalRelativeAddition(relativePropertySourceName, propertySource);
 //嘗試移除同名的PropertySource
 removeIfPresent(propertySource);
 //獲取前一個PropertySource在CopyOnWriteArrayList中的索引
 int index = assertPresentAndGetIndex(relativePropertySourceName);
 //添加當前傳入的PropertySource到指定前一個PropertySource的索引，相當于relativePropertySourceName對應的PropertySource后移到原來索引值+1的位置
 addAtIndex(index, propertySource);
}

protected void assertLegalRelativeAddition(String relativePropertySourceName, PropertySource<?> propertySource) {
 String newPropertySourceName = propertySource.getName();
 if (relativePropertySourceName.equals(newPropertySourceName)) {
 throw new IllegalArgumentException(
  "PropertySource named '" + newPropertySourceName + "' cannot be added relative to itself");
 }
}

protected void removeIfPresent(PropertySource<?> propertySource) {
 this.propertySourceList.remove(propertySource);
}

private int assertPresentAndGetIndex(String name) {
 int index = this.propertySourceList.indexOf(PropertySource.named(name));
 if (index == -1) {
 throw new IllegalArgumentException("PropertySource named '" + name + "' does not exist");
 }
 return index;
}

private void addAtIndex(int index, PropertySource<?> propertySource) {
 //注意，這里會再次嘗試移除同名的PropertySource
 removeIfPresent(propertySource);
 this.propertySourceList.add(index, propertySource);
}

MutablePropertySources mutablePropertySources = new MutablePropertySources();
Map<String, Object> map = new HashMap<>(8);
map.put("name", "throwable");
map.put("age", 25);
MapPropertySource mapPropertySource = new MapPropertySource("map", map);
mutablePropertySources.addLast(mapPropertySource);
Properties properties = new Properties();
PropertiesPropertySource propertiesPropertySource = new PropertiesPropertySource("prop", properties);
properties.put("name", "doge");
properties.put("gourp", "group-a");
mutablePropertySources.addBefore("map", propertiesPropertySource);
System.out.println(mutablePropertySources);

 private ConfigurableEnvironment prepareEnvironment(
 SpringApplicationRunListeners listeners,
 ApplicationArguments applicationArguments) {
 // Create and configure the environment
 //創(chuàng)建ConfigurableEnvironment實例
 ConfigurableEnvironment environment = getOrCreateEnvironment();
 //啟動參數(shù)綁定到ConfigurableEnvironment中
 configureEnvironment(environment, applicationArguments.getSourceArgs());
 //發(fā)布ConfigurableEnvironment準備完畢事件
 listeners.environmentPrepared(environment);
 //綁定ConfigurableEnvironment到當前的SpringApplication實例中
 bindToSpringApplication(environment);
 //這一步是非SpringMVC項目的處理，暫時忽略
 if (this.webApplicationType == WebApplicationType.NONE) {
 environment = new EnvironmentConverter(getClassLoader())
  .convertToStandardEnvironmentIfNecessary(environment);
 }
 //綁定ConfigurationPropertySourcesPropertySource到ConfigurableEnvironment中，name為configurationProperties，實例是SpringConfigurationPropertySources，屬性實際是ConfigurableEnvironment中的MutablePropertySources
 ConfigurationPropertySources.attach(environment);
 return environment;
 }

private ConfigurableEnvironment getOrCreateEnvironment() {
 if (this.environment != null) {
 return this.environment;
 }
 //在SpringMVC項目，ConfigurableEnvironment接口的實例就是新建的StandardServletEnvironment實例
 if (this.webApplicationType == WebApplicationType.SERVLET) {
 return new StandardServletEnvironment();
 }
 return new StandardEnvironment();
}
//REACTIVE_WEB_ENVIRONMENT_CLASS=org.springframework.web.reactive.DispatcherHandler
//MVC_WEB_ENVIRONMENT_CLASS=org.springframework.web.servlet.DispatcherServlet
//MVC_WEB_ENVIRONMENT_CLASS={"javax.servlet.Servlet","org.springframework.web.context.ConfigurableWebApplicationContext"}
//這里，默認就是WebApplicationType.SERVLET
private WebApplicationType deduceWebApplicationType() {
 if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
 && !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
 return WebApplicationType.REACTIVE;
 }
 for (String className : WEB_ENVIRONMENT_CLASSES) {
 if (!ClassUtils.isPresent(className, null)) {
 return WebApplicationType.NONE;
 }
 }
 return WebApplicationType.SERVLET;
}

private void onApplicationEnvironmentPreparedEvent(
 ApplicationEnvironmentPreparedEvent event) {
 List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
 postProcessors.add(this);
 AnnotationAwareOrderComparator.sort(postProcessors);
 //遍歷所有的EnvironmentPostProcessor對Environment實例進行處理
 for (EnvironmentPostProcessor postProcessor : postProcessors) {
 postProcessor.postProcessEnvironment(event.getEnvironment(),
  event.getSpringApplication());
 }
}

//從spring.factories文件中加載，一共有四個實例
//ConfigFileApplicationListener
//CloudFoundryVcapEnvironmentPostProcessor
//SpringApplicationJsonEnvironmentPostProcessor
//SystemEnvironmentPropertySourceEnvironmentPostProcessor
List<EnvironmentPostProcessor> loadPostProcessors() {
 return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class,
 getClass().getClassLoader());
}

public void postProcessEnvironment(ConfigurableEnvironment environment,
 SpringApplication application) {
 addPropertySources(environment, application.getResourceLoader());
}

protected void addPropertySources(ConfigurableEnvironment environment,
 ResourceLoader resourceLoader) {
 RandomValuePropertySource.addToEnvironment(environment);
 new Loader(environment, resourceLoader).load();
}

@Nullable
private final PropertySources propertySources;

public PropertySourcesPropertyResolver(@Nullable PropertySources propertySources) {
 this.propertySources = propertySources;
 }

protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) {
 if (this.propertySources != null) {
 //遍歷所有的PropertySource
 for (PropertySource<?> propertySource : this.propertySources) {
 if (logger.isTraceEnabled()) {
 logger.trace("Searching for key '" + key + "' in PropertySource '" +
  propertySource.getName() + "'");
 }
 Object value = propertySource.getProperty(key);
 //選用第一個不為null的匹配key的屬性值
 if (value != null) {
 if (resolveNestedPlaceholders && value instanceof String) {
  //處理屬性占位符，如${server.port}，底層委托到PropertyPlaceholderHelper完成
  value = resolveNestedPlaceholders((String) value);
 }
 logKeyFound(key, propertySource, value);
 //如果需要的話，進行一次類型轉換，底層委托到DefaultConversionService完成
 return convertValueIfNecessary(value, targetValueType);
 }
 }
 }
 if (logger.isDebugEnabled()) {
 logger.debug("Could not find key '" + key + "' in any property source");
 }
 return null;
}