来源 ：宜信技术学院 作者：石建伟

一、流程分析

入口程序

在 SpringApplication#run(String... args) 方法中，外部化配置关键流程分为以下四步

public ConfigurableApplicationContext run(String... args) {    ...    SpringApplicationRunListeners listeners = getRunListeners(args); // 1    listeners.starting();    try {        ApplicationArguments applicationArguments = new DefaultApplicationArguments(            args);        ConfigurableEnvironment environment = prepareEnvironment(listeners,                                                                 applicationArguments); // 2        configureIgnoreBeanInfo(environment);        Banner printedBanner = printBanner(environment);        context = createApplicationContext();        exceptionReporters = getSpringFactoriesInstances(            SpringBootExceptionReporter.class,            new Class[] { ConfigurableApplicationContext.class }, context);        prepareContext(context, environment, listeners, applicationArguments,                       printedBanner); // 3        refreshContext(context); // 4        afterRefresh(context, applicationArguments);        stopWatch.stop();        if (this.logStartupInfo) {            new StartupInfoLogger(this.mainApplicationClass)                .logStarted(getApplicationLog(), stopWatch);        }        listeners.started(context);        callRunners(context, applicationArguments);    }    ...}

关键流程思维导图

关键流程详解

对入口程序中标记的四步，分析如下

1、SpringApplication#getRunListeners

加载 META-INF/spring.factories 获取 SpringApplicationRunListener 的实例集合，存放的对象是 EventPublishingRunListener 类型 以及自定义的 SpringApplicationRunListener 实现类型

2、SpringApplication#prepareEnvironment

prepareEnvironment 方法中，主要的三步如下

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,    ApplicationArguments applicationArguments) {    // Create and configure the environment    ConfigurableEnvironment environment = getOrCreateEnvironment(); // 2.1    configureEnvironment(environment, applicationArguments.getSourceArgs()); // 2.2    listeners.environmentPrepared(environment); // 2.3    ...    return environment;}

2.1、getOrCreateEnvironment 方法

在 WebApplicationType.SERVLET web应用类型下，会创建 StandardServletEnvironment，本文以 StandardServletEnvironment 为例，类的层次结构如下

当创建 StandardServletEnvironment ，StandardServletEnvironment 父类 AbstractEnvironment 调用 customizePropertySources 方法，会执行 StandardServletEnvironment#customizePropertySources 和 StandardEnvironment#customizePropertySources ，源码如下

AbstractEnvironment

public AbstractEnvironment() {    customizePropertySources(this.propertySources);    if (logger.isDebugEnabled()) {        logger.debug("Initialized " + getClass().getSimpleName() + " with PropertySources " + this.propertySources);    }}

StandardServletEnvironment#customizePropertySources

/** Servlet context init parameters property source name: {@value} */public static final String SERVLET_CONTEXT_PROPERTY_SOURCE_NAME = "servletContextInitParams";/** Servlet config init parameters property source name: {@value} */public static final String SERVLET_CONFIG_PROPERTY_SOURCE_NAME = "servletConfigInitParams";/** JNDI property source name: {@value} */public static final String JNDI_PROPERTY_SOURCE_NAME = "jndiProperties";@Overrideprotected void customizePropertySources(MutablePropertySources propertySources) {    propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));    propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));    if (JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {        propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));    }    super.customizePropertySources(propertySources);}

StandardEnvironment#customizePropertySources

/** System environment property source name: {@value} */public static final String SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME = "systemEnvironment";/** JVM system properties property source name: {@value} */public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";@Overrideprotected void customizePropertySources(MutablePropertySources propertySources) {    propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));    propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,getSystemEnvironment());}

PropertySources 顺序：

1. servletConfigInitParams
2. servletContextInitParams
3. jndiProperties
4. systemProperties
5. systemEnvironment

PropertySources 与

PropertySource 关系为 1 对 N

2.2、configureEnvironment 方法

调用 configurePropertySources(environment, args)， 在方法里面设置 Environment 的 PropertySources ， 包含 defaultProperties 和 SimpleCommandLinePropertySource （commandLineArgs），PropertySources 添加 defaultProperties 到最后，添加 SimpleCommandLinePropertySource （commandLineArgs）到最前面

PropertySources 顺序：

1. commandLineArgs
2. servletConfigInitParams
3. servletContextInitParams
4. jndiProperties
5. systemProperties
6. systemEnvironment
7. defaultProperties

2.3、listeners.environmentPrepared 方法

会按优先级顺序遍历执行 SpringApplicationRunListener#environmentPrepared，比如 EventPublishingRunListener 和 自定义的 SpringApplicationRunListener

• EventPublishingRunListener 发布 ApplicationEnvironmentPreparedEvent 事件

  • ConfigFileApplicationListener 监听 ApplicationEvent 事件 、处理 ApplicationEnvironmentPreparedEvent 事件，加载所有 EnvironmentPostProcessor 包括自己，然后按照顺序进行方法回调

    • ConfigFileApplicationListener#postProcessEnvironment 方法回调 ，然后addPropertySources 方法调用 RandomValuePropertySource#addToEnvironment，在 systemEnvironment 后面添加 random，然后添加配置文件的属性源（详见源码 ConfigFileApplicationListener.Loader#load()

• 扩展点

  • 自定义 SpringApplicationRunListener ，重写 environmentPrepared 方法
  • 自定义 EnvironmentPostProcessor
  • 自定义 ApplicationListener 监听 ApplicationEnvironmentPreparedEvent 事件

ConfigFileApplicationListener，即是 EnvironmentPostProcessor ，又是 ApplicationListener ，类的层次结构如下

@Overridepublic void onApplicationEvent(ApplicationEvent event) {    // 处理 ApplicationEnvironmentPreparedEvent 事件    if (event instanceof ApplicationEnvironmentPreparedEvent) {        onApplicationEnvironmentPreparedEvent(            (ApplicationEnvironmentPreparedEvent) event);    }    // 处理 ApplicationPreparedEvent 事件    if (event instanceof ApplicationPreparedEvent) {        onApplicationPreparedEvent(event);    }}private void onApplicationEnvironmentPreparedEvent(    ApplicationEnvironmentPreparedEvent event) {    // 加载 META-INF/spring.factories 中配置的 EnvironmentPostProcessor    List
    
      postProcessors = loadPostProcessors();    // 加载自己 ConfigFileApplicationListener    postProcessors.add(this);    // 按照 Ordered 进行优先级排序    AnnotationAwareOrderComparator.sort(postProcessors);    // 回调 EnvironmentPostProcessor    for (EnvironmentPostProcessor postProcessor : postProcessors) {        postProcessor.postProcessEnvironment(event.getEnvironment(),                                             event.getSpringApplication());    }}List
     
       loadPostProcessors() {    return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class,                                               getClass().getClassLoader());}@Overridepublic void postProcessEnvironment(ConfigurableEnvironment environment,                                   SpringApplication application) {    addPropertySources(environment, application.getResourceLoader());}/**  * Add config file property sources to the specified environment.  * @param environment the environment to add source to  * @param resourceLoader the resource loader  * @see #addPostProcessors(ConfigurableApplicationContext)  */protected void addPropertySources(ConfigurableEnvironment environment,                                  ResourceLoader resourceLoader) {    RandomValuePropertySource.addToEnvironment(environment);    // 添加配置文件的属性源    new Loader(environment, resourceLoader).load();}
     
    

RandomValuePropertySource

public static void addToEnvironment(ConfigurableEnvironment environment) {    // 在 systemEnvironment 后面添加 random    environment.getPropertySources().addAfter(        StandardEnvironment.SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME,        new RandomValuePropertySource(RANDOM_PROPERTY_SOURCE_NAME));    logger.trace("RandomValuePropertySource add to Environment");}

添加配置文件的属性源：

执行 new Loader(environment, resourceLoader).load(); ， 调用 load(Profile, DocumentFilterFactory, DocumentConsumer) （getSearchLocations() 获取配置文件位置，可以指定通过 spring.config.additional-location 、spring.config.location 、spring.config.name 参数或者使用默认值 ）， 然后调用 addLoadedPropertySources -> addLoadedPropertySource （加载 查找出来的 PropertySource 到 PropertySources，并确保放置到 defaultProperties 的前面 ）

默认的查找位置，配置为 "classpath:/,classpath:/config/,file:./,file:./config/" ，查找顺序从后向前

PropertySources 顺序：

1. commandLineArgs
2. servletConfigInitParams
3. servletContextInitParams
4. jndiProperties
5. systemProperties
6. systemEnvironment
7. random
8. application.properties ...
9. defaultProperties

3、SpringApplication#prepareContext

prepareContext 方法中，主要的三步如下

private void prepareContext(ConfigurableApplicationContext context,                            ConfigurableEnvironment environment,                             SpringApplicationRunListeners listeners,                            ApplicationArguments applicationArguments,                             Banner printedBanner) {    ...    applyInitializers(context); // 3.1    listeners.contextPrepared(context); //3.2    ...    listeners.contextLoaded(context); // 3.3}

3.1、applyInitializers 方法

会遍历执行所有的 ApplicationContextInitializer#initialize

• 扩展点

  • 自定义 ApplicationContextInitializer

3.2、listeners.contextPrepared 方法

会按优先级顺序遍历执行 SpringApplicationRunListener#contextPrepared，比如 EventPublishingRunListener 和 自定义的 SpringApplicationRunListener

• 扩展点

  • 自定义 SpringApplicationRunListener ，重写 contextPrepared 方法

3.3、listeners.contextLoaded 方法

会按优先级顺序遍历执行 SpringApplicationRunListener#contextLoaded ，比如 EventPublishingRunListener 和 自定义的 SpringApplicationRunListener

• EventPublishingRunListener 发布 ApplicationPreparedEvent 事件

  • ConfigFileApplicationListener 监听 ApplicationEvent 事件 处理 ApplicationPreparedEvent 事件

• 扩展点

  • 自定义 SpringApplicationRunListener ，重写 contextLoaded 方法
  • 自定义 ApplicationListener ，监听 ApplicationPreparedEvent 事件

ConfigFileApplicationListener

@Overridepublic void onApplicationEvent(ApplicationEvent event) {    // 处理 ApplicationEnvironmentPreparedEvent 事件    if (event instanceof ApplicationEnvironmentPreparedEvent) {        onApplicationEnvironmentPreparedEvent(            (ApplicationEnvironmentPreparedEvent) event);    }    // 处理 ApplicationPreparedEvent 事件    if (event instanceof ApplicationPreparedEvent) {        onApplicationPreparedEvent(event);    }}private void onApplicationPreparedEvent(ApplicationEvent event) {    this.logger.replayTo(ConfigFileApplicationListener.class);    addPostProcessors(((ApplicationPreparedEvent) event).getApplicationContext());}// 添加 PropertySourceOrderingPostProcessor 处理器，配置 PropertySourcesprotected void addPostProcessors(ConfigurableApplicationContext context) {    context.addBeanFactoryPostProcessor(        new PropertySourceOrderingPostProcessor(context));}

PropertySourceOrderingPostProcessor

// 回调处理（在配置类属性源解析）@Overridepublic void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)    throws BeansException {    reorderSources(this.context.getEnvironment());}// 调整 PropertySources 顺序，先删除 defaultProperties， 再把 defaultProperties 添加到最后private void reorderSources(ConfigurableEnvironment environment) {    PropertySource
     defaultProperties = environment.getPropertySources()        .remove(DEFAULT_PROPERTIES);    if (defaultProperties != null) {        environment.getPropertySources().addLast(defaultProperties);    }}

PropertySourceOrderingPostProcessor 是

BeanFactoryPostProcessor

4、SpringApplication#refreshContext

会进行 @Configuration 配置类属性源解析，处理 @PropertySource annotations on your @Configuration classes，但顺序是在 defaultProperties 之后，下面会把 defaultProperties 调整到最后

AbstractApplicationContext#refresh 调用 invokeBeanFactoryPostProcessors (PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors)， 然后进行 BeanFactoryPostProcessor 的回调处理 ，比如 PropertySourceOrderingPostProcessor 的回调（源码见上文）

PropertySources 顺序：

1. commandLineArgs
2. servletConfigInitParams
3. servletContextInitParams
4. jndiProperties
5. systemProperties
6. systemEnvironment
7. random
8. application.properties ...
9. @PropertySource annotations on your @Configuration classes
10. defaultProperties

不推荐使用这种方式，推荐使用在 refreshContext 之前准备好，

@PropertySource 加载太晚，不会对自动配置产生任何影响

二、扩展外部化配置属性源

1、基于 EnvironmentPostProcessor 扩展

public class CustomEnvironmentPostProcessor implements EnvironmentPostProcessor

2、基于 ApplicationEnvironmentPreparedEvent 扩展

public class ApplicationEnvironmentPreparedEventListener implements ApplicationListener
    

3、基于 SpringApplicationRunListener 扩展

public class CustomSpringApplicationRunListener implements SpringApplicationRunListener, Ordered

可以重写方法 environmentPrepared、contextPrepared、contextLoaded 进行扩展

4、基于 ApplicationContextInitializer 扩展

public class CustomApplicationContextInitializer implements ApplicationContextInitializer

关于与 Spring Cloud Config Client 整合，对外部化配置加载的扩展（绑定到Config Server，使用远端的property sources 初始化

Environment），参考源码

PropertySourceBootstrapConfiguration（是对

ApplicationContextInitializer 的扩展）、

ConfigServicePropertySourceLocator#locate

获取远端的property sources是 RestTemplate 通过向 http://{spring.cloud.config.uri}/{spring.application.name}/{spring.cloud.config.profile}/{spring.cloud.config.label} 发送 GET 请求方式获取的

5、基于 ApplicationPreparedEvent 扩展

public class ApplicationPreparedEventListener implements ApplicationListener
    

6、扩展实战

6.1、扩展配置

在 classpath 下添加配置文件 META-INF/spring.factories， 内容如下

# Spring Application Run Listenersorg.springframework.boot.SpringApplicationRunListener=\springboot.propertysource.extend.listener.CustomSpringApplicationRunListener# Application Context Initializersorg.springframework.context.ApplicationContextInitializer=\springboot.propertysource.extend.initializer.CustomApplicationContextInitializer# Application Listenersorg.springframework.context.ApplicationListener=\springboot.propertysource.extend.event.listener.ApplicationEnvironmentPreparedEventListener,\springboot.propertysource.extend.event.listener.ApplicationPreparedEventListener# Environment Post Processorsorg.springframework.boot.env.EnvironmentPostProcessor=\springboot.propertysource.extend.processor.CustomEnvironmentPostProcessor

以上的扩展可以选取其中一种进行扩展，只是属性源的加载时机不太一样

6.2、扩展实例代码

PropertySources 顺序：

propertySourceName: [ApplicationPreparedEventListener], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [CustomSpringApplicationRunListener-contextLoaded], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [CustomSpringApplicationRunListener-contextPrepared], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [CustomApplicationContextInitializer], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [bootstrapProperties], propertySourceClassName: [CompositePropertySource]propertySourceName: [configurationProperties], propertySourceClassName: [ConfigurationPropertySourcesPropertySource]propertySourceName: [CustomSpringApplicationRunListener-environmentPrepared], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [CustomEnvironmentPostProcessor-dev-application], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [ApplicationEnvironmentPreparedEventListener], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [commandLineArgs], propertySourceClassName: [SimpleCommandLinePropertySource]propertySourceName: [servletConfigInitParams], propertySourceClassName: [StubPropertySource]propertySourceName: [servletContextInitParams], propertySourceClassName: [ServletContextPropertySource]propertySourceName: [systemProperties], propertySourceClassName: [MapPropertySource]propertySourceName: [systemEnvironment], propertySourceClassName: [OriginAwareSystemEnvironmentPropertySource]propertySourceName: [random], propertySourceClassName: [RandomValuePropertySource]propertySourceName: [applicationConfig: [classpath:/extend/config/springApplicationRunListener.properties]], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [applicationConfig: [classpath:/extend/config/applicationListener.properties]], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [applicationConfig: [classpath:/extend/config/applicationContextInitializer.properties]], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [applicationConfig: [classpath:/extend/config/environmentPostProcessor.properties]], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [applicationConfig: [classpath:/extend/config/application.properties]], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [applicationConfig: [classpath:/extend/config/config.properties]], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [applicationConfig: [classpath:/application.properties]], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [springCloudClientHostInfo], propertySourceClassName: [MapPropertySource]propertySourceName: [applicationConfig: [classpath:/bootstrap.properties]], propertySourceClassName: [OriginTrackedMapPropertySource]propertySourceName: [propertySourceConfig], propertySourceClassName: [ResourcePropertySource]propertySourceName: [defaultProperties], propertySourceClassName: [MapPropertySource]

bootstrapProperties 是 获取远端（config-server）的 property sources

加载顺序也可参考 http://{host}:{port}/actuator/env

PropertySources 单元测试顺序：

@TestPropertySource#properties@SpringBootTest#properties@TestPropertySource#locations

三、参考资料