Spring Boot 外部化配置实战解析

来源：[宜信技术学院 ]

做者：石建伟

1、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如下四步

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);
    }
    ...
}

关键流程思惟导图

关键流程详解

对入口程序中标记的四步，分析以下

一、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

二、SpringApplication#prepareEnvironment

prepareEnvironment 方法中，主要的三步以下

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;
}

2.一、getOrCreateEnvironment 方法

在 WebApplicationType.SERVLET web应用类型下，会建立 StandardServletEnvironment，本文以 StandardServletEnvironment 为例，类的层次结构以下

当建立 StandardServletEnvironment ，StandardServletEnvironment 父类 AbstractEnvironment 调用 customizePropertySources 方法，会执行 StandardServletEnvironment#customizePropertySources 和 StandardEnvironment#customizePropertySources ，源码以下

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";

@Override
protected 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";

@Override
protected 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

2.二、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

2.三、listeners.environmentPrepared 方法

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

• EventPublishingRunListener 发布 ApplicationEnvironmentPreparedEvent 事件

• ConfigFileApplicationListener 监听 ApplicationEvent 事件 、处理 ApplicationEnvironmentPreparedEvent 事件，加载全部 EnvironmentPostProcessor 包括本身，而后按照顺序进行方法回调

  • ConfigFileApplicationListener#postProcessEnvironment 方法回调 ，而后addPropertySources 方法调用 RandomValuePropertySource#addToEnvironment，在 systemEnvironment 后面添加 random，而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，便是 EnvironmentPostProcessor ，又是 ApplicationListener ，类的层次结构以下

@Override
public 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<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
    // 加载本身 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<EnvironmentPostProcessor> loadPostProcessors() {
    return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class,
                                               getClass().getClassLoader());
}

@Override
public 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，能够指定经过 spring.config.additional-location 、spring.config.location 、spring.config.name 参数或者使用默认值 ）， 而后调用 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

三、SpringApplication#prepareContext

prepareContext 方法中，主要的三步以下

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
}

3.一、applyInitializers 方法

会遍历执行全部的 ApplicationContextInitializer#initialize

• 扩展点
• 自定义 ApplicationContextInitializer

3.二、listeners.contextPrepared 方法

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

• 扩展点
• 自定义 SpringApplicationRunListener ，重写 contextPrepared 方法

3.三、listeners.contextLoaded 方法

会按优先级顺序遍历执行 SpringApplicationRunListener#contextLoaded，好比 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

@Override
public 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 PropertySources
protected void addPostProcessors(ConfigurableApplicationContext context) {
    context.addBeanFactoryPostProcessor(
        new PropertySourceOrderingPostProcessor(context));
}

PropertySourceOrderingPostProcessor

// 回调处理（在配置类属性源解析）
@Override
public 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

四、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 以后，下面会把 defaultProperties 调整到最后

AbstractApplicationContext#refresh 调用 invokeBeanFactoryPostProcessors (PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors)， 而后进行 BeanFactoryPostProcessor 的回调处理 ，好比 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 以前准备好，@PropertySource 加载太晚，不会对自动配置产生任何影响

2、扩展外部化配置属性源

一、基于 EnvironmentPostProcessor 扩展

public class CustomEnvironmentPostProcessor implements EnvironmentPostProcessor

二、基于 ApplicationEnvironmentPreparedEvent 扩展

public class ApplicationEnvironmentPreparedEventListener implements ApplicationListener<ApplicationEnvironmentPreparedEvent>

三、基于 SpringApplicationRunListener 扩展

public class CustomSpringApplicationRunListener implements SpringApplicationRunListener, Ordered

能够重写方法 environmentPrepared、contextPrepared、contextLoaded 进行扩展

四、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 经过向 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

五、基于 ApplicationPreparedEvent 扩展

public class ApplicationPreparedEventListener implements ApplicationListener<ApplicationPreparedEvent>

六、扩展实战

6.一、扩展配置

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

# Spring Application Run Listeners
org.springframework.boot.SpringApplicationRunListener=\
springboot.propertysource.extend.listener.CustomSpringApplicationRunListener

# Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
springboot.propertysource.extend.initializer.CustomApplicationContextInitializer

# Application Listeners
org.springframework.context.ApplicationListener=\
springboot.propertysource.extend.event.listener.ApplicationEnvironmentPreparedEventListener,\
springboot.propertysource.extend.event.listener.ApplicationPreparedEventListener

# Environment Post Processors
org.springframework.boot.env.EnvironmentPostProcessor=\
springboot.propertysource.extend.processor.CustomEnvironmentPostProcessor

以上的扩展能够选取其中一种进行扩展，只是属性源的加载时机不太同样

6.二、扩展实例代码

https://github.com/shijw823/springboot-externalized-configuration-extend.git

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

3、参考资料

https://docs.spring.io/spring-boot/docs/2.0.5.RELEASE/reference/htmlsingle/#boot-features-external-config