SpringBoot配置文件的加载原理和优先级

我们都知道:

• SpringBoot 既可以加载指定目录下的配置文件获取配置项;
• 也可以通过启动参数（VM Options）传入配置项;

在跟踪源代码之前，先提一个问题：
当我们在通过启动参数传入的配置项时候优先使用呢,即会“顶掉”配置文件中的配置？

1.通过启动参数传入配置项

示例:

1.1 application.yml

server.port: 8888
spring.profiles.active: dev

1.2 application-dev.yml

spring.think: hello

1.3 在IDEA中使用命令行配置项

VM Options :

-Dserver.port=5555

如下图：

1.4 启动结果

Tomcat started on port(s): 5555 (http) with context path ‘’

结果:同时在application.yml 和 启动参数（VM options）中设置 server.port， 最终采用了 启动参数 中的值。

接下来开始从main函数启动处，跟入SpringBoot源码，看看SpringBoot是如何处理的。

2.系统说明

JDK：1.8
SpringBoot 版本： 2.1.7.RELEASE
IDE： IntelliJ IDEA 2018.1

3.启动参数传入配置项

跟踪源码：

可查看如下Spring Boot 2.1.7版本的执行流程。
SpringBoot2原理—SpringApplication的执行流程

当看到3.6 创建 Environment 节如下代码时候：

ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);configureIgnoreBeanInfo(environment);

有截图

通过IDEA 一行行debug可以看到是在 prepareEnvironment方法执行后，server.port 配置项才被加载入 environment 环境配置中。说明prepareEnvironment方法做的事情就是将server.port 配置项才加载到 environment 环境配置中。因此，我们重新打断点跟入prepareEnvironment方法。

#SpringApplication.javaprivate ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments) {// Create and configure the environment//跟入getOrCreateEnvironment()ConfigurableEnvironment environment = getOrCreateEnvironment();configureEnvironment(environment, applicationArguments.getSourceArgs());listeners.environmentPrepared(environment);bindToSpringApplication(environment);if (!this.isCustomEnvironment) {environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());}ConfigurationPropertySources.attach(environment);return environment;}

同样的套路，通过debug发现实在getOrCreateEnvironment方法执行后得到server.port的值 。

#SpringApplication.javaprivate ConfigurableEnvironment getOrCreateEnvironment() {if (this.environment != null) {return this.environment;}switch (this.webApplicationType) {case SERVLET:return new StandardServletEnvironment();case REACTIVE:return new StandardReactiveWebEnvironment();default://跟入StandardEnvironmentreturn new StandardEnvironment();}}

虚拟机启动参数的加载 是在StandardServletEnvironment 的实例化过程中完成的。
跟入StandardServletEnvironment的实例化过程之前，大家需要先了解 Java模板模式 。
看一下StandardServletEnvironment的类继承关系图（通过IDEA 右键 类名 --> Diagrams --> Show Diagrams Popup 即可显示下图）

抽象父类AbstractEnvironment的实例化方法中，调用了可由子类继承的customizePropertySources方法。

#AbstractEnvironment.java//跟入AbstractEnvironment构造方法
public AbstractEnvironment() {customizePropertySources(this.propertySources);}

实体化的过程中回过头来调用了子类StandardServletEnvironment的customizePropertySources方法.

#StandardServletEnvironment.java
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));}//跟入super.customizePropertySources(propertySources);}

又调用了父类StandardEnvironment的customizePropertySources方法.

#StandardEnvironment.java
protected void customizePropertySources(MutablePropertySources propertySources) {//跟入getSystemProperties()方法propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));}

有截图

通过IDEA 的变量监听功能，可以看到正是StandardEnvironment类的getSystemProperties()方法获取到了之前设置的虚拟机启动参数server.port的值。

继续跟进去。

#AbstractEnvironment.java
public Map<String, Object> getSystemProperties() {try {//跟入return (Map) System.getProperties();}

#System.javapublic static Properties getProperties() {SecurityManager sm = getSecurityManager();if (sm != null) {sm.checkPropertiesAccess();}return props;}

我们搜索一下有没有什么地方初始化 props。

#System.javaprivate static Properties props;private static native Properties initProperties(Properties props);

发现了静态方法 initProperties，从方法名上即可知道在类被加载的时候 就初始化了 props， 这是个本地方法，继续跟的话需要看对应的C++代码。

回到StandardEnvironment类的customizePropertySources方法。

protected void customizePropertySources(MutablePropertySources propertySources) {//public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";//跟入MapPropertySourcepropertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));}

MutablePropertySources是PropertySources的实现类。

#MutablePropertySources.java/*** Add the given property source object with lowest precedence.* 添加属性源，并使其优先级最低*/public void addLast(PropertySource<?> propertySource) {

再看一下MutablePropertySources的类注释。

/*** <p>Where <em>precedence</em> is mentioned in methods such as {@link #addFirst}* and {@link #addLast}, this is with regard to the order in which property sources* will be searched when resolving a given property with a {@link PropertyResolver}.** addFist 和 add Last 会设置属性源的优先级，* PropertyResolver解析配置时会根据优先级使用配置源* * @author Chris Beams* @author Juergen Hoeller* @since 3.1* @see PropertySourcesPropertyResolver*/

4.加载指定目录下的配置文件

此时我们已经看到虚拟机的启动参数先添加到系统当中，那么后面添加进来的Property Source属性源的优先级是否比 SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME(systemProperties) 属性源的优先级高呢？

回到SpringApplication的prepareEnvironment方法。

##SpringApplication.javaprivate ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments) {// Create and configure the environmentConfigurableEnvironment environment = getOrCreateEnvironment();configureEnvironment(environment, applicationArguments.getSourceArgs());listeners.environmentPrepared(environment);bindToSpringApplication(environment);if (!this.isCustomEnvironment) {environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());}ConfigurationPropertySources.attach(environment);return environment;}

同样的debug套路发现listeners.environmentPrepared执行后，application.yml 和 application-dev.yml 两个配置文件的配置项都被加载完成，所以我们继续跟入environmentPrepared方法。
在跟入environmentPrepared方法之前，需要了解 Java事件监听机制

跟入environmentPrepared中的源码。

#SpringApplicationRunListeners.javapublic void environmentPrepared(ConfigurableEnvironment environment) {for (SpringApplicationRunListener listener : this.listeners) {//跟入listener.environmentPrepared(environment);}}

#EventPublishingRunListener.javapublic void environmentPrepared(ConfigurableEnvironment environment) {//广播ApplicationEnvrionmentPreparedEvnet事件//跟入this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent(this.application, this.args, environment));}

#SimpleApplicationEventMulticaster.javapublic void multicastEvent(ApplicationEvent event) {//跟入multicastEvent(event, resolveDefaultEventType(event));}@Overridepublic void multicastEvent(final ApplicationEvent event, @Nullable ResolvableType eventType) {ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event));//注意此时 getApplicationListeners(event, type) 返回结果//包含 监听器 *ConfigFileApplicationListener*for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) {Executor executor = getTaskExecutor();if (executor != null) {executor.execute(() -> invokeListener(listener, event));}else {//跟入invokeListener(listener, event);}}}

#SimpleApplicationEventMulticaster.java/*** Invoke the given listener with the given event.* 调用对应事件的监听者* @param listener the ApplicationListener to invoke* @param event the current event to propagate* @since 4.1*/protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) {ErrorHandler errorHandler = getErrorHandler();if (errorHandler != null) {try {doInvokeListener(listener, event);}catch (Throwable err) {errorHandler.handleError(err);}}else {//跟入doInvokeListener(listener, event);}}private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) {try {//跟入listener.onApplicationEvent(event);}

#ApplicationListener.java//实现接口的监听器当中，有并跟入ConfigFileApplicationListener的实现void onApplicationEvent(E event);

public void onApplicationEvent(ApplicationEvent event) {if (event instanceof ApplicationEnvironmentPreparedEvent) {//跟入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) {//跟入：当postProcessor 为 ConfigFileApplicationListenerpostProcessor.postProcessEnvironment(event.getEnvironment(),event.getSpringApplication());}}

#ConfigFileApplicationListener.javapublic void postProcessEnvironment(ConfigurableEnvironment environment,SpringApplication application) {//跟入addPropertySources(environment, application.getResourceLoader());}protected void addPropertySources(ConfigurableEnvironment environment,ResourceLoader resourceLoader) {//environment的属性源中包含 systemProperties 属性源 即包含 server.port启动参数RandomValuePropertySource.addToEnvironment(environment);//跟入 load()方法new Loader(environment, resourceLoader).load();}

跟入load之前，需要了解 java lambda表达式。

#ConfigFileApplicationListener.java
public void load() {this.profiles = new LinkedList<>();this.processedProfiles = new LinkedList<>();this.activatedProfiles = false;this.loaded = new LinkedHashMap<>();initializeProfiles();while (!this.profiles.isEmpty()) {Profile profile = this.profiles.poll();if (profile != null && !profile.isDefaultProfile()) {addProfileToEnvironment(profile.getName());}load(profile, this::getPositiveProfileFilter,addToLoaded(MutablePropertySources::addLast, false));this.processedProfiles.add(profile);}resetEnvironmentProfiles(this.processedProfiles);//跟入load(null, this::getNegativeProfileFilter,addToLoaded(MutablePropertySources::addFirst, true));addLoadedPropertySources();}

#ConfigFileApplicationListener.javaprivate void load(Profile profile, DocumentFilterFactory filterFactory,DocumentConsumer consumer) {//getSearchLocations()默认返回：//[./config/, file:./, classpath:/config/, classpath:/]//即搜索这些路径下的文件getSearchLocations().forEach((location) -> {boolean isFolder = location.endsWith("/");//getSearchNames()返回：applicationSet<String> names = isFolder ? getSearchNames() : NO_SEARCH_NAMES;//跟入load(.....)names.forEach((name) -> load(location, name, profile, filterFactory, consumer));});}

#ConfigFileApplicationListener.java
private void load(String location, String name, Profile profile,DocumentFilterFactory filterFactory, DocumentConsumer consumer) {//name默认为：application，所以这个if分支略过if (!StringUtils.hasText(name)) {for (PropertySourceLoader loader : this.propertySourceLoaders) {if (canLoadFileExtension(loader, location)) {load(loader, location, profile,filterFactory.getDocumentFilter(profile), consumer);return;}}}Set<String> processed = new HashSet<>();//this.propertySourceLoaders: PropertiesPropertySourceLoader,YamlPropertySourceLoaderfor (PropertySourceLoader loader : this.propertySourceLoaders) {//PropertiesPropertySourceLoader.getFileExtensions(): properties, xml//YamlPropertySourceLoader.getFileExtensions(): yml, yamlfor (String fileExtension : loader.getFileExtensions()) {//location: [./config/, file:./, classpath:/config/, classpath:/]//name: applicationif (processed.add(fileExtension)) {//profile: null, dev//相当于对(location, fileExtension, profile)做笛卡尔积，//遍历每一种可能，然后加载//加载文件的细节在loadForFileExtension中完成loadForFileExtension(loader, location + name, "." + fileExtension,profile, filterFactory, consumer);}}}}

继续跟入 loadForFileExtension 方法，可以了解载入一个配置文件的更多细节。

回到之前的load()方法。

#ConfigFileApplicationListener.java
public void load() {this.profiles = new LinkedList<>();this.processedProfiles = new LinkedList<>();this.activatedProfiles = false;this.loaded = new LinkedHashMap<>();initializeProfiles();while (!this.profiles.isEmpty()) {Profile profile = this.profiles.poll();if (profile != null && !profile.isDefaultProfile()) {addProfileToEnvironment(profile.getName());}load(profile, this::getPositiveProfileFilter,addToLoaded(MutablePropertySources::addLast, false));this.processedProfiles.add(profile);}resetEnvironmentProfiles(this.processedProfiles);load(null, this::getNegativeProfileFilter,addToLoaded(MutablePropertySources::addFirst, true));//跟入addLoadedPropertySources();}

#ConfigFileApplicationListener.javaprivate void addLoadedPropertySources() {////destination: 进入ConfigFileApplicationListener监听器前已有的配置 //即destination中包含 systemProperties 配置源MutablePropertySources destination = this.environment.getPropertySources();//loaded: 此次监听通过扫描文件加载进来的配置源//loaded: application.yml, appcalition-dev.ymlList<MutablePropertySources> loaded = new ArrayList<>(this.loaded.values());//倒序后 loaded: application-dev.yml, application.ymlCollections.reverse(loaded);String lastAdded = null;Set<String> added = new HashSet<>();//先处理 application-dev.ymlfor (MutablePropertySources sources : loaded) {for (PropertySource<?> source : sources) {if (added.add(source.getName())) {//第一次进入: lastAdded:null//跟入addLoadedPropertySource(destination, lastAdded, source);//第一次遍历结束: lastAdded: application-devlastAdded = source.getName();}}}}private void addLoadedPropertySource(MutablePropertySources destination,String lastAdded, PropertySource<?> source) {if (lastAdded == null) {if (destination.contains(DEFAULT_PROPERTIES)) {destination.addBefore(DEFAULT_PROPERTIES, source);}else {//第一次进入: 把application-dev.yml至于最低优先级destination.addLast(source);}}else {//第二次进入://让 application.yml 优先级比 application-dev.yml 低destination.addAfter(lastAdded, source);}}

执行后得到各自的优先级，如下图：

systemProperties优先级高，解析器会优先使用 systemProperties中的 server.port 配置项即 5555 所以最终Tomcat 启动端口是 5555

从中也可以看出，如果application.yml 和 application-dev.yml中有相同的配置项，会优先采用application-dev.yml中的配置项。

参考这个:
https://www.cnblogs.com/tanliwei/p/9304072.html