本文从SpringBoot源码分析 配置文件的加载原理和配置文件的优先级
跟入源码之前，先提一个问题：
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，为什么通过启动参数传入的配置项会“顶掉”配置文件中的配置？
示例：
application.yml
server.port: 8888
spring.profiles.active: dev
application-dev.yml
spring.think: hello
在IDEA中使用命令行配置项
VM Options
-Dserver.port=5555
如下图：
启动结果：
Tomcat started on port(s): 5555 (http) with context path ''
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。
下面开始从main函数启动处，跟入SpringBoot源码，看看SpringBoot是如何处理的。
系统说明
JDK：1.8
SpringBoot 版本： 2.0.2.RELEASE
IDE： IntelliJ IDEA 2017
跟入源码正文
#ApplicationConfigLoadFlow.java public static void main(String[] args) { SpringApplication.run(ApplicationConfigLoadFlow.class, args); }
从SpringApplication.run 函数开始，一个方法一个方法的跟入源码。需要跟入的方法给与注释或高亮。
IDEA 快捷键：
进入方法: Ctrl + 鼠标左键
光标前进/后退： Ctrl + Shirt + 右方向键/左方向键
依次跟入源码：
#SpringApplication.java return run(new Class<?>[] { primarySource }, args)
#SpringApplication.java return new SpringApplication(primarySources).run(args);
#SpringApplication.java public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>(); configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); //跟入 ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); configureIgnoreBeanInfo(environment); configureIgnoreBeanInfo(environment);
这个方法之前的源码的从类名和源码注释上知道stopWatch用于计时，上下文context还未初始化，listeners监听器存储了EventPushlingRunListener。
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。
如下图所示。注意：配置文件中的配置还未载入，请先接着往后看。
因此，我们重新打断点跟入prepareEnvironment方法。
#SpringApplication.java private ConfigurableEnvironment prepareEnvironment( SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) { // Create and configure the environment //跟入 ConfigurableEnvironment environment = getOrCreateEnvironment(); configureEnvironment(environment, applicationArguments.getSourceArgs());
#SpringApplication.java private ConfigurableEnvironment getOrCreateEnvironment() { if (this.environment != null) { return this.environment; } if (this.webApplicationType == WebApplicationType.SERVLET) { //跟入 return new StandardServletEnvironment(); }
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 public AbstractEnvironment() { //跟入 customizePropertySources(this.propertySources); if (logger.isDebugEnabled()) { logger.debug("Initialized " + getClass().getSimpleName() + " with PropertySources " + this.propertySources); } }
#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); }
#StandardEnvironment.java protected void customizePropertySources(MutablePropertySources propertySources) { //跟入 propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties())); propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment())); }
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.java public static Properties getProperties() { SecurityManager sm = getSecurityManager(); if (sm != null) { sm.checkPropertiesAccess(); } return props;
#System.java private static Properties props; private static native Properties initProperties(Properties props);
回到StandardEnvironment类的customizePropertySources方法
#StandardEnvironment.java protected void customizePropertySources(MutablePropertySources propertySources) { //SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME: systemProperties //跟入 propertySources.addLast(new MapPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties())); propertySources.addLast(new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment())); }
#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 */ public class MutablePropertySources implements PropertySources {
问题2：
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
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.java public void environmentPrepared(ConfigurableEnvironment environment) { for (SpringApplicationRunListener listener : this.listeners) { //跟入 listener.environmentPrepared(environment); } }
#EventPublishingRunListener.java public void environmentPrepared(ConfigurableEnvironment environment) { //广播ApplicationEnvrionmentPreparedEvnet事件 //跟入 this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent( this.application, this.args, environment)); }
#SimpleApplicationEventMulticaster.java public void multicastEvent(ApplicationEvent event) { //跟入 multicastEvent(event, resolveDefaultEventType(event)); } @Override public 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);
#ConfigFileApplicationListener.java 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 ConfigFileApplicationListener postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication()); } }
#ConfigFileApplicationListener.java public 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(); }
#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(); load(profile, this::getPositiveProfileFilter, addToLoaded(MutablePropertySources::addLast, false)); this.processedProfiles.add(profile); } //跟入 load(null, this::getNegativeProfileFilter, addToLoaded(MutablePropertySources::addFirst, true)); addLoadedPropertySources(); }
#ConfigFileApplicationListener.java private 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：application Set<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); } } } //this.propertySourceLoaders: PropertiesPropertySourceLoader,YamlPropertySourceLoader for (PropertySourceLoader loader : this.propertySourceLoaders) { //PropertiesPropertySourceLoader.getFileExtensions(): properties, xml //YamlPropertySourceLoader.getFileExtensions(): yml, yaml for (String fileExtension : loader.getFileExtensions()) { //location: [./config/, file:./, classpath:/config/, classpath:/] //name: application String prefix = location + name; fileExtension = "." + 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, prefix, fileExtension, profile, filterFactory, consumer); } } }
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(); load(profile, this::getPositiveProfileFilter, addToLoaded(MutablePropertySources::addLast, false)); this.processedProfiles.add(profile); } load(null, this::getNegativeProfileFilter, addToLoaded(MutablePropertySources::addFirst, true)); //跟入 addLoadedPropertySources();
#ConfigFileApplicationListener.java private 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(); String lastAdded = null; //loaded: 此次监听通过扫描文件加载进来的配置源 //loaded: application.yml, appcalition-dev.yml List<MutablePropertySources> loaded = new ArrayList<>(this.loaded.values()); //倒序后 loaded: application-dev.yml, application.yml Collections.reverse(loaded); //先处理 application-dev.yml for (MutablePropertySources sources : loaded) { for (PropertySource<?> source : sources) { //第一次进入: lastAdded:null 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); } //第一次遍历结束: lastAdded: application-dev lastAdded = source.getName(); } } }
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：