spring boot application
spring boot默认已经配置了很多环境变量，例如，tomcat的默认端口是8080，项目的contextpath是“/”等等，spring boot允许你自定义一个application.properties文件，然后放在以下的地方，来重写spring boot的环境变量
spring对配置application.properties的加载过程：
- 服务启动调用:SpringApplication.run
- 创建默认的环境参数：ConfigurableEnvironment
- 触发事件：ApplicationEnvironmentPreparedEvent
- 完成加载
整个过程主要使用spring boot 内置的ConfigFileApplicationListener监听器监听ApplicationEnvironmentPreparedEvent事件完成对application.properties加载以及设置。
下面我们来跟踪源码，看下spring boot是怎样完成对application.properties文件的加载
- SpringApplication 入口 run：
public ConfigurableApplicationContext run(String... args) {//无关的代码暂略.......ConfigurableApplicationContext context = null;FailureAnalyzers analyzers = null;configureHeadlessProperty();//获取执行监听器实例SpringApplicationRunListeners listeners = getRunListeners(args);........//创建全局系统参数实例ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);//创建 ConfigurableEnvironment 并触发ApplicationEnvironmentPreparedEvent事件 //加载配置的核心地方，spring启动首要做的事情ConfigurableEnvironment environment = prepareEnvironment(listeners,applicationArguments);.........}
prepareEnvironment方法
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments) {// Create and configure the environment//创建一个配置环境信息，当是web环境时创建StandardServletEnvironment实例，非web环境时创建StandardEnvironment实例ConfigurableEnvironment environment = getOrCreateEnvironment();configureEnvironment(environment, applicationArguments.getSourceArgs());//核心事件触发方法，此方法执行后会执行所有监听ApplicationEnvironmentPreparedEvent事件的监听器，这里我们是跟踪application.properties文件的加载，就查看ConfigFileApplicationListener监听器都做了什么工作listeners.environmentPrepared(environment);if (!this.webEnvironment) {environment = new EnvironmentConverter(getClassLoader()).convertToStandardEnvironmentIfNecessary(environment);}return environment;}
- ConfigFileApplicationListener：
public void onApplicationEvent(ApplicationEvent event) {//从此处可以看到当事件为ApplicationEnvironmentPreparedEvent时，执行onApplicationEnvironmentPreparedEvent方法if (event instanceof ApplicationEnvironmentPreparedEvent) {onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);}if (event instanceof ApplicationPreparedEvent) {onApplicationPreparedEvent(event);}}
onApplicationEnvironmentPreparedEvent
private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {//此处通过SpringFactoriesLoader加载EnvironmentPostProcessor所有扩展 List postProcessors = loadPostProcessors();//因为此监听器同样是EnvironmentPostProcessor的扩展实例，所以在此处将自己加入集合postProcessors.add(this);AnnotationAwareOrderComparator.sort(postProcessors);//遍历所有的EnvironmentPostProcessor扩展调用postProcessEnvironment//当然我们跟踪是application.properties所以主要查看当前实例的postProcessEnvironment方法for (EnvironmentPostProcessor postProcessor : postProcessors) {postProcessor.postProcessEnvironment(event.getEnvironment(),event.getSpringApplication());}}
postProcessEnvironment
@Overridepublic void postProcessEnvironment(ConfigurableEnvironment environment,SpringApplication application) {//此处添加配置信息到environment实例中，此方法完成后就将application.properties加载到环境信息中addPropertySources(environment, application.getResourceLoader());configureIgnoreBeanInfo(environment);bindToSpringApplication(environment, application);}
addPropertySources
protected void addPropertySources(ConfigurableEnvironment environment,ResourceLoader resourceLoader) {//这里先添加一个Random名称的资源到环境信息中 RandomValuePropertySource.addToEnvironment(environment);//通过Loader加载application.properties并将信息存入环境信息中new Loader(environment, resourceLoader).load();}
load
public void load() {
//创建一个资源加载器，spring boot默认支持PropertiesPropertySourceLoader，YamlPropertySourceLoader两种配置文件的加载this.propertiesLoader = new PropertySourcesLoader();this.activatedProfiles = false;//加载配置profile信息，默认为default..........此处省略while (!this.profiles.isEmpty()) {Profile profile = this.profiles.poll();//遍历所有查询路径，默认路径有：classpath:/,classpath:/config/,file:./,file:./config/for (String location : getSearchLocations()) {//这里不仅仅是加载application.properties，当搜索路径不是以/结束，默认认为是文件名已存在的路径if (!location.endsWith("/")) {// location is a filename already, so don't search for more// filenamesload(location, null, profile);}else {//遍历要加载的文件名集合，默认为applicationfor (String name : getSearchNames()) {load(location, name, profile);}}}this.processedProfiles.add(profile);}//将加载完成的配置信息全部保存到环境信息中共享addConfigurationProperties(this.propertiesLoader.getPropertySources());}
load
private void load(String location, String name, Profile profile) {//此处根据profile组装加载的文件名称以及资源所放置的组信息String group = "profile=" + (profile == null ? "" : profile);if (!StringUtils.hasText(name)) {// Try to load directly from the locationloadIntoGroup(group, location, profile);}else {// Also try the profile-specific section (if any) of the normal fileloadIntoGroup(group, location + name + "." + ext, profile);}}}
loadIntoGroup
private PropertySource doLoadIntoGroup(String identifier, String location,Profile profile) throws IOException {Resource resource = this.resourceLoader.getResource(location);PropertySource propertySource = null;if (resource != null && resource.exists()) {String name = "applicationConfig: [" + location + "]";String group = "applicationConfig: [" + identifier + "]";//资源加载核心方法，此处有两个实现，当后缀为，xml或者properties调用PropertiesPropertySourceLoader//当后缀为yml或者yaml时，调用YamlPropertySourceLoaderpropertySource = this.propertiesLoader.load(resource, }return propertySource;}
- PropertiesPropertySourceLoader：
@Overridepublic PropertySource load(String name, Resource resource, String profile)throws IOException {if (profile == null) {//此处调用PropertiesLoaderUtils工具类加载本地文件Properties properties = PropertiesLoaderUtils.loadProperties(resource);if (!properties.isEmpty()) {return new PropertiesPropertySource(name, properties);}}return null;}
到此application.properties就真正的加载并共享到环境信息中，供系统其它地方调用
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