筹备环境 ：
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) { // Create and configure the environment //如果以后有上下文环境信息，就获取并返回；没有就创立 //比方保留底层运行的环境变量 ConfigurableEnvironment environment = getOrCreateEnvironment(); //配置环境（拿到环境信息，命令行参数） configureEnvironment(environment, applicationArguments.getSourceArgs()); //绑定环境信息 ConfigurationPropertySources.attach(environment);//监听器调用 listener.environmentPrepared()；告诉所有的监听器以后环境筹备实现 listeners.environmentPrepared(bootstrapContext, environment);//将环境信息设置到类的最初(这个不必管) DefaultPropertiesPropertySource.moveToEnd(environment); //配置额定的Profiles，激活哪些环境(不必管) configureAdditionalProfiles(environment); //绑定工作（都是找到一些货色，把一些属性绑定到某个值外面） bindToSpringApplication(environment); //又是筹备一些环境信息 if (!this.isCustomEnvironment) { environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment, deduceEnvironmentClass()); } //筹备完了后，把环境信息再次绑定 ConfigurationPropertySources.attach(environment); return environment; }=================进入getOrCreateEnvironment()private ConfigurableEnvironment getOrCreateEnvironment() { if (this.environment != null) { return this.environment; } switch (this.webApplicationType) { case SERVLET: //如果是原生servlet编程 return new StandardServletEnvironment(); case REACTIVE: //如果是响应式编程 return new StandardReactiveWebEnvironment(); default: return new StandardEnvironment(); } }====================进入configureEnvironment()protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) { //给环境增加一些类型转换器 if (this.addConversionService) { ConversionService conversionService = ApplicationConversionService.getSharedInstance(); environment.setConversionService((ConfigurableConversionService) conversionService); } //加载(读取)内部配置源 //即读取所有的配置源的配置属性值 configurePropertySources(environment, args); //激活Profiles环境 configureProfiles(environment, args); }==========进入configurePropertySources()protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) { //获取到所有配置源 MutablePropertySources sources = environment.getPropertySources(); DefaultPropertiesPropertySource.ifNotEmpty(this.defaultProperties, sources::addLast); //命令行信息 if (this.addCommandLineProperties && args.length > 0) { String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME; if (sources.contains(name)) { PropertySource<?> source = sources.get(name); CompositePropertySource composite = new CompositePropertySource(name); composite.addPropertySource( new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args)); composite.addPropertySource(source); sources.replace(name, composite); } else { sources.addFirst(new SimpleCommandLinePropertySource(args)); } } }==============进入environmentPrepared（）void environmentPrepared(ConfigurableBootstrapContext bootstrapContext, ConfigurableEnvironment environment) { doWithListeners("spring.boot.application.environment-prepared", (listener) -> listener.environmentPrepared(bootstrapContext, environment)); }所有配置源