springboot源码学习02-springboot的准备环境方法prepareEnvironment

基于springboot2.1.8。
废话少说我们上代码：

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
			ApplicationArguments applicationArguments) {
		//创建并配置环境 下面有代码跟踪
		ConfigurableEnvironment environment = getOrCreateEnvironment();
		//配置环境 下面有代码跟踪
		configureEnvironment(environment, applicationArguments.getSourceArgs());
		//
		ConfigurationPropertySources.attach(environment);
		//激活环境准备完毕事件 遍历所有实现了SpringApplicationRunListener接口的类。其中就有EventPublishingRunListener ，而EventPublishingRunListener其实会发出事件，调用监听了本事件的ApplicationListener接口的类。
		//这里会激活几个实现ApplicationListener接口的类 比如：ConfigFileApplicationListener SpringApplicationJsonEnvironmentPostProcessor 等
		//其中ConfigFileApplicationListener就是添加名叫random的RandomValuePropertySource到名叫systemEnvironment的PropertySource后；并初始化Profiles；初始化PropertiesPropertySourceLoader和YamlPropertySourceLoader这两个加载器从file:./config/,file:./,classpath:/config/,classpath:/路径下加载配置文件，PropertiesPropertySourceLoader加载配置文件application.xml和application.properties，YamlPropertySourceLoader加载配置文件application.yml和application.yaml。目前我们之后classpath:/路径下有个application.yml配置文件，将其属性配置封装进了一个名叫applicationConfig:[classpath:/application.yml]的OriginTrackedMapPropertySource中，并将此对象放到了propertySourceList的最后
		//我们画一下方法执行流程ConfigFileApplicationListener的 onApplicationEvent方法会被事件调用，onApplicationEvent方法中 主要有两个方法：onApplicationEnvironmentPreparedEvent和onApplicationPreparedEvent。 onApplicationEnvironmentPreparedEvent -> postProcessor.postProcessEnvironment ->addPropertySources -> new Loader(environment, resourceLoader).load()
		//onApplicationEvent方法->addPostProcessors ->context.addBeanFactoryPostProcessor(new PropertySourceOrderingPostProcessor(context)); 这块就是想环境中加入了BeanFactoryPostProcessor。后期上下文刷新refresh()方法里面会调用到。
		listeners.environmentPrepared(environment);
		//生成一个binder 把环境 转换器 等绑定到一起
		bindToSpringApplication(environment);
		// 验证环境 是web环境强制转成StandardEnvironment 否则使用转换器转
		if (!this.isCustomEnvironment) {
			environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
					deduceEnvironmentClass());
		}
		//
		ConfigurationPropertySources.attach(environment);
		return environment;
	}

我们先看getOrCreateEnvironment方法，根据前面的web类型返回对应的环境对象，web类型通常为SERVLET所以返回new StandardServletEnvironment()。

private ConfigurableEnvironment getOrCreateEnvironment() {
		if (this.environment != null) {
			return this.environment;
		}
		switch (this.webApplicationType) {
		case SERVLET:
			//加载环境
			return new StandardServletEnvironment();
		case REACTIVE:
			return new StandardReactiveWebEnvironment();
		default:
			return new StandardEnvironment();
		}
	}

然后我们接着看configureEnvironment方法。上代码：

protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
		if (this.addConversionService) {
			//获得一个数据转换器conversionService 
			ConversionService conversionService = ApplicationConversionService.getSharedInstance();
			//把转换器set到环境中
			environment.setConversionService((ConfigurableConversionService) conversionService);
		}
		configurePropertySources(environment, args);
		configureProfiles(environment, args);
	}

继续分析下一个方法：

public static void attach(Environment environment) {
    // 判断environment是否是ConfigurableEnvironment的实例
    Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
    //获取PropertySources
    MutablePropertySources sources = ((ConfigurableEnvironment) environment)
            .getPropertySources();
    PropertySource<?> attached = sources.get(ATTACHED_PROPERTY_SOURCE_NAME);
    if (attached != null && attached.getSource() != sources) {
        sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
        attached = null;
    }
    if (attached == null) {
        // 将sources封装成ConfigurationPropertySourcesPropertySource对象，并把这个对象放到sources的第一位置
        sources.addFirst(new ConfigurationPropertySourcesPropertySource(
                ATTACHED_PROPERTY_SOURCE_NAME,
                new SpringConfigurationPropertySources(sources)));
    }
}