第3-1 章： EnvironmentPostProcessorApplicationListener

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李延 LV6 2021-05-20

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# 作用

evironment的后置处理器，继承于ApplicationListener，所以它是springboot启动时的一个监听器

# 继承

![image](//cdn.hiboot.cn/a22e33736d364d189f7e40faae17c22d.png)
父类为SmartApplicationListener。我们通过上一章分析，这个接口通过supportsEventType和supportsSourceType方法判断监听哪些事件。
我们看一下具体代码：

```java
	@Override
	public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) {
		return ApplicationEnvironmentPreparedEvent.class.isAssignableFrom(eventType)
				|| ApplicationPreparedEvent.class.isAssignableFrom(eventType)
				|| ApplicationFailedEvent.class.isAssignableFrom(eventType);
	}

```

所以很明显，上面的这3个事件会被监听。

# 初始化

```java
	public EnvironmentPostProcessorApplicationListener() {
		this(EnvironmentPostProcessorsFactory
				.fromSpringFactories(EnvironmentPostProcessorApplicationListener.class.getClassLoader()));
	}
static EnvironmentPostProcessorsFactory fromSpringFactories(ClassLoader classLoader) {
		return new ReflectionEnvironmentPostProcessorsFactory(
				SpringFactoriesLoader.loadFactoryNames(EnvironmentPostProcessor.class, classLoader));
	}
```

这里我们看到了熟悉的代码。发现所有的EnvironmentPostProcessor对象都是从META-INF/spring.factories文件中加载的。

# onApplicationEvent

我们都知道 监听器都是通过这个方法来接收事件的，所以我们看一下这个方法

```java

@Override
	public void onApplicationEvent(ApplicationEvent event) {
		if (event instanceof ApplicationEnvironmentPreparedEvent) {
			onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
		}
		if (event instanceof ApplicationPreparedEvent) {
			onApplicationPreparedEvent((ApplicationPreparedEvent) event);
		}
		if (event instanceof ApplicationFailedEvent) {
			onApplicationFailedEvent((ApplicationFailedEvent) event);
		}
	}

private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) {
		ConfigurableEnvironment environment = event.getEnvironment();
		SpringApplication application = event.getSpringApplication();
		for (EnvironmentPostProcessor postProcessor : getEnvironmentPostProcessors(event.getBootstrapContext())) {
			postProcessor.postProcessEnvironment(environment, application);
		}
	}

```
其实很明白，就是在环境准备完成后的ApplicationEnvironmentPreparedEvent事件中，依次调用所有的EnvironmentPostProcessor对象。

我们之后代码主要说明关于文件解析的ConfigDataEnvironmentPostProcessor。

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