Springboot之ConfigFileApplicationListener

    Springboot版本2.0.5.release。

    如下图1所示:

                                                                                     图1

    ConfigFileApplicationListener实现了ApplicationListener，所以会收到Springboot的Event事件，如下List-1所示onApplicationEvent收到ApplicationEnvironmentPreparedEvent事件后，通过onApplicationEnvironmentPreparedEvent方法，获取spring.factories中的所有EnvironmentPostProcessor，并逐个调用EnvironmentPostProcessor的postProcessEnvironment方法。

    List-1

@Override
public void onApplicationEvent(ApplicationEvent event) {
	if (event instanceof ApplicationEnvironmentPreparedEvent) {
		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) {
		postProcessor.postProcessEnvironment(event.getEnvironment(),
				event.getSpringApplication());
	}
}

List<EnvironmentPostProcessor> loadPostProcessors() {
	return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class,
			getClass().getClassLoader());
}
           

    List-1中onApplicationEnvironmentPreparedEvent方法里"postProcessors.add(this)"，把当前实例也加入其中，所以来看看ConfigFileApplicationListener的postProcessEnvironment，如下List-2所示：

    List-2

@Override
public void postProcessEnvironment(ConfigurableEnvironment environment,
		SpringApplication application) {
	addPropertySources(environment, application.getResourceLoader());
}
...
protected void addPropertySources(ConfigurableEnvironment environment,
		ResourceLoader resourceLoader) {
	RandomValuePropertySource.addToEnvironment(environment);
	new Loader(environment, resourceLoader).load();
}
           

    List-2中的Loader是个内部类，在ConfigFileApplicationListener中，Loader的构造方法如下List-3所示，从spring.factories中获得PropertySourceLoader，实现类有俩个，即PropertiesPropertySourceLoader和YamlPropertySourceLoader。

    List-3

...
Loader(ConfigurableEnvironment environment, ResourceLoader resourceLoader) {
	this.environment = environment;
	this.resourceLoader = (resourceLoader != null) ? resourceLoader
			: new DefaultResourceLoader();
	this.propertySourceLoaders = SpringFactoriesLoader.loadFactories(
			PropertySourceLoader.class, getClass().getClassLoader());
}
...
           

    List-4

# PropertySource Loaders
org.springframework.boot.env.PropertySourceLoader=\
org.springframework.boot.env.PropertiesPropertySourceLoader,\
org.springframework.boot.env.YamlPropertySourceLoader
           

    PropertiesPropertySourceLoader如下List-5，它支持的有properties和xml文件，并最终解析为Properties，封转到PropertiesPropertySource中。

    List-5

public class PropertiesPropertySourceLoader implements PropertySourceLoader {
 
    public String[] getFileExtensions() {
        return new String[]{"properties", "xml"};
    }

    public PropertySource<?> load(String name, Resource resource, String profile) throws IOException {
        if (profile == null) {
            Properties properties = PropertiesLoaderUtils.loadProperties(resource);
            if (!properties.isEmpty()) {
                return new PropertiesPropertySource(name, properties);
            }
        }
        return null;
    }
}
           

    YamlPropertySourceLoader如下List-6所示，支持的文件有yml和yaml，将yaml文件内容解析为map，之后封装到MapPropertySource。

    List-6

public class YamlPropertySourceLoader implements PropertySourceLoader {
    public String[] getFileExtensions() {
        return new String[]{"yml", "yaml"};
    }

    public PropertySource<?> load(String name, Resource resource, String profile) throws IOException {
        if (ClassUtils.isPresent("org.yaml.snakeyaml.Yaml", (ClassLoader)null)) {
            YamlPropertySourceLoader.Processor processor = new YamlPropertySourceLoader.Processor(resource, profile);
            Map<String, Object> source = processor.process();
            if (!source.isEmpty()) {
                return new MapPropertySource(name, source);
            }
        }
        return null;
	}
	...
           

    从ConfigFileApplicationListener中可以看到，Springboot通过事件触发解析配置文件的操作(如下List-7中的listeners.environmentPrepared(environment)处)，其中properties和xml文件解析到JDK的Properties中，之后加入到Springboot的evironment中；yml和yaml文件解析到JDK的map中，之后加入到evironment中。

    List-7

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,ApplicationArguments applicationArguments) {
	// Create and configure the environment
	ConfigurableEnvironment environment = getOrCreateEnvironment();
	configureEnvironment(environment, applicationArguments.getSourceArgs());
	listeners.environmentPrepared(environment);
	bindToSpringApplication(environment);
	if (!this.isCustomEnvironment) {
	environment = new EnvironmentConverter(getClassLoader())
			.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
	}
	ConfigurationPropertySources.attach(environment);
	return environment;
}
...
           

    通过上面这些步骤，Springboot将配置文件的内容全部解析到evironment中。

Reference

1. 源码https://github.com/spring-projects/spring-boot/tree/v2.0.5.RELEASE

转载于:https://my.oschina.net/u/2518341/blog/3083051