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今天就跟大家聊聊有关Springboot中ConfigFileApplicationListener的作用是什么，可能很多人都不太了解，为了让大家更加了解，小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。
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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 postProcessors = loadPostProcessors();
postProcessors.add(this);
AnnotationAwareOrderComparator.sort(postProcessors);
for (EnvironmentPostProcessor postProcessor : postProcessors) {
postProcessor.postProcessEnvironment(event.getEnvironment(),
event.getSpringApplication());
}
}
List 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 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;
}
...看完上述内容，你们对Springboot中ConfigFileApplicationListener的作用是什么有进一步的了解吗？如果还想了解更多知识或者相关内容，请关注创新互联行业资讯频道，感谢大家的支持。
