SpringBoot 扩展篇：ConfigFileApplicationListener源码解析

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已于 2024-05-03 09:46:27 修改 · 1.2k 阅读

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#spring boot #后端 #java

于 2024-05-03 09:33:24 首次发布

本文从源码角度分析Spring Boot配置文件加载原理。Spring Boot的配置文件加载由ConfigFileApplicationListener完成，加载的配置信息最终放入Environment。文中详细介绍了回调链路、环境准备事件及加载配置类的过程，还总结了配置文件加载顺序，最后提出了遗留问题。

SpringBoot 扩展篇：ConfigFileApplicationListener源码解析

1.概述

SpringBoot的配置文件加载由ConfigFileApplicationListener完成的，它会加载application.properties、application.yml等配置文件，还支持用户配置和扩展。本文从源码的角度分析它的原理。

加载完毕的配置信息最终都会放入到Environment中。

2. ConfigFileApplicationListener定义

在这里插入图片描述
ConfigFileApplicationListener定义在spring.factories中。监听器注册和执行原理参考：SpringBoot 源码解析3：事件监听器

3. ConfigFileApplicationListener回调链路

3.1 SpringApplication#run

public ConfigurableApplicationContext run(String... args) {
   
   
	StopWatch stopWatch = new StopWatch();
	stopWatch.start();
	ConfigurableApplicationContext context = null;
	configureHeadlessProperty();
	SpringApplicationRunListeners listeners = getRunListeners(args);
	listeners.starting();
	try {
   
   
		ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
		ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments);
		configureIgnoreBeanInfo(environment);
		Banner printedBanner = printBanner(environment);
		context = createApplicationContext();
		prepareContext(context, environment, listeners, applicationArguments, printedBanner);
		refreshContext(context);
		afterRefresh(context, applicationArguments);
		stopWatch.stop();
		if (this.logStartupInfo) {
   
   
			new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
		}
		listeners.started(context);
		callRunners(context, applicationArguments);
	}
	catch (Throwable ex) {
   
   
		handleRunFailure(context, ex, listeners);
		throw new IllegalStateException(ex);
	}

	try {
   
   
		listeners.running(context);
	}
	catch (Throwable ex) {
   
   
		handleRunFailure(context, ex, null);
		throw new IllegalStateException(ex);
	}
	return context;
}

这是SpringBoot启动最基础的方法，调用了prepareEnvironment。

3.2 SpringApplication#prepareEnvironment

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
		ApplicationArguments applicationArguments) {
   
   
	// Create and configure the environment
	// 创建environment对象
	ConfigurableEnvironment environment = getOrCreateEnvironment();
	// 配置环境
	configureEnvironment(environment, applicationArguments.getSourceArgs());
	ConfigurationPropertySources.attach(environment);
	// 发布监听事件
	listeners.environmentPrepared(environment);
	bindToSpringApplication(environment);
	if (!this.isCustomEnvironment) {
   
   
		environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
				deduceEnvironmentClass());
	}
	ConfigurationPropertySources.attach(environment);
	return environment;
}

getOrCreateEnvironment创建StandardServletEnvironment，所有的启动参数和配置文件信息都会保存到environment中。environment中默认创建了4个propertySource，分别用来存放系统属性和servlet属性。
configureEnvironment配置环境信息，此时配置文件还没解析。
listeners.environmentPrepared，调用监听器ConfigFileApplicationListener解析配置文件。最终回调了ConfigFileApplicationListener#onApplicationEvent，这里是解析文件的核心逻辑。

@Override
public void environmentPrepared(ConfigurableEnvironment environment) {
   
   
	this.initialMulticaster
			.multicastEvent(new ApplicationEnvironmentPreparedEvent(this.application, this.args, environment));
}

监听器发布的是ApplicationEnvironmentPreparedEvent类型的事件。

bindToSpringApplication解析完毕所有的配置文件信息之后，将spring.main.*的环境变量与当前的springApplication对象的属性绑定。比如allowBeanDefinitionOverriding配置就是在这里读取的。

3.3 配置environment

SpringApplication#configureEnvironment

protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
   
   
	if (this.addConversionService) {
   
   
		ConversionService conversionService = ApplicationConversionService.getSharedInstance();
		environment.setConversionService((ConfigurableConversionService) conversionService);
	}
	configurePropertySources(environment, args);
	configureProfiles(environment, args);
}

第二个参数args为SpringBoot启动参数。
configurePropertySources方法会将启动参数解析保存到environment中。

protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
   
   
	MutablePropertySources sources = environment.getPropertySources();
	if (this.defaultProperties != null && !this.defaultProperties.isEmpty()) {
   
   
		sources.addLast(new MapPropertySource("defaultProperties", this.defaultProperties));
	}
	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));
		}
	}
}

通过addFirst会将启动参数的属性添加到第一个PropertySources，优先级最高。

protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) {
   
   
	if (this.propertySources != null) {
   
   
		for (PropertySource<?> propertySource : this.propertySources) {
   
   
			if (logger.isTraceEnabled()) {
   
   
				logger.trace("Searching for key '" + key + "' in PropertySource '" +
						propertySource.getName() + "'");
			}
			Object value = propertySource.getProperty(key);
			if (value != null) {
   
   
				if (resolveNestedPlaceholders && value instanceof String) {
   
   
					value = resolveNestedPlaceholders((String) value);
				}
				logKeyFound(key, propertySource, value);
				return convertValueIfNecessary(value, targetValueType);
			}