Spring Boot 属性加载原理解析

爱被打了一巴掌 2024-03-16 18:00 92阅读 0赞

> 基于Spring Boot 3.1.0 系列文章
> 
> 1.  [Spring Boot 源码阅读初始化环境搭建][Spring Boot]
> 2.  [Spring Boot 框架整体启动流程详解][Spring Boot 1]
> 3.  [Spring Boot 系统初始化器详解][Spring Boot 2]
> 4.  [Spring Boot 监听器详解][Spring Boot 3]
> 5.  [Spring Boot banner详解][Spring Boot banner]
> 6.  [Spring Boot 属性配置解析][Spring Boot 4]
> 7.  [Spring Boot 属性加载原理解析][Spring Boot 5]

在《[Spring Boot 框架整体启动流程详解][Spring Boot 1]》中，我们了解到有一步是准备环境prepareEnvironment，属性加载就是在这一步开始的。

private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
    		DefaultBootstrapContext bootstrapContext, ApplicationArguments applicationArguments) {
        
    	//创建并配置环境
    	ConfigurableEnvironment environment = getOrCreateEnvironment();
    	//配置环境，如果需要转换服务，添加ApplicationConversionService，另外委托给了configurePropertySources（属性源）和configureProfiles（配置文件），子类可以覆盖该方法或分别覆盖两者进行细粒度控制
    	configureEnvironment(environment, applicationArguments.getSourceArgs());
    	//将ConfigurationPropertySource支持附加到指定的环境
    	ConfigurationPropertySources.attach(environment);
    	//调用environmentPrepared方法
    	listeners.environmentPrepared(bootstrapContext, environment);
    	//将defaultProperties属性源移动到指定配置环境的最后
    	DefaultPropertiesPropertySource.moveToEnd(environment);
    	Assert.state(!environment.containsProperty("spring.main.environment-prefix"),
    			"Environment prefix cannot be set via properties.");
    			//绑定环境到SpringApplication
    	bindToSpringApplication(environment);
    	//非自定义环境配置，就将其转换为标准类型
    	if (!this.isCustomEnvironment) {
        
    		EnvironmentConverter environmentConverter = new EnvironmentConverter(getClassLoader());
    		environment = environmentConverter.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
    	}
    	//重新将ConfigurationPropertySource支持附加到指定的环境
    	ConfigurationPropertySources.attach(environment);
    	return environment;
    }

进入`getOrCreateEnvironment()`

private ConfigurableEnvironment getOrCreateEnvironment() {
        
    //判断environment 是否为null，不为null使用environment
    	if (this.environment != null) {
        
    		return this.environment;
    	}
    	//根据web应用程序类型，通过applicationContextFactory创建environment
    	ConfigurableEnvironment environment = this.applicationContextFactory.createEnvironment(this.webApplicationType);
    	//如果environment为null，并且applicationContextFactory不是用的默认ApplicationContextFactory
    	if (environment == null && this.applicationContextFactory != ApplicationContextFactory.DEFAULT) {
        
    	//使用默认的ApplicationContextFactory创建environment
    		environment = ApplicationContextFactory.DEFAULT.createEnvironment(this.webApplicationType);
    	}
    	//如果不为null返回environment，否则只显示创建一个ApplicationEnvironment
    	return (environment != null) ? environment : new ApplicationEnvironment();
    }

`this.applicationContextFactory` 由于没有显示设置，使用的是默认的ApplicationContextFactory  
`private ApplicationContextFactory applicationContextFactory = ApplicationContextFactory.DEFAULT;`  
`ApplicationContextFactory DEFAULT = new DefaultApplicationContextFactory();`

进入`createEnvironment(this.webApplicationType)`中：

public ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {
        
    	return getFromSpringFactories(webApplicationType, ApplicationContextFactory::createEnvironment, null);
    }

进入`getFromSpringFactories`中：

private <T> T getFromSpringFactories(WebApplicationType webApplicationType,
    		BiFunction<ApplicationContextFactory, WebApplicationType, T> action, Supplier<T> defaultResult) {
        
    		//循环获取ApplicationContextFactory类型的实例
    	for (ApplicationContextFactory candidate : SpringFactoriesLoader.loadFactories(ApplicationContextFactory.class,
    			getClass().getClassLoader())) {
        
    			//调用实例的createEnvironment方法
    		T result = action.apply(candidate, webApplicationType);
    		if (result != null) {
        
    			return result;
    		}
    	}
    	return (defaultResult != null) ? defaultResult.get() : null;
    }

`SpringFactoriesLoader.loadFactories(ApplicationContextFactory.class, getClass().getClassLoader())` 从`META-INF/spring.factories`中获取并实例化ApplicationContextFactory实例，Spring Boot定义了`ReactiveWebServerApplicationContextFactory` 和 `ServletWebServerApplicationContextFactory`，所以在这里会分别去调用其中的`createEnvironment`方法，由于这边是web环境，进入ServletWebServerApplicationContextFactory的createEnvironment中。

public ConfigurableEnvironment createEnvironment(WebApplicationType webApplicationType) {
        
    //不是Web Servlet环境的话返回null，是的话创建一个ApplicationServletEnvironment
    	return (webApplicationType != WebApplicationType.SERVLET) ? null : new ApplicationServletEnvironment();
    }

进入ApplicationServletEnvironment类中，其继承了StandardServletEnvironment，StandardServletEnvironment类继承了StandardEnvironment并实现了ConfigurableWebEnvironment接口，StandardEnvironment继承了AbstractEnvironment  
![在这里插入图片描述][f3a859d9992543689a5230ab70113cce.png]  
在创建ApplicationServletEnvironment的时候，会先创建父类的构造器，所以会先执行AbstractEnvironment的构造器,AbstractEnvironment是Environment的抽象基类

public AbstractEnvironment() {
        
    	this(new MutablePropertySources());
    }

MutablePropertySources 是PropertySources接口的默认实现，PropertySources是属性配置源接口，描述了如何获取属性值。

这里再调用了当前类的有参构造器。

protected AbstractEnvironment(MutablePropertySources propertySources) {
        
    	this.propertySources = propertySources;
    	//创建配置解析器
    	this.propertyResolver = createPropertyResolver(propertySources);
    	//调用自定义配置源，具体由子类实现
    	customizePropertySources(propertySources);
    }
    
    protected void customizePropertySources(MutablePropertySources propertySources) {
        
    }

这里就调用到了`StandardServletEnvironment`的`customizePropertySources`中：

protected void customizePropertySources(MutablePropertySources propertySources) {
        
    	propertySources.addLast(new StubPropertySource(SERVLET_CONFIG_PROPERTY_SOURCE_NAME));
    	propertySources.addLast(new StubPropertySource(SERVLET_CONTEXT_PROPERTY_SOURCE_NAME));
    	if (jndiPresent && JndiLocatorDelegate.isDefaultJndiEnvironmentAvailable()) {
        
    		propertySources.addLast(new JndiPropertySource(JNDI_PROPERTY_SOURCE_NAME));
    	}
    	super.customizePropertySources(propertySources);
    }

在这里添加了关于`ServletConfig、ServletContext、JNDI`的配置源  
![在这里插入图片描述][b665b65ee04c41cfa1eeb8ca0b92ac37.png]  
在该方法的最后，又调用到了父类`StandardEnvironment`的`customizePropertySources`中：

protected void customizePropertySources(MutablePropertySources propertySources) {
        
    	propertySources.addLast(
    			new PropertiesPropertySource(SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME, getSystemProperties()));
    	propertySources.addLast(
    			new SystemEnvironmentPropertySource(SYSTEM_ENVIRONMENT_PROPERTY_SOURCE_NAME, getSystemEnvironment()));
    }

在这里添加了`Java System属性、操作系统环境变量`两个配置源  
![在这里插入图片描述][0a29ce5bca024905b3b874d43197ce11.png]  
到此为止已经添加了4个配置源，`由于这里不是JNDI环境，没有添加JNDI的配置源`，这里执行结束后返回到SpringApplication的getOrCreateEnvironment()处  
![在这里插入图片描述][d4e5fb87de9e4bdea0adc1008b824a81.png]  
接着进入`configureEnvironment(environment, applicationArguments.getSourceArgs())`中

protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
        
    	//这里用于添加转换服务
    	if (this.addConversionService) {
        
    		environment.setConversionService(new ApplicationConversionService());
    	}
    	//这里也是设置配置源，后面详解
    	configurePropertySources(environment, args);
    	//设置激活的配置文件
    	configureProfiles(environment, args);
    }

进入`configurePropertySources(environment, args)`中

protected void configurePropertySources(ConfigurableEnvironment environment, String[] args) {
        
    //获取环境中已有的配置源
    	MutablePropertySources sources = environment.getPropertySources();
    	//默认配置不为空，则添加到配置源中，defaultProperties通过springApplication.setDefaultProperties(properties) 配置
    	if (!CollectionUtils.isEmpty(this.defaultProperties)) {
        
    	//addOrMerge会判断已有的配置源中是否已经存在了defaultProperties，来判断是合并还是直接添加
    		DefaultPropertiesPropertySource.addOrMerge(this.defaultProperties, sources);
    	}
    	//判断是否有命令行参数，addCommandLineProperties表示是否允许添加命令行配置，默认为true，可通过setAddCommandLineProperties配置
    	if (this.addCommandLineProperties && args.length > 0) {
        
    	//命令行配置源名称
    		String name = CommandLinePropertySource.COMMAND_LINE_PROPERTY_SOURCE_NAME;
    		//已有配置源中是否包含命令行配置源名称
    		if (sources.contains(name)) {
        
    			PropertySource<?> source = sources.get(name);
    			CompositePropertySource composite = new CompositePropertySource(name);
    			//创建一个具有新名称的组合配置源
    			composite
    				.addPropertySource(new SimpleCommandLinePropertySource("springApplicationCommandLineArgs", args));
    			composite.addPropertySource(source);
    			//使用新的替换原来的配置源
    			sources.replace(name, composite);
    		}
    		else {
        
    			//不包含就添加到已有源的最前面
    			sources.addFirst(new SimpleCommandLinePropertySource(args));
    		}
    	}
    }

`SimpleCommandLinePropertySource` 用于解析命令行参数并填充到CommandLineArgs中，解析规则为：

> –optName\[=optValue\]  
> 必须以“–”为前缀，并且可以指定值，也可以不指定值。如果指定了值，则名称和值必须用等号（“=”）分隔，不带空格。该值可以是空字符串（可选）。  
> 有效示例有：  
> –foo  
> –foo=  
> –foo=“”  
> –foo=bar  
> –foo=“bar then baz”  
> –foo=bar,baz,biz  
> 无效示例：  
> \-foo  
> –foo bar  
> –foo = bar  
> –foo=bar --foo=baz --foo=biz

添加完命令行配置源有，进入`configureProfiles(environment, args)`中，开始设置激活的配置文件：

protected void configureProfiles(ConfigurableEnvironment environment, String[] args) {
        
    }

这是一个空的protected方法，可见需要子类去实现，这边没有SpringApplication的子类，也就不会在这里处理。  
`configureEnvironment`处理完后，进入`ConfigurationPropertySources.attach(environment)`：

public static void attach(Environment environment) {
        
    	Assert.isInstanceOf(ConfigurableEnvironment.class, environment);
    	MutablePropertySources sources = ((ConfigurableEnvironment) environment).getPropertySources();
    	PropertySource<?> attached = getAttached(sources);
    	if (attached == null || !isUsingSources(attached, sources)) {
        
    		attached = new ConfigurationPropertySourcesPropertySource(ATTACHED_PROPERTY_SOURCE_NAME,
    				new SpringConfigurationPropertySources(sources));
    	}
    	sources.remove(ATTACHED_PROPERTY_SOURCE_NAME);
    	sources.addFirst(attached);
    }

该处代码用于将`ConfigurationPropertySourcesPropertySource`类型的源添加到已有的配置源中，名称为`configurationProperties`  
这里处理完后，会调用`listeners.environmentPrepared(bootstrapContext, environment)`，通过`EventPublishingRunListener`发送ApplicationEnvironmentPreparedEvent事件，这块前面我们已经多次讲到过，这里不再复述，我们进入`EnvironmentPostProcessorApplicationListener`，其中的`onApplicationEvent`在收到ApplicationEnvironmentPreparedEvent事件后，执行`onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event)`

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

getEnvironmentPostProcessors(application.getResourceLoader(), event.getBootstrapContext()) 会获取所有的`EnvironmentPostProcessor`实例，如根据本系列文章的Demo获取到的实例有：

![在这里插入图片描述][4480b16559b54bf8992c5e6178774589.png]  
我们主要关注如下几个，其他的忽略：

*  `RandomValuePropertySourceEnvironmentPostProcessor`： 添加RandomValuePropertySource 配置源，用来解析`RandomValuePropertySource的随机值属性`
 *  `SystemEnvironmentPropertySourceEnvironmentPostProcessor`：将原来的SystemEnvironmentPropertySource替换为OriginAwareSystemEnvironmentPropertySource，以便能够跟踪每个属性的SystemEnvironmentOrigin
 *  `SpringApplicationJsonEnvironmentPostProcessor`：添加`嵌入在环境变量或系统属性中的SPRING_APPLICATION_JSON 的属性`
 *  `CloudFoundryVcapEnvironmentPostProcessor`：如果是Cloud Foundry平台，添加Cloud Foundry相关的配置源
 *  `ConfigDataEnvironmentPostProcessor`：添加application.yml等配置源
 *  `DevToolsHomePropertiesPostProcessor`：添加`Devtools 全局配置`的配置源

另外`@PropertySource注解配置`的加载是在`刷新上下文`中的`ConfigurationClassPostProcessor`类中处理，具体代码可见`ConfigurationClassParser`：  
![在这里插入图片描述][b352627cf2b44229b79029ee71417c1e.png]  
17种属性配置的加载基本都在这里了，最后总结一下

## 总结 ##

### ![在这里插入图片描述][d46bb560ee60435ba78005f4afda73b8.jpeg] ###

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[Spring Boot]: https://itsaysay.blog.csdn.net/article/details/129665897
[Spring Boot 1]: https://itsaysay.blog.csdn.net/article/details/130981611
[Spring Boot 2]: https://itsaysay.blog.csdn.net/article/details/131034991
[Spring Boot 3]: https://itsaysay.blog.csdn.net/article/details/131073017
[Spring Boot banner]: https://itsaysay.blog.csdn.net/article/details/131116036
[Spring Boot 4]: https://itsaysay.blog.csdn.net/article/details/131178566
[Spring Boot 5]: https://itsaysay.blog.csdn.net/article/details/131205549
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[d46bb560ee60435ba78005f4afda73b8.jpeg]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/15/11fe9185d75543f9a702d294b30ef95d.png
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[PromQL 2]: https://itsaysay.blog.csdn.net/article/details/128734102
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[Prometheus 2]: https://itsaysay.blog.csdn.net/article/details/129115894
[Prometheus 3]: https://itsaysay.blog.csdn.net/article/details/128741317
[Prometheus 4]: https://itsaysay.blog.csdn.net/article/details/128748383
[Prometheus _Mysql_Mysql]: https://itsaysay.blog.csdn.net/article/details/129248268
[Grafana]: https://itsaysay.blog.csdn.net/article/details/128260639
[Grafana 1]: https://itsaysay.blog.csdn.net/article/details/128280232
[Grafana 2]: https://blog.csdn.net/weixin_40972073/article/details/128292597
[Grafana 3]: https://itsaysay.blog.csdn.net/article/details/128309734
[Grafana 4]: https://itsaysay.blog.csdn.net/article/details/128379173
[Grafana 5]: https://itsaysay.blog.csdn.net/article/details/128586826
[Grafana 6]: https://itsaysay.blog.csdn.net/article/details/128665497
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