基于SpringBoot的Environment源码理解实现分散配置

来源：https://www.cnblogs.com/throwable/p/9411100.html

前提

org.springframework.core.env.Environment是当前应用运行环境的公开接口，主要包括应用程序运行环境的两个关键方面：配置文件(profiles)和属性。Environment继承自接口PropertyResolver，而PropertyResolver提供了属性访问的相关方法。这篇文章从源码的角度分析Environment的存储容器和加载流程，然后基于源码的理解给出一个生产级别的扩展。

本文较长，请用一个舒服的姿势阅读。

Environment类体系

• PropertyResolver：提供属性访问功能。

• ConfigurablePropertyResolver：继承自PropertyResolver，主要提供属性类型转换(基于org.springframework.core.convert.ConversionService)功能。

• Environment：继承自PropertyResolver，提供访问和判断profiles的功能。

• ConfigurableEnvironment：继承自ConfigurablePropertyResolver和Environment，并且提供设置激活的profile和默认的profile的功能。

• ConfigurableWebEnvironment：继承自ConfigurableEnvironment，并且提供配置Servlet上下文和Servlet参数的功能。

• AbstractEnvironment：实现了ConfigurableEnvironment接口，默认属性和存储容器的定义，并且实现了ConfigurableEnvironment种的方法，并且为子类预留可覆盖了扩展方法。

• StandardEnvironment：继承自AbstractEnvironment，非Servlet(Web)环境下的标准Environment实现。

• StandardServletEnvironment：继承自StandardEnvironment，Servlet(Web)环境下的标准Environment实现。

reactive相关的暂时不研究。

Environment提供的方法

一般情况下，我们在SpringMVC项目中启用到的是StandardServletEnvironment，它的父接口问ConfigurableWebEnvironment，我们可以查看此接口提供的方法：

Environment的存储容器

Environment的静态属性和存储容器都是在AbstractEnvironment中定义的，ConfigurableWebEnvironment接口提供的 getPropertySources() 方法可以获取到返回的MutablePropertySources实例，然后添加额外的PropertySource。实际上，Environment的存储容器就是org.springframework.core.env.PropertySource的子类集合，AbstractEnvironment中使用的实例是org.springframework.core.env.MutablePropertySources，下面看下PropertySource的源码：

public abstract class PropertySource<T> {

	protected final Log logger = LogFactory.getLog(getClass());

	protected final String name;

	protected final T source;

    public PropertySource(String name, T source) {
		Assert.hasText(name, "Property source name must contain at least one character");
		Assert.notNull(source, "Property source must not be null");
		this.name = name;
		this.source = source;
	}

    @SuppressWarnings("unchecked")
	public PropertySource(String name) {
		this(name, (T) new Object());
	}

    public String getName() {
		return this.name;
	}

	public T getSource() {
		return this.source;
	}

	public boolean containsProperty(String name) {
		return (getProperty(name) != null);
	}

	@Nullable
	public abstract Object getProperty(String name);

 	@Override
	public boolean equals(Object obj) {
		return (this == obj || (obj instanceof PropertySource &&
				ObjectUtils.nullSafeEquals(this.name, ((PropertySource<?>) obj).name)));
	}

	@Override
	public int hashCode() {
		return ObjectUtils.nullSafeHashCode(this.name);
	}
//省略其他方法和内部类的源码
}

源码相对简单，预留了一个 getProperty 抽象方法给子类实现， 重点需要关注的是覆写了的 equals 和 hashCode 方法，实际上只和 name 属性相关，这一点很重要，说明一个PropertySource实例绑定到一个唯一的name，这个name有点像HashMap里面的key ，部分移除、判断方法都是基于name属性。PropertySource的最常用子类是MapPropertySource、PropertiesPropertySource、ResourcePropertySource、StubPropertySource、ComparisonPropertySource：

• MapPropertySource：source指定为Map实例的PropertySource实现。

• PropertiesPropertySource：source指定为Map实例的PropertySource实现，内部的Map实例由Properties实例转换而来。

• ResourcePropertySource：继承自PropertiesPropertySource，source指定为通过Resource实例转化为Properties再转换为Map实例。

• StubPropertySource：PropertySource的一个内部类，source设置为null，实际上就是空实现。

• ComparisonPropertySource：继承自ComparisonPropertySource，所有属性访问方法强制抛出异常，作用就是一个不可访问属性的空实现。

AbstractEnvironment中的属性定义：

public static final String IGNORE_GETENV_PROPERTY_NAME = "spring.getenv.ignore";
public static final String ACTIVE_PROFILES_PROPERTY_NAME = "spring.profiles.active";
public static final String DEFAULT_PROFILES_PROPERTY_NAME = "spring.profiles.default";
protected static final String RESERVED_DEFAULT_PROFILE_NAME = "default";

private final Set<String> activeProfiles = new LinkedHashSet<>();

private final Set<String> defaultProfiles = new LinkedHashSet<>(getReservedDefaultProfiles());

private final MutablePropertySources propertySources = new MutablePropertySources(this.logger);

private final ConfigurablePropertyResolver propertyResolver = new PropertySourcesPropertyResolver(this.propertySources);

上面的propertySources(MutablePropertySources类型)属性就是用来存放PropertySource列表的，PropertySourcesPropertyResolver是ConfigurablePropertyResolver的实现，默认的profile就是字符串default。MutablePropertySources的内部属性如下：

Copy

没错，这个就是最底层的存储容器，也就是环境属性都是存放在一个CopyOnWriteArrayList<PropertySource<?>>实例中。MutablePropertySources是PropertySources的子类，它提供了 get(String name) 、 addFirst 、 addLast 、 addBefore 、 addAfter 、 remove 、 replace 等便捷方法，方便操作propertySourceList集合的元素，这里挑选 addBefore 的源码分析：

public void addBefore(String relativePropertySourceName, PropertySource<?> propertySource) {
	if (logger.isDebugEnabled()) {
		logger.debug("Adding PropertySource '" + propertySource.getName() +
					"' with search precedence immediately higher than '" + relativePropertySourceName + "'");
	}
    //前一个PropertySource的name指定为relativePropertySourceName时候必须和添加的PropertySource的name属性不相同
	assertLegalRelativeAddition(relativePropertySourceName, propertySource);
    //尝试移除同名的PropertySource
	removeIfPresent(propertySource);
    //获取前一个PropertySource在CopyOnWriteArrayList中的索引
	int index = assertPresentAndGetIndex(relativePropertySourceName);
    //添加当前传入的PropertySource到指定前一个PropertySource的索引，相当于relativePropertySourceName对应的PropertySource后移到原来索引值+1的位置
	addAtIndex(index, propertySource);
}

protected void assertLegalRelativeAddition(String relativePropertySourceName, PropertySource<?> propertySource) {
	String newPropertySourceName = propertySource.getName();
	if (relativePropertySourceName.equals(newPropertySourceName)) {
		throw new IllegalArgumentException(
					"PropertySource named '" + newPropertySourceName + "' cannot be added relative to itself");
	}
}

protected void removeIfPresent(PropertySource<?> propertySource) {
	this.propertySourceList.remove(propertySource);
}

private int assertPresentAndGetIndex(String name) {
	int index = this.propertySourceList.indexOf(PropertySource.named(name));
	if (index == -1) {
		throw new IllegalArgumentException("PropertySource named '" + name + "' does not exist");
	}
	return index;
}

private void addAtIndex(int index, PropertySource<?> propertySource) {
    //注意，这里会再次尝试移除同名的PropertySource
	removeIfPresent(propertySource);
	this.propertySourceList.add(index, propertySource);
}

大多数PropertySource子类的修饰符都是public，可以直接使用，这里写个小demo：

MutablePropertySources mutablePropertySources = new MutablePropertySources();
Map<String, Object> map = new HashMap<>(8);
map.put("name", "throwable");
map.put("age", 25);
MapPropertySource mapPropertySource = new MapPropertySource("map", map);
mutablePropertySources.addLast(mapPropertySource);
Properties properties = new Properties();
PropertiesPropertySource propertiesPropertySource = new PropertiesPropertySource("prop", properties);
properties.put("name", "doge");
properties.put("gourp", "group-a");
mutablePropertySources.addBefore("map", propertiesPropertySource);
System.out.println(mutablePropertySources);

Environment加载过程源码分析

Environment加载的源码位于 SpringApplication#prepareEnvironment ：

private ConfigurableEnvironment prepareEnvironment(
			SpringApplicationRunListeners listeners,
			ApplicationArguments applicationArguments) {
		// Create and configure the environment
        //创建ConfigurableEnvironment实例
		ConfigurableEnvironment environment = getOrCreateEnvironment();
        //启动参数绑定到ConfigurableEnvironment中
		configureEnvironment(environment, applicationArguments.getSourceArgs());
        //发布ConfigurableEnvironment准备完毕事件
		listeners.environmentPrepared(environment);
        //绑定ConfigurableEnvironment到当前的SpringApplication实例中
		bindToSpringApplication(environment);
        //这一步是非SpringMVC项目的处理，暂时忽略
		if (this.webApplicationType == WebApplicationType.NONE) {
			environment = new EnvironmentConverter(getClassLoader())
					.convertToStandardEnvironmentIfNecessary(environment);
		}
        //绑定ConfigurationPropertySourcesPropertySource到ConfigurableEnvironment中，name为configurationProperties，实例是SpringConfigurationPropertySources，属性实际是ConfigurableEnvironment中的MutablePropertySources
		ConfigurationPropertySources.attach(environment);
		return environment;
	}

这里重点看下 getOrCreateEnvironment 方法：

private ConfigurableEnvironment getOrCreateEnvironment() {
	if (this.environment != null) {
		return this.environment;
	}
    //在SpringMVC项目，ConfigurableEnvironment接口的实例就是新建的StandardServletEnvironment实例
	if (this.webApplicationType == WebApplicationType.SERVLET) {
		return new StandardServletEnvironment();
	}
	return new StandardEnvironment();
}
//REACTIVE_WEB_ENVIRONMENT_CLASS=org.springframework.web.reactive.DispatcherHandler
//MVC_WEB_ENVIRONMENT_CLASS=org.springframework.web.servlet.DispatcherServlet
//MVC_WEB_ENVIRONMENT_CLASS={"javax.servlet.Servlet","org.springframework.web.context.ConfigurableWebApplicationContext"}
//这里，默认就是WebApplicationType.SERVLET
private WebApplicationType deduceWebApplicationType() {
	if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
		&& !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
		return WebApplicationType.REACTIVE;
	}
	for (String className : WEB_ENVIRONMENT_CLASSES) {
		if (!ClassUtils.isPresent(className, null)) {
			return WebApplicationType.NONE;
		}
	}
	return WebApplicationType.SERVLET;
}

还有一个地方要重点关注：发布ConfigurableEnvironment准备完毕事件 listeners.environmentPrepared(environment) ，实际上这里用到了同步的EventBus，事件的监听者是ConfigFileApplicationListener，具体处理逻辑是 onApplicationEnvironmentPreparedEvent 方法：

private void onApplicationEnvironmentPreparedEvent(
			ApplicationEnvironmentPreparedEvent event) {
	List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
	postProcessors.add(this);
	AnnotationAwareOrderComparator.sort(postProcessors);
    //遍历所有的EnvironmentPostProcessor对Environment实例进行处理
	for (EnvironmentPostProcessor postProcessor : postProcessors) {
		postProcessor.postProcessEnvironment(event.getEnvironment(),
					event.getSpringApplication());
	}
}

//从spring.factories文件中加载，一共有四个实例
//ConfigFileApplicationListener
//CloudFoundryVcapEnvironmentPostProcessor
//SpringApplicationJsonEnvironmentPostProcessor
//SystemEnvironmentPropertySourceEnvironmentPostProcessor
List<EnvironmentPostProcessor> loadPostProcessors() {
	return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class,
				getClass().getClassLoader());
}

实际上，处理工作大部分都在ConfigFileApplicationListener中，见它的 postProcessEnvironment 方法：

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();
}

主要的配置环境加载逻辑在内部类Loader，Loader会匹配多个路径下的文件把属性加载到ConfigurableEnvironment中，加载器主要是PropertySourceLoader的实例，例如我们用到application-${profile}.yaml文件做应用主配置文件，使用的是YamlPropertySourceLoader，这个时候activeProfiles也会被设置到ConfigurableEnvironment中。加载完毕之后，ConfigurableEnvironment中基本包含了所有需要加载的属性(activeProfiles是这个时候被写入ConfigurableEnvironment)。值得注意的是，几乎所有属性都是key-value形式存储，如xxx.yyyy.zzzzz=value、xxx.yyyy[0].zzzzz=value-1、xxx.yyyy[1].zzzzz=value-2。 Loader 中的逻辑相对复杂，有比较多的遍历和过滤条件，这里不做展开。

Environment属性访问源码分析

上文提到过，都是委托到PropertySourcesPropertyResolver，先看它的构造函数：

@Nullable
private final PropertySources propertySources;

public PropertySourcesPropertyResolver(@Nullable PropertySources propertySources) {
		this.propertySources = propertySources;
	}

只依赖于一个PropertySources实例，在SpringBoot的SpringMVC项目中就是MutablePropertySources的实例。重点分析一下最复杂的一个方法：

protected <T> T getProperty(String key, Class<T> targetValueType, boolean resolveNestedPlaceholders) {
	if (this.propertySources != null) {
        //遍历所有的PropertySource
		for (PropertySource<?> propertySource : this.propertySources) {
			if (logger.isTraceEnabled()) {
				logger.trace("Searching for key '" + key + "' in PropertySource '" +
							propertySource.getName() + "'");
			}
			Object value = propertySource.getProperty(key);
            //选用第一个不为null的匹配key的属性值
			if (value != null) {
				if (resolveNestedPlaceholders && value instanceof String) {
                    //处理属性占位符，如${server.port}，底层委托到PropertyPlaceholderHelper完成
					value = resolveNestedPlaceholders((String) value);
				}
				logKeyFound(key, propertySource, value);
                //如果需要的话，进行一次类型转换，底层委托到DefaultConversionService完成
				return convertValueIfNecessary(value, targetValueType);
			}
		}
	}
	if (logger.isDebugEnabled()) {
		logger.debug("Could not find key '" + key + "' in any property source");
	}
	return null;
}

这里的源码告诉我们，如果出现多个PropertySource中存在同名的key，返回的是第一个PropertySource对应key的属性值的处理结果，因此我们如果需要自定义一些环境属性，需要十分清楚各个PropertySource的顺序。

扩展-实现分散配置

在不使用SpringCloud配置中心的情况下，一般的SpringBoot项目的配置文件如下：

- src
 - main
  - resources
   - application-prod.yaml
   - application-dev.yaml
   - application-test.yaml

随着项目发展，配置项越来越多，导致了application-${profile}.yaml迅速膨胀，大的配置文件甚至超过一千行，为了简化和划分不同功能的配置，可以考虑把配置文件拆分如下：

- src
 - main
  - resources
   - profiles
     - dev
       - business.yaml
       - mq.json
       - datasource.properties
     - prod
       - business.yaml
       - mq.json
       - datasource.properties
     - test  
       - business.yaml
       - mq.json  
       - datasource.properties
   - application-prod.yaml
   - application-dev.yaml
   - application-test.yaml

外层的application-${profile}.yaml只留下项目的核心配置如server.port等，其他配置打散放在/profiles/${profile}/各自的配置文件中。实现方式是：依据当前配置的spring.profiles.active属性，读取类路径中指定文件夹下的配置文件中，加载到Environment中，需要注意这一个加载步骤必须在Spring刷新上下文方法最后一步 finishRefresh 之前完成(这一点原因可以参考之前在个人博客写过的SpringBoot刷新上下文源码的分析)，否则有可能会影响到占位符属性的自动装配(例如使用了@Value("${filed}"))。

先定义一个属性探索者接口：

public interface PropertySourceDetector {

    /**
     * 获取支持的文件后缀数组
     *
     * @return String[]
     */
    String[] getFileExtensions();

    /**
     * 加载目标文件属性到环境中
     *
     * @param environment environment
     * @param name        name
     * @param resource    resource
     * @throws IOException IOException
     */
    void load(ConfigurableEnvironment environment, String name, Resource resource) throws IOException;
}

然后需要一个抽象属性探索者把Resource转换为字符串，额外提供Map的缩进、添加PropertySource到Environment等方法：

public abstract class AbstractPropertySourceDetector implements PropertySourceDetector {

    private static final String SERVLET_ENVIRONMENT_CLASS = "org.springframework.web."
            + "context.support.StandardServletEnvironment";

    public boolean support(String fileExtension) {
        String[] fileExtensions = getFileExtensions();
        return null != fileExtensions &&
                Arrays.stream(fileExtensions).anyMatch(extension -> extension.equals(fileExtension));
    }

    private String findPropertySource(MutablePropertySources sources) {
        if (ClassUtils.isPresent(SERVLET_ENVIRONMENT_CLASS, null) && sources
                .contains(StandardServletEnvironment.JNDI_PROPERTY_SOURCE_NAME)) {
            return StandardServletEnvironment.JNDI_PROPERTY_SOURCE_NAME;
        }
        return StandardEnvironment.SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME;
    }

    protected void addPropertySource(ConfigurableEnvironment environment, PropertySource<?> source) {
        MutablePropertySources sources = environment.getPropertySources();
        String name = findPropertySource(sources);
        if (sources.contains(name)) {
            sources.addBefore(name, source);
        } else {
            sources.addFirst(source);
        }
    }

    protected Map<String, Object> flatten(Map<String, Object> map) {
        Map<String, Object> result = new LinkedHashMap<>();
        flatten(null, result, map);
        return result;
    }

    private void flatten(String prefix, Map<String, Object> result, Map<String, Object> map) {
        String namePrefix = (prefix != null ? prefix + "." : "");
        map.forEach((key, value) -> extract(namePrefix + key, result, value));
    }

    @SuppressWarnings("unchecked")
    private void extract(String name, Map<String, Object> result, Object value) {
        if (value instanceof Map) {
            flatten(name, result, (Map<String, Object>) value);
        } else if (value instanceof Collection) {
            int index = 0;
            for (Object object : (Collection<Object>) value) {
                extract(name + "[" + index + "]", result, object);
                index++;
            }
        } else {
            result.put(name, value);
        }
    }

    protected String getContentStringFromResource(Resource resource) throws IOException {
        return StreamUtils.copyToString(resource.getInputStream(), Charset.forName("UTF-8"));
    }
}

上面的方法参考SpringApplicationJsonEnvironmentPostProcessor，然后编写各种类型配置属性探索者的实现：

//Json
@Slf4j
public class JsonPropertySourceDetector extends AbstractPropertySourceDetector {

    private static final JsonParser JSON_PARSER = JsonParserFactory.getJsonParser();

    @Override
    public String[] getFileExtensions() {
        return new String[]{"json"};
    }

    @Override
    public void load(ConfigurableEnvironment environment, String name, Resource resource) throws IOException {
        try {
            Map<String, Object> map = JSON_PARSER.parseMap(getContentStringFromResource(resource));
            Map<String, Object> target = flatten(map);
            addPropertySource(environment, new MapPropertySource(name, target));
        } catch (Exception e) {
            log.warn("加载Json文件属性到环境变量失败,name = {},resource = {}", name, resource);
        }
    }
}
//Properties
public class PropertiesPropertySourceDetector extends AbstractPropertySourceDetector {

    @Override
    public String[] getFileExtensions() {
        return new String[]{"properties", "conf"};
    }

    @SuppressWarnings("unchecked")
    @Override
    public void load(ConfigurableEnvironment environment, String name, Resource resource) throws IOException {
        Map map = PropertiesLoaderUtils.loadProperties(resource);
        addPropertySource(environment, new MapPropertySource(name, map));
    }
}
//Yaml
@Slf4j
public class YamlPropertySourceDetector extends AbstractPropertySourceDetector {

    private static final JsonParser YAML_PARSER = new YamlJsonParser();

    @Override
    public String[] getFileExtensions() {
        return new String[]{"yaml", "yml"};
    }

    @Override
    public void load(ConfigurableEnvironment environment, String name, Resource resource) throws IOException {
        try {
            Map<String, Object> map = YAML_PARSER.parseMap(getContentStringFromResource(resource));
            Map<String, Object> target = flatten(map);
            addPropertySource(environment, new MapPropertySource(name, target));
        } catch (Exception e) {
            log.warn("加载Yaml文件属性到环境变量失败,name = {},resource = {}", name, resource);
        }
    }
}

子类的全部PropertySource都是MapPropertySource，name为文件的名称，所有PropertySource都用 addBefore 方法插入到 systemProperties 的前面，主要是为了提高匹配属性的优先级。接着需要定义一个属性探索者的合成类用来装载所有的子类：

public class PropertySourceDetectorComposite implements PropertySourceDetector {

    private static final String DEFAULT_SUFFIX = "properties";
    private final List<AbstractPropertySourceDetector> propertySourceDetectors = new ArrayList<>();

    public void addPropertySourceDetector(AbstractPropertySourceDetector sourceDetector) {
        propertySourceDetectors.add(sourceDetector);
    }

    public void addPropertySourceDetectors(List<AbstractPropertySourceDetector> sourceDetectors) {
        propertySourceDetectors.addAll(sourceDetectors);
    }

    public List<AbstractPropertySourceDetector> getPropertySourceDetectors() {
        return Collections.unmodifiableList(propertySourceDetectors);
    }

    @Override
    public String[] getFileExtensions() {
        List<String> fileExtensions = new ArrayList<>(8);
        for (AbstractPropertySourceDetector propertySourceDetector : propertySourceDetectors) {
            fileExtensions.addAll(Arrays.asList(propertySourceDetector.getFileExtensions()));
        }
        return fileExtensions.toArray(new String[0]);
    }

    @Override
    public void load(ConfigurableEnvironment environment, String name, Resource resource) throws IOException {
        if (resource.isFile()) {
            String fileName = resource.getFile().getName();
            int index = fileName.lastIndexOf(".");
            String suffix;
            if (-1 == index) {
                //如果文件没有后缀,当作properties处理
                suffix = DEFAULT_SUFFIX;
            } else {
                suffix = fileName.substring(index + 1);
            }
            for (AbstractPropertySourceDetector propertySourceDetector : propertySourceDetectors) {
                if (propertySourceDetector.support(suffix)) {
                    propertySourceDetector.load(environment, name, resource);
                    return;
                }
            }
        }
    }
}

最后添加一个配置类作为入口：

public class PropertySourceDetectorConfiguration implements ImportBeanDefinitionRegistrar {

    private static final String PATH_PREFIX = "profiles";

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
        DefaultListableBeanFactory beanFactory = (DefaultListableBeanFactory) registry;
        ConfigurableEnvironment environment = beanFactory.getBean(ConfigurableEnvironment.class);
        List<AbstractPropertySourceDetector> propertySourceDetectors = new ArrayList<>();
        configurePropertySourceDetectors(propertySourceDetectors, beanFactory);
        PropertySourceDetectorComposite propertySourceDetectorComposite = new PropertySourceDetectorComposite();
        propertySourceDetectorComposite.addPropertySourceDetectors(propertySourceDetectors);
        String[] activeProfiles = environment.getActiveProfiles();
        ResourcePatternResolver resourcePatternResolver = new PathMatchingResourcePatternResolver();
        try {
            for (String profile : activeProfiles) {
                String location = PATH_PREFIX + File.separator + profile + File.separator + "*";
                Resource[] resources = resourcePatternResolver.getResources(location);
                for (Resource resource : resources) {
                    propertySourceDetectorComposite.load(environment, resource.getFilename(), resource);
                }
            }
        } catch (IOException e) {
            throw new IllegalStateException(e);
        }
    }

    private void configurePropertySourceDetectors(List<AbstractPropertySourceDetector> propertySourceDetectors,
                                                  DefaultListableBeanFactory beanFactory) {
        Map<String, AbstractPropertySourceDetector> beansOfType = beanFactory.getBeansOfType(AbstractPropertySourceDetector.class);
        for (Map.Entry<String, AbstractPropertySourceDetector> entry : beansOfType.entrySet()) {
            propertySourceDetectors.add(entry.getValue());
        }
        propertySourceDetectors.add(new JsonPropertySourceDetector());
        propertySourceDetectors.add(new YamlPropertySourceDetector());
        propertySourceDetectors.add(new PropertiesPropertySourceDetector());
    }
}

准备就绪，在/resources/profiles/dev下面添加两个文件app.json和conf：

//app.json
{
  "app": {
    "name": "throwable",
    "age": 25
  }
}
//conf
name=doge

项目的application.yaml添加属性spring.profiles.active: dev，最后添加一个CommandLineRunner的实现用来观察数据：

@Slf4j
@Component
public class CustomCommandLineRunner implements CommandLineRunner {

    @Value("${app.name}")
    String name;
    @Value("${app.age}")
    Integer age;
    @Autowired
    ConfigurableEnvironment configurableEnvironment;

    @Override
    public void run(String... args) throws Exception {
        log.info("name = {},age = {}", name, age);
    }
}

自动装配的属性值和Environment实例中的属性和预期一样，改造是成功的。

小结

Spring中的环境属性管理的源码个人认为是最清晰和简单的：从文件中读取数据转化为key-value结构，key-value结构存放在一个PropertySource实例中，然后得到的多个PropertySource实例存放在一个CopyOnWriteArrayList中，属性访问的时候总是遍历CopyOnWriteArrayList中的PropertySource进行匹配。可能相对复杂的就是占位符的解析和参数类型的转换，后者牵连到Converter体系，这些不在本文的讨论范围内。最后附上一张Environment存储容器的示例图：

参考资料：

• spring-boot-starter-web:2.0.3.RELEASE源码。