Spring源码：@PropertySource源码解析

目录

1. @PropertySource处理入口

2. @PropertySource注解解析

3. 构造ResourcePropertySource对象

4. PropertySource配置加载到environment当中

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通常，我们在开发java spring项目时，会包含多套环境（profile），并且分别提供了不同环境下的属性文件（.properties），在引用属性文件时，都会用到@PropertySource注解，标注在配置类@Configuration上面，下面主要分析一下@PropertySource注解的处理过程，也就是怎么把配置信息从.properies文件放到environment中的；

1. @PropertySource处理入口

@PropertySource使用时都会和@Configuration放在一起，对@PropertySource的处理也是放在@Configuration解析处理过程中的（对@Configuration的处理过程后面再单独进行分析），参见源码如下：

/**
	 * Apply processing and build a complete {@link ConfigurationClass} by reading the
	 * annotations, members and methods from the source class. This method can be called
	 * multiple times as relevant sources are discovered.
	 * @param configClass the configuration class being build
	 * @param sourceClass a source class
	 * @return the superclass, or {@code null} if none found or previously processed
	 */
	protected final SourceClass doProcessConfigurationClass(ConfigurationClass configClass, SourceClass sourceClass)
			throws IOException {

		// Recursively process any member (nested) classes first
		processMemberClasses(configClass, sourceClass);

		// Process any @PropertySource annotations
		for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
				sourceClass.getMetadata(), PropertySources.class,
				org.springframework.context.annotation.PropertySource.class)) {
			if (this.environment instanceof ConfigurableEnvironment) {
				processPropertySource(propertySource);
			}
			else {
				logger.warn("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
						"]. Reason: Environment must implement ConfigurableEnvironment");
			}
		}

    //......其余部分省略
}

上面for循环处理的过程，实质上主要包含了两步：

• 解析@PropertySource注解，包括单独声明的@PropertySource注解，以及在容器注解@PropertySources value属性中指定的注解；
• 将解析的@PropertySource注解放到environment中；

下面分别对这两个过程进行分析；

2. @PropertySource注解解析

解析过程主要封装到了AnnotationConfigUtils.attributesForRepeatable(sourceClass.getMetadata(), PropertySources.class, org.springframework.context.annotation.PropertySource.class)当中，根据进去源码如下：

static Set attributesForRepeatable(
			AnnotationMetadata metadata, String containerClassName, String annotationClassName) {

		Set result = new LinkedHashSet();

		// Direct annotation present?
		addAttributesIfNotNull(result, metadata.getAnnotationAttributes(annotationClassName, false));

		// Container annotation present?
		Map container = metadata.getAnnotationAttributes(containerClassName, false);
		if (container != null && container.containsKey("value")) {
			for (Map containedAttributes : (Map[]) container.get("value")) {
				addAttributesIfNotNull(result, containedAttributes);
			}
		}

		// Return merged result
		return Collections.unmodifiableSet(result);
	}

private static void addAttributesIfNotNull(Set result, Map attributes) {
		if (attributes != null) {
			result.add(AnnotationAttributes.fromMap(attributes));
		}
	}

这里，首先获取配置类上@PropertySource注解，解析成AnnotationAttributes map对象，放到result中；

然后解析容器注解@PropertySources value属性值，并将解析的@PropertySource列表放到result中；

这样@PropertySource注解和@PropertySources容器注解解析完毕；

3. 构造ResourcePropertySource对象

这里主要分析一下processPropertySource(propertySource)的过程，源码如下：

/**
	 * Process the given @PropertySource annotation metadata.
	 * @param propertySource metadata for the @PropertySource annotation found
	 * @throws IOException if loading a property source failed
	 */
	private void processPropertySource(AnnotationAttributes propertySource) throws IOException {
		String name = propertySource.getString("name");
		if (!StringUtils.hasLength(name)) {
			name = null;
		}
		String encoding = propertySource.getString("encoding");
		if (!StringUtils.hasLength(encoding)) {
			encoding = null;
		}
		String[] locations = propertySource.getStringArray("value");
		Assert.isTrue(locations.length > 0, "At least one @PropertySource(value) location is required");
		boolean ignoreResourceNotFound = propertySource.getBoolean("ignoreResourceNotFound");

		Class factoryClass = propertySource.getClass("factory");
		PropertySourceFactory factory = (factoryClass == PropertySourceFactory.class ?
				DEFAULT_PROPERTY_SOURCE_FACTORY : BeanUtils.instantiateClass(factoryClass));

		for (String location : locations) {
			try {
				String resolvedLocation = this.environment.resolveRequiredPlaceholders(location);
				Resource resource = this.resourceLoader.getResource(resolvedLocation);
				addPropertySource(factory.createPropertySource(name, new EncodedResource(resource, encoding)));
			}
			catch (IllegalArgumentException ex) {
				// Placeholders not resolvable
				if (ignoreResourceNotFound) {
					if (logger.isInfoEnabled()) {
						logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());
					}
				}
				else {
					throw ex;
				}
			}
			catch (IOException ex) {
				// Resource not found when trying to open it
				if (ignoreResourceNotFound &&
						(ex instanceof FileNotFoundException || ex instanceof UnknownHostException)) {
					if (logger.isInfoEnabled()) {
						logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());
					}
				}
				else {
					throw ex;
				}
			}
		}
	}

其中@PropertySource的主要属性value（这里放到了locations中）保存了属性文件的存放位置，对每一个location的解析主要分为如下3步：

• 解析location中包含的占位符
• 加载Resource对象
• 构造ResourcePropertySource对象
• PropertySource加载到environment当中

其中第三步构造ResourcePropertySource主要用到了PropertySourceFactory，这里默认实现是DefaultPropertySourceFactory，内部实现源码如下：

/**
 * The default implementation for {@link PropertySourceFactory},
 * wrapping every resource in a {@link ResourcePropertySource}.
 *
 * @author Juergen Hoeller
 * @since 4.3
 * @see PropertySourceFactory
 * @see ResourcePropertySource
 */
public class DefaultPropertySourceFactory implements PropertySourceFactory {

	@Override
	public PropertySource createPropertySource(String name, EncodedResource resource) throws IOException {
		return (name != null ? new ResourcePropertySource(name, resource) : new ResourcePropertySource(resource));
	}

}

上面主要通过resource构造了ResourcePropertySource对象，其构造函数如下：

/**
	 * Create a PropertySource based on Properties loaded from the given resource.
	 * The name of the PropertySource will be generated based on the
	 * {@link Resource#getDescription() description} of the given resource.
	 */
	public ResourcePropertySource(EncodedResource resource) throws IOException {
		super(getNameForResource(resource.getResource()), PropertiesLoaderUtils.loadProperties(resource));
		this.resourceName = null;
	}

如上，可见先是由resource构造了Peoperties对象，然后构造了PropertiesPropertySource父类.....

如下是ResourcePropertySource的继承结构，最终加载的属性值放入到了PropertySource的成员变量source中；

4. PropertySource配置加载到environment当中

构造完ResourcePropertySource对象之后，下面将该对象放入到environment中，源码如下：

private void addPropertySource(PropertySource propertySource) {
		String name = propertySource.getName();
		MutablePropertySources propertySources = ((ConfigurableEnvironment) this.environment).getPropertySources();
		if (propertySources.contains(name) && this.propertySourceNames.contains(name)) {
			// We've already added a version, we need to extend it
			PropertySource existing = propertySources.get(name);
			PropertySource newSource = (propertySource instanceof ResourcePropertySource ?
					((ResourcePropertySource) propertySource).withResourceName() : propertySource);
			if (existing instanceof CompositePropertySource) {
				((CompositePropertySource) existing).addFirstPropertySource(newSource);
			}
			else {
				if (existing instanceof ResourcePropertySource) {
					existing = ((ResourcePropertySource) existing).withResourceName();
				}
				CompositePropertySource composite = new CompositePropertySource(name);
				composite.addPropertySource(newSource);
				composite.addPropertySource(existing);
				propertySources.replace(name, composite);
			}
		}
		else {
			if (this.propertySourceNames.isEmpty()) {
				propertySources.addLast(propertySource);
			}
			else {
				String firstProcessed = this.propertySourceNames.get(this.propertySourceNames.size() - 1);
				propertySources.addBefore(firstProcessed, propertySource);
			}
		}
		this.propertySourceNames.add(name);
	}

注意，这里对于@PropertySource注解获取的配置属性放入到了environment的后面，实际在application.properties后面，也即application.properties的优先级高于@PropertySource引入的配置，后面单独对这块进行分析；