目錄
4. PropertySource配置加載到environment當中
通常，我們在開發java spring項目時，會包含多套環境（profile），並且分別提供了不同環境下的屬性文件（.properties），在引用屬性文件時，都會用到@PropertySource註解，標註在配置類@Configuration上面，下面主要分析一下@PropertySource註解的處理過程，也就是怎麼把配置信息從.properies文件放到environment中的；
1. @PropertySource處理入口
@PropertySource使用時都會和@Configuration放在一起，對@PropertySource的處理也是放在@Configuration解析處理過程中的（對@Configuration的處理過程後面再單獨進行分析），參見源碼如下：
/**
* 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");
}
}
//......其餘部分省略
}
上面for循環處理的過程，實質上主要包含了兩步：
- 解析@PropertySource註解，包括單獨聲明的@PropertySource註解，以及在容器註解@PropertySources value屬性中指定的註解；
- 將解析的@PropertySource註解放到environment中；
下面分別對這兩個過程進行分析；
2. @PropertySource註解解析
解析過程主要封裝到了AnnotationConfigUtils.attributesForRepeatable(sourceClass.getMetadata(), PropertySources.class, org.springframework.context.annotation.PropertySource.class)當中，根據進去源碼如下：
static Set<AnnotationAttributes> attributesForRepeatable(
AnnotationMetadata metadata, String containerClassName, String annotationClassName) {
Set<AnnotationAttributes> result = new LinkedHashSet<AnnotationAttributes>();
// Direct annotation present?
addAttributesIfNotNull(result, metadata.getAnnotationAttributes(annotationClassName, false));
// Container annotation present?
Map<String, Object> container = metadata.getAnnotationAttributes(containerClassName, false);
if (container != null && container.containsKey("value")) {
for (Map<String, Object> containedAttributes : (Map<String, Object>[]) container.get("value")) {
addAttributesIfNotNull(result, containedAttributes);
}
}
// Return merged result
return Collections.unmodifiableSet(result);
}
private static void addAttributesIfNotNull(Set<AnnotationAttributes> result, Map<String, Object> attributes) {
if (attributes != null) {
result.add(AnnotationAttributes.fromMap(attributes));
}
}
這裏，首先獲取配置類上@PropertySource註解，解析成AnnotationAttributes map對象，放到result中；
然後解析容器註解@PropertySources value屬性值，並將解析的@PropertySource列表放到result中；
這樣@PropertySource註解和@PropertySources容器註解解析完畢；
3. 構造ResourcePropertySource對象
這裏主要分析一下processPropertySource(propertySource)的過程，源碼如下：
/**
* Process the given <code>@PropertySource</code> annotation metadata.
* @param propertySource metadata for the <code>@PropertySource</code> 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<? extends PropertySourceFactory> 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的主要屬性value（這裏放到了locations中）保存了屬性文件的存放位置，對每一個location的解析主要分爲如下3步：
- 解析location中包含的佔位符
- 加載Resource對象
- 構造ResourcePropertySource對象
- PropertySource加載到environment當中
其中第三步構造ResourcePropertySource主要用到了PropertySourceFactory，這裏默認實現是DefaultPropertySourceFactory，內部實現源碼如下：
/**
* 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));
}
}
上面主要通過resource構造了ResourcePropertySource對象，其構造函數如下：
/**
* 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，可見先是由resource構造了Peoperties對象，然後構造了PropertiesPropertySource父類.....
如下是ResourcePropertySource的繼承結構，最終加載的屬性值放入到了PropertySource的成員變量source中；
4. PropertySource配置加載到environment當中
構造完ResourcePropertySource對象之後，下面將該對象放入到environment中，源碼如下：
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，這裏對於@PropertySource註解獲取的配置屬性放入到了environment的後面，實際在application.properties後面，也即application.properties的優先級高於@PropertySource引入的配置，後面單獨對這塊進行分析；