Spring中的@PropertySource注解源码详细解析
作者：mumubili
这篇文章主要介绍了Spring中的@PropertySource注解源码详细解析,@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,需要的朋友可以参考下
前言
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<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));
}
}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 <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；
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