Spring中的@PropertySource注解源码详解
作者：drunk in spring
这篇文章主要介绍了Spring中的@PropertySource注解源码详解,@PropertySource注解用于指定资源文件读取的位置,它不仅能读取properties文件,也能读取xml文件,并且通过yaml解析器,配合自定义PropertySourceFactory实现解析yaml文件,需要的朋友可以参考下
@PropertySource注解使用
@PropertySource注解用于指定资源文件读取的位置，它不仅能读取properties文件，也能读取xml文件，并且通过yaml解析器，配合自定义PropertySourceFactory实现解析yaml文件
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Repeatable(PropertySources.class)
public @interface PropertySource {
//资源名称，为空则根据资源的描述符生成
String name() default "";
/**
*资源路径
*classpath:application.properties
*file:/
*/
String[] value();
//是否忽略资源不存在的情况，如果不忽略，当资源不存在时报错
boolean ignoreResourceNotFound() default false;
//指定资源文件的编码格式
String encoding() default "";
//资源工厂
Class<? extends PropertySourceFactory> factory() default PropertySourceFactory.class;
}源码解析
在bean实例化之前有一个ConfigurationClassPostProcessor类，会操作BeanDefinition并且加入到BeanDefinitionRegistry中，它的优先级在所有的BeanDefinitionRegistryPostProcessor里面是最低的。
优先级：最低
public int getOrder() {
return Ordered.LOWEST_PRECEDENCE; // within PriorityOrdered
}
会在这个类中进行相关注解的解析操作，在进行@PropertySource注解解析的时候要借助ConfigurationClassParser的parse方法
在进行@PropertySource注解解析之前，需要拿到两个对象ConfigurationClass和SourceClass
bean的元数据信息（bd.getMetadata），和beanName，封装成ConfigurationClass对象
new ConfigurationClass(metadata, beanName)
SourceClass这个对象理解为跟类或者接口对应，然后把metadata对象包装进去
SourceClass sourceClass = asSourceClass(configClass, filter);
接下来正式进入解析流程
for (AnnotationAttributes propertySource : AnnotationConfigUtils.attributesForRepeatable(
sourceClass.getMetadata(), PropertySources.class,
org.springframework.context.annotation.PropertySource.class)) {
if (this.environment instanceof ConfigurableEnvironment) {
//核心逻辑
processPropertySource(propertySource);
}
else {
logger.info("Ignoring @PropertySource annotation on [" + sourceClass.getMetadata().getClassName() +
"]. Reason: Environment must implement ConfigurableEnvironment");
}
}
拿到类上面的所有PropertySource注解的值AnnotationAttributes，放到processPropertySource方法中进行解析
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;
}
//获取配置文件路径
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 {
//替换占位符
String resolvedLocation = this.environment.resolveRequiredPlaceholders(location);
//流的方式加载配置文件并封装成Resource对象
Resource resource = this.resourceLoader.getResource(resolvedLocation);
//加载Resource中的配置属性封装成Properties对象中，并创建PropertySource对象加入到Environment对象中
addPropertySource(factory.createPropertySource(name, new EncodedResource(resource, encoding)));
}
catch (IllegalArgumentException | FileNotFoundException | UnknownHostException ex) {
// Placeholders not resolvable or resource not found when trying to open it
if (ignoreResourceNotFound) {
if (logger.isInfoEnabled()) {
logger.info("Properties location [" + location + "] not resolvable: " + ex.getMessage());
}
}
else {
throw ex;
}
}
}
}
这里看一下createPropertySource方法，就是将配置文件中的内容封装成ResourcePropertySource对象，作为属性源
public PropertySource<?> createPropertySource(@Nullable String name, EncodedResource resource) throws IOException {
return (name != null ? new ResourcePropertySource(name, resource) : new ResourcePropertySource(resource));
}
属性源拿到之后，要统一交给Environment管理，调用addPropertySource方法
private void addPropertySource(PropertySource<?> propertySource) {
String name = propertySource.getName();
//获取Environment对象中的MutablePropertySources
MutablePropertySources propertySources = ((ConfigurableEnvironment) this.environment).getPropertySources();
//如果已经存在了该配置文件的PropertySource则合并久的
if (this.propertySourceNames.contains(name)) {
// We've already added a version, we need to extend it
PropertySource<?> existing = propertySources.get(name);
if (existing != null) {
PropertySource<?> newSource = (propertySource instanceof ResourcePropertySource ?
((ResourcePropertySource) propertySource).withResourceName() : propertySource);
//合并二次后的类型
if (existing instanceof CompositePropertySource) {
((CompositePropertySource) existing).addFirstPropertySource(newSource);
}
else {
if (existing instanceof ResourcePropertySource) {
existing = ((ResourcePropertySource) existing).withResourceName();
}
//其实就是CompositePropertySource里面有一个Set，Set里面装了新和旧的PropertySource对象
CompositePropertySource composite = new CompositePropertySource(name);
composite.addPropertySource(newSource);
composite.addPropertySource(existing);
propertySources.replace(name, composite);
}
return;
}
}
if (this.propertySourceNames.isEmpty()) {
propertySources.addLast(propertySource);
}
else {
//用于计算插入的位置index
String firstProcessed = this.propertySourceNames.get(this.propertySourceNames.size() - 1);
//吧propertySource对象存入MutablePropertySources的list中
propertySources.addBefore(firstProcessed, propertySource);
}
this.propertySourceNames.add(name);
}
拿到Environment中的MutablePropertySources，用来放置拿到的属性源。 如果有相同的属性源，则升级成CompositePropertySource，把新旧相同的属性源进行合并，再放到MutablePropertySources中
看看CompositePropertySource类的内部 有Set<PropertySource<?>> propertySources = new LinkedHashSet<>();用来放置属性源 也重写了getProperty方法
public Object getProperty(String name) {
for (PropertySource<?> propertySource : this.propertySources) {
Object candidate = propertySource.getProperty(name);
if (candidate != null) {
return candidate;
}
}
return null;
}
@PropertySource注解中配置的属性源都交给Environment管理
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