springboot中Properties注解的实现

　　关于@PropertySources注解的理解：http://www.imooc.com/article/252889?block_id=tuijian_wz

public interface PropertySources extends Iterable<PropertySource<?>> {
 
    /**
     * Return a sequential {@link Stream} containing the property sources.
     * @since 5.1
     */
    default Stream<PropertySource<?>> stream() {
        return StreamSupport.stream(spliterator(), false);
    }
    /**
     * Return whether a property source with the given name is contained.
     * @param name the {@linkplain PropertySource#getName() name of the property source} to find
     */
    boolean contains(String name);
 
    /**
     * Return the property source with the given name, {@code null} if not found.
     * @param name the {@linkplain PropertySource#getName() name of the property source} to find
     */
    @Nullable
    PropertySource<?> get(String name);
这就是PropertySources的接口，那么它的实现类在哪里？是MutablePropertySources,
}

　　PropertySources是由工厂类生成的，看看DefaultPropertySourceFactory

public class DefaultPropertySourceFactory implements PropertySourceFactory {

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

}

然后又调用ResourcePropertySource类，在该类下，实现了对配置文件的加载loadProperties(resource).

public class ResourcePropertySource extends PropertiesPropertySource {
 
    /** The original resource name, if different from the given name. */
    @Nullable
    private final String resourceName;
 
 
    /**
     * Create a PropertySource having the given name based on Properties
     * loaded from the given encoded resource.
     */
    public ResourcePropertySource(String name, EncodedResource resource) throws IOException {
        super(name, PropertiesLoaderUtils.loadProperties(resource));
        this.resourceName = getNameForResource(resource.getResource());
    }