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

public interface PropertySources extends Iterable
     
      > {	/**	 * Return a sequential {@link Stream} containing the property sources.	 * @since 5.1	 */	default Stream
      
       > 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());	}

　　剩下的就是java的文件的加载过程，细节就不再讨论了