public class BeansDtdResolver extends Object implements EntityResolver
EntityResolver implementation for the Spring beans DTD,
to load the DTD from the Spring class path (or JAR file).
Fetches "spring-beans.dtd" from the class path resource "/org/springframework/beans/factory/xml/spring-beans.dtd", no matter whether specified as some local URL that includes "spring-beans" in the DTD name or as "https://www.springframework.org/dtd/spring-beans-2.0.dtd".
ResourceEntityResolver@Nullable public InputSource resolveEntity(@Nullable String publicId, @Nullable String systemId) throws IOException
resolveEntity 在接口中 EntityResolverIOException