This interface is used to resolve resources during an XML parse. If an application wishes to
perform custom entity resolution it must register an instance of this interface with
the XMLInputFactory using the setXMLResolver method.
Retrieves a resource. This resource can be of the following three return types:
(1) java.io.InputStream (2) javax.xml.stream.XMLStreamReader (3) java.xml.stream.XMLEventReader.
If this method returns null the processor will attempt to resolve the entity using its
publicID - The public identifier of the external entity being referenced, or null if none was supplied.
systemID - The system identifier of the external entity being referenced.
baseURI - Absolute base URI associated with systemId.
namespace - The namespace of the entity to resolve.