[GSS](7.3.z) Xalan XML to stream transformation produces wrong encoding

An XML transformation from XML (DOMSource) to String (StreamSource) using encoding "ISO-8859-1" produces Unicode decimal encoding instead of ISO-8859-1 within EAP running with JDK 11.

Encoding "ISO-8859-1" is configured by:

lTransformer.setOutputProperty(OutputKeys.ENCODING, "ISO-8859-1");

By means of service loader configurtion of xalan-2.7.1.redhat-12.jar org.apache.xalan.processor.TransformerFactoryImpl is used as implementation of javax.xml.transform.TransformerFactory.

Please find attached XalanTransformation.zip which can be used to reproduce the issue and also to show different behaviour between using JDK 8 and JDK 11.

c:\progra~1\java\jdk-11.0.9.0.3\bin\java -cp .;serializer-2.7.1.redhat-12.jar;xalan-2.7.1.redhat-12.jar XalanTransformation
<?xml version="1.0" encoding="ISO-8859-1"?><Name>H&#252;bner</Name

c:\progra~1\java\jdk1.8.0_271\bin\java -cp .;serializer-2.7.1.redhat-12.jar;xalan-2.7.1.redhat-12.jar XalanTransformation
<?xml version="1.0" encoding="ISO-8859-1"?><Name>Hübner</Name>
 

The issue seems to be caused by the mechanism xalan uses to register the encodings from serializer-2.7.1.redhat-12.jar\org\apache\xml\serializer\Encodings.properties. The file contains:

ISO8859-1 ISO-8859-1 0x00FF
ISO8859_1 ISO-8859-1 0x00FF
8859-1 ISO-8859-1 0x00FF
8859_1 ISO-8859-1 0x00FF 

and registers the Java names (left column) and the Mime names (middle column).

The encoding used by the transformation is looked up b means of the Mime name "ISO-8859-1". Which Java encoding is actually used for the string encoding apparently depends on the order of encoding registration to org.apache.xml.serializer.Encodings._encodingTableKeyMime. For JDK 11 8859-1
is registered last and therefore used for transformation. It produces an UnsupportedEncodingException so that xalan writes unicode decimal as fallback plan.

When JDK 8 is used ISO8859_1 is registered last and therefore used for transformation. This encoding successfully encodes ISO-8859-1.