version 2.x is support Expression Language，How to use in 3.x

[fudewei1]

version 2x for example ;

Transformer transformer = TransformerFactory.createTransformer(is, os);
 ...
 JexlExpressionEvaluator evaluator = (JexlExpressionEvaluator) transformer.getTransformationConfig().getExpressionEvaluator();
 Map<String, Object> functionMap = new HashMap<>();
 functionMap.put("demo", new JexlCustomFunctionDemo());
 evaluator.getJexlEngine().setFunctions(functionMap);

How to use in 3.x?