@Override
    public Object parse(SourceData sourceData, int rowIndex, Context context) {
        Object stringObject = stringParser.parse(sourceData, rowIndex, context);
        if (stringObject == null) {
            return false;
        }
        String string = OperatorTools.parseString(stringObject);
        if (string.isEmpty()) {
            return false;
        }
        for (char chr : string.toCharArray()) {
            if ((chr >= 'a' && chr <= 'z') || (chr >= 'A' && chr <= 'Z')) {
                continue;
            }
            return false;
        }
        return true;
    }
IsAlphaFunction  ->  is_alpha(string)
description:
- Return true if all characters in string are letter
- Return false otherwise (Including cases where string is null and '').
inlong-sdk/transform-sdk/src/main/java/org/apache/inlong/sdk/transform/process/function/string/IsAlphaFunction.java