public Map<String, String> eval(String userAgentString) {
        return userAgentAnalyzer.parse(userAgentString).toMap(extractedFields);
    }
Create a UserAgentAnalyzer that extracts only the specified fields
@param cacheSize The desired size of the cache.
@param desiredFields The list of desired field names.
udfs/flink-table/src/main/java/nl/basjes/parse/useragent/flink/table/AnalyzeUseragentFunction.java