code: public static void setMdcFields(String spec, GelfMessageAssembler gelfMessageAssembler) {
          if (null != spec) {
              String[] fields = spec.split(MULTI_VALUE_DELIMITTER);
  
              for (String field : fields) {
                  gelfMessageAssembler.addField(new MdcMessageField(field.trim(), field.trim()));
              }
          }
      }
docs: Set the MDC fields.
  
  @param spec field, field2, field3
  @param gelfMessageAssembler the Gelf message assembler to apply the configuration