public static FieldsHelper forClass(final Class<?> targetClass) {
        return HELPER_MAP.computeIfAbsent(targetClass, FieldsHelper::new);
    }
The mappings from the field name to its {@code setter}.
oap-server/server-library/library-util/src/main/java/org/apache/skywalking/oap/server/library/util/FieldsHelper.java