public float qualityFactor(float defaultValueIfNotSpecified) {
        // Find 'q' or 'Q'.
        final List<String> qValues = parameters().get(Q);
        if (qValues == null || qValues.isEmpty()) {
            // qvalue does not exist.
            return defaultValueIfNotSpecified;
        }

        try {
            // Parse the qvalue. Make sure it's within the range of [0, 1].
            return Math.max(Math.min(Float.parseFloat(qValues.get(0)), 1.0f), 0.0f);
        } catch (NumberFormatException e) {
            // The range with a malformed qvalue gets the lowest possible preference.
            return 0.0f;
        }
    }
Returns the quality factor of this {@link MediaType}. If it is not specified,
{@code defaultValueIfNotSpecified} will be returned.
core/src/main/java/com/linecorp/armeria/common/MediaType.java