@Override
    public String toString() {
        String strVal = this.strVal;
        if (strVal == null) {
            this.strVal = strVal = toString(getClass(), localAddress(), protocols(), portGroup());
        }

        return strVal;
    }
Returns the port group this {@link ServerPort} belongs to, or {@code 0} if this {@link ServerPort}
doesn't belong to any port group.
core/src/main/java/com/linecorp/armeria/server/ServerPort.java