private void handleMessage(ChannelAgent<T> agent, T message) {
        K key = this.keyMapper.apply(message);
        V value = this.valueMapper.apply(message);
        this.messageStore.put(key, value);
    }
Creates a new mapped channel receiver.

@param channel the channel
@param keyMapper the function used to map keys
@param map the map instance used to back the instance
@param <T> the message type
@param <K> the key type
@return a new mapped channel receiver
helper/src/main/java/me/lucko/helper/messaging/util/MappedChannelReceiver.java