The bots running process is not normally exposed to the Web, so you wouldn’t build this into the bot itself but create a web visible service to capture the Webhook responses.
I’d do the same with PubSub myself, separate service.
Then both services receive the data and broadcast it internally to the bot if the bot needs that information.
You may want to grab a Twitch chat specific java library instead of PircBot to save you some time.
For the most part if you switch to long polling the API then you just need code that makes you make HTTP Get requests to the API and JSON stuff to parse the responses. I don’t write Java so I don’t have an existing codes with detailed comments