package bot;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;


@Controller
@RequestMapping("/webhook")
public class BotController {

    @RequestMapping(method = RequestMethod.POST)
    public @ResponseBody WebhookResponse webhook(@RequestBody String obj){

        System.out.println(obj);


        return new WebhookResponse("https://www.google.com", "https://www.google.com");
    }
}

package bot;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;


@Controller
@RequestMapping("/webhook")
public class BotController {

    @RequestMapping(method = RequestMethod.POST)
    public @ResponseBody WebhookResponse webhook(@RequestBody String obj){

        System.out.println(obj);


        return new WebhookResponse("https://www.google.com"+"\n"+"https://facebook.com", "https://www.google.com");
    }
}

Update BotController.java