This is my own coding and it will have some bugs or error but until now its still running well on my apps. Firstly, create a class for handling device input and name it as inputhandler.

public class InputHandler implements InputProcessor {
  private int downX;
  private int downY;
  @Override
  public boolean touchDown(int screenX, int screenY, int pointer, int button) {
    downX = screenX;
    downY = screenY;
    return true;
  }
  @Override
  public boolean touchUp(int screenX, int screenY, int pointer, int button) {
  gameHandler.onSwipe(screenX, screenY, downX, downY);
  return true;
  }
}

This is just a part of my coding, you should add all the required unimplemented methods and don’t forget to add the necessary Import function or just press Ctrl + o
In your game handler, for example in gameHandler class put this code

public class gameHandler {
   public void onSwipe(int X, int Y, int downX, int downY) {
   String direction = "";
   if(Math.abs(X-downX) > Math.abs(Y-downY)){
      if(X > downX){
        direction = "right";
      } else if(X < downX){
        direction = "left";
      }
   }else{
     if(Y > downY){
        direction = "down";
     } else if(Y < downY){
        direction = "up";
     }
   }
   }
}

downX and downY will be the initial position when finger touching the screen while X and Y is the current position when finger touch up the screen. By using this value we can defined the swipe direction.