What does the following piece of code actually do?

There is test method which accepts HttpServletRequest and HttpServletResponse. It returns ModelAndView. Before returing the model and view object the response is being redirected to /xyz . If I omit response.sendRedirect(request.getContextPath() + "/xyz"); line of code then the URL in my browser is localhost:8080/project/abc however adding that line of code makes the URL in the browser localhost:8080/project/xyz.

 public ModelAndView test(HttpServletRequest request, HttpServletResponse response) {
        LOGGER.info("Request for dashboard ");
        ModelAndView modelAndView = new ModelAndView();
        response.sendRedirect(request.getContextPath() + "/xyz");
        modelAndView.setViewName("index");
        return modelAndView;
    }

Now if I donot set the view name in the above code then it results in an error.

public ModelAndView test(HttpServletRequest request, HttpServletResponse response) {
            LOGGER.info("Request for dashboard ");
            ModelAndView modelAndView = new ModelAndView();
            response.sendRedirect(request.getContextPath() + "/xyz");
            return modelAndView;
        }

What exactly is happining under covers?