Difference between redirect and view rendering in Spring MVC

Question

In learning about Spring MVC knowledge, there are some things about Spring return types that confuse me.

In this documentation: Mapping Requests With @RequestMapping they return appointments/new and redirect:/appointments .

Code

@RequestMapping(method = RequestMethod.POST)
public String add(@Valid AppointmentForm appointment, BindingResult result) {
    if (result.hasErrors()) {
        return "appointments/new";
    }
    appointmentBook.addAppointment(appointment);
    return "redirect:/appointments";
}

What's is the main difference between these two return types? As I understand it, the first type returns as a forward action, but if I'm right, why do they also publish forward:/ as a return type ?

Answer 1

First one returns the view while the later redirects to another controller request mapped action. Lets have alook from the code itself.

@RequestMapping(method = RequestMethod.POST)
public String add(@Valid AppointmentForm appointment, BindingResult result) {
    if (result.hasErrors()) {
        return "appointments/new";
    }

Here when the result have errors, it renders the view appointments/new so that the user can enter the correct details and add the apppointment again. URL will not change in the browser

    appointmentBook.addAppointment(appointment);
    return "redirect:/appointments";
}

But here, when the results has no error, this controller action redirect the website to the URL /appointments . Check the web browser URL which is changed to the redirected URL

Regarding forward: vs redirect:

Quoted from this Satckoverflow answer Why do we use redirect in Spring MVC

Using the redirect prefix in your controller will generate a HTTP response with the 302 status code and the location header pointing to the redirection URL. The browser will then redirect to that URL (model exposed in the first request will be lost, and the browser URL will be the second one ).

Using the forward prefix, the forward will be done internally by the servlet, so there's no need of a second request (URL will remain the same) . The forward prefix should only be used in requests that can be safely repeated by the browser. That's not the case when you send a form which changes the database state (reloading the browser will lead to duplicate submissions). In these cases you should use redirect and apply the POST-redirect-GET pattern.

Answer 2

Doing a return of the view name, such as:

return new ModelAndView(<viewpath>/<viewname>);

Doesn't do a forward or a redirect, instead it actually grabs that file server side and processes it as the browser output.

When you return a "redirect:/somePath" it's actually sending a redirect (not a forward) to the browser. A redirect causes a page refresh and happens in the browser and a forward happens on the server side and doesn't change your URL.

Answer 3

Se this link. It explains what the difference is between redirect and forward