Redirecting to External URLs from Spring MVC Controller Actions

In Spring MVC, redirecting to URLs within the project is straightforward using the redirect: prefix. However, redirecting to external URLs can be tricky, especially if the URL does not specify a valid protocol.

Consider the following code, which redirects to a URL within the project:

@RequestMapping(method = RequestMethod.POST)
public String processForm(HttpServletRequest request, LoginForm loginForm, 
                          BindingResult result, ModelMap model) 
{
    String redirectUrl = "yahoo.com";
    return "redirect:"   redirectUrl;
}

This code will not redirect to the intended external URL but instead redirect to a view with the given name. To redirect to external URLs, one must include the protocol in the URL, as seen below:

@RequestMapping(method = RequestMethod.POST)
public String processForm(HttpServletRequest request, LoginForm loginForm, 
                              BindingResult result, ModelMap model) 
{
    String redirectUrl = "http://www.yahoo.com";
    return "redirect:"   redirectUrl;
}

However, this method requires the presence of a valid protocol. To handle URLs without valid protocols, two approaches are available:

Approach 1:

@RequestMapping(value = "/redirect", method = RequestMethod.GET)
public void method(HttpServletResponse httpServletResponse) {
    httpServletResponse.setHeader("Location", projectUrl);
    httpServletResponse.setStatus(302);
}

In this approach, a HttpServletResponse object is used to set the location header and status code, forcing the redirect.

Approach 2:

@RequestMapping(value = "/redirect", method = RequestMethod.GET)
public ModelAndView method() {
    return new ModelAndView("redirect:"   projectUrl);
}

This approach employs a ModelAndView to redirect to the given URL.