When a controller method processes a request, Spring MVC provides multiple approaches to handle the repsonse.

Void Return Type

@RequestMapping("/processVoid")
public void handleVoidRequest() throws Exception {
    System.out.println("Void handler method executed");
}

When a controller method returns void, Spring MVC attempts to locate a view matching the method name. Without view resolver configuration, this may result in 404 errors.

Servlet API Forward and Redirect

@RequestMapping("servletDemo")
public void handleServletResponse(HttpServletRequest req, HttpServletResponse resp) throws Exception {
    // Request forwarding
    // req.getRequestDispatcher("/target.jsp").forward(req, resp);
    
    // Response redirect
    resp.sendRedirect(req.getContextPath() + "/redirect.jsp");
}

Using HttpServletResponse directly bypasses DispatcherServlet's standard response handling.

Forward Keyword Approach

@RequestMapping("forwardDemo")
public String handleForward() throws Exception {
    // Explicit forward
    // return "forward:/destination.jsp";
    
    // Implicit forward (forward keyword omitted)
    return "/targetPage.jsp";
}

The forward keyword can be omitted when performing request forwarding.

Redirect Keyword Approach

@RequestMapping("redirectDemo")
public String handleRedirect() throws Exception {
    return "redirect:/newLocation.jsp";
}

The redirect keyword is mandatory for response redirection.

View Interface Implementation

@RequestMapping("viewDemo")
public View handleViewResponse(HttpServletRequest request) {
    View resultView = null;
    
    // Internal resource view (forwarding)
    // resultView = new InternalResourceView("/internal.jsp");
    
    // Redirect view
    resultView = new RedirectView(request.getContextPath() + "/external.jsp");
    
    return resultView;
}

RedirectView handles URL redirection and supports data preservation through FlashMap.

ModelAndView Aprpoach

@RequestMapping("modelViewDemo")
public ModelAndView handleModelAndView(HttpServletRequest req) {
    ModelAndView modelView = new ModelAndView();
    
    // Forward using view name
    // modelView.setViewName("forward:/page.jsp");
    
    // Forward using View object
    // modelView.setView(new InternalResourceView("/resource.jsp"));
    
    // Redirect using view name
    // modelView.setViewName("redirect:/newPage.jsp");
    
    // Redirect using View object
    modelView.setView(new RedirectView(req.getContextPath() + "/external.jsp"));
    
    return modelView;
}

ModelAndView encapsulates both data model and view information for comprehensive response handling.

JSON Response with @ResponseBody

For AJAX requests, Spring MVC can directly return JSON data instead of view resolution.

Dependency Configuration

<dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.12.1</version>
</dependency>

Controller Implementation

@ResponseBody
@RequestMapping("ajaxHandler")
public Animal processAjaxRequest(User user) throws JsonProcessingException {
    System.out.println(user);
    Animal animal = new Animal("Max", "dog");
    return animal;
}

@ResponseBody instructs Spring MVC to treat the return value as direct response data rather than view information.

Client-Side Implementation

<script>
    $(function(){
        $("#ajaxButton").click(function(){
            $.get("ajaxHandler", {username:"john", age:"25"}, function(response){
                console.log(response.animalName);
                console.log(response.animalSpecies);
            });
        });
    });
</script>

@RestController Annotation

@RestController
public class RestApiController {
    @RequestMapping("restEndpoint")
    public Animal handleRestCall(User person) throws JsonProcessingException {
        System.out.println(person);
        Animal pet = new Animal("Buddy", "dog");
        return pet;
    }
}

@RestController combines @Controller and @ResponseBody functionality, automatically serializing return values to JSON. This annotation prevents JSP/HTML view resolution.