Master Spring MVC Controllers: From @Controller Basics to Advanced Techniques

1. Using @Controller construction

The simplest way to create a controller that can handle one or more requests is to annotate a class with @Controller. Example:

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

@Controller
public class HomeController {
    @RequestMapping("/")
    public String visitHome() {
        return "home";
    }
}

The visitHome() method redirects to the view named home. Note that @Controller works only when annotation‑driven configuration is enabled ( <annotation-driven />) and the component‑scan base package is set.

2. Implementing the Controller interface

Another classic approach is to let a class implement the Controller interface and override handleRequest(). The request URL pattern is defined in the Spring XML configuration:

<bean name="/main" class="net.codejava.spring.MainController" />

This method can handle only a single URL.

3. Extending AbstractController

Extending AbstractController simplifies handling supported HTTP methods, sessions, and caching. Example:

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.AbstractController;

public class BigController extends AbstractController {
    @Override
    protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response) throws Exception {
        System.out.println("You're big!");
        return new ModelAndView("big");
    }
}

Bean configuration can specify supported methods, e.g., POST.

4. Specifying URL mapping for handler methods

Use @RequestMapping to map URLs to controller methods or classes, e.g.:

@RequestMapping("/login")
public String viewLogin() { return "LoginForm"; }

Multiple URLs can be mapped with an array syntax.

5. Specifying HTTP request methods

Set the method attribute of @RequestMapping to restrict handling to GET, POST, etc. Example:

@Controller
public class LoginController {
    @RequestMapping(value="/login", method=RequestMethod.GET)
    public String viewLogin() { return "LoginForm"; }

    @RequestMapping(value="/login", method=RequestMethod.POST)
    public String doLogin() { return "Home"; }
}

6. Mapping request parameters to handler methods

Use @RequestParam to bind request parameters to method arguments, with optional required and defaultValue attributes. Example:

@RequestMapping(value="/login", method=RequestMethod.POST)
public String doLogin(@RequestParam String username, @RequestParam String password) { ... }

Parameters can also be collected into a Map<String,String>.

7. Returning model and view

Handler methods can return a view name as a String or a ModelAndView object. Example returning a ModelAndView with data:

@RequestMapping("/listUsers")
public ModelAndView listUsers() {
    List<User> listUser = new ArrayList<>(); // fetch from DAO
    ModelAndView mv = new ModelAndView("UserList");
    mv.addObject("listUser", listUser);
    return mv;
}

The same can be achieved by declaring ModelAndView as a method parameter.

8. Adding objects to the model

Use addObject() on ModelAndView or put entries into a Map<String,Object> to pass data to the view.

modelView.addObject("siteName", "CodeJava.net");
model.put("pageviews", 320000);

9. Redirecting from handler methods

Return a view name prefixed with redirect:/ to perform a redirect, e.g.:

if (!isLogin) {
    return new ModelAndView("redirect:/login");
}

10. Form submission and validation

Bind form fields with @ModelAttribute and validate using BindingResult:

@Controller
public class RegistrationController {
    @RequestMapping(value="/doRegister", method=RequestMethod.POST)
    public String doRegister(@ModelAttribute("userForm") User user, BindingResult result) {
        if (result.hasErrors()) {
            // handle errors
        } else {
            // process registration
        }
        return "Success";
    }
}

11. Handling file uploads

Accept uploaded files as CommonsMultipartFile[] and transfer them to the server:

@RequestMapping(value="/uploadFiles", method=RequestMethod.POST)
public String handleFileUpload(@RequestParam CommonsMultipartFile[] fileUpload) throws Exception {
    for (CommonsMultipartFile aFile : fileUpload) {
        aFile.transferTo(new File(aFile.getOriginalFilename()));
    }
    return "Success";
}

12. Autowiring business classes

Inject service or DAO beans into controllers with @Autowired:

@Controller
public class UserController {
    @Autowired
    private UserDAO userDAO;

    public String listUser() { userDAO.list(); }
    public String saveUser(User user) { userDAO.save(user); }
    public String deleteUser(User user) { userDAO.delete(user); }
    public String getUser(int userId) { userDAO.get(userId); }
}

13. Accessing HttpServletRequest and HttpServletResponse

Simply add the request or response objects as method parameters; Spring will inject them automatically.

@RequestMapping("/download")
public String doDownloadFile(HttpServletRequest request, HttpServletResponse response) {
    // use request/response
    return "DownloadPage";
}

14. Following the Single Responsibility Principle

Controllers should delegate business logic to service/DAO layers, keeping the controller focused on request handling and workflow orchestration.