Model, View, and ModelAndView

Introduction

A controller method rarely just does something and returns nothing - it usually needs to hand data to a page for rendering, whether that is a list of products, a logged-in user's name, or an error message. In Spring MVC, that hand-off happens through the Model. In this lesson, you will learn how to put data into the Model, how a returned String becomes a rendered page, and how ModelAndView bundles both concerns into a single return value.

The MVC Flow, Revisited

Recall the Model-View-Controller pattern: the Controller receives the request and decides what needs to happen, the Model holds the data the response will be built from, and the View is the template that renders that data into HTML (or another format). A handler method's job is to populate the Model and then say which View should render it.

Adding Data with Model

Spring will inject a Model object into any handler method that declares it as a parameter. You add data with addAttribute(name, value), and that name becomes the variable the view template can reference.

@GetMapping("/profile")
public String profile(Model model) {
    model.addAttribute("username", "asha92");
    model.addAttribute("joinYear", 2023);
    return "profile"; // resolves to templates/profile.html
}

In a Thymeleaf template, that data is now available as ${username} and ${joinYear}. The Model is essentially a bridge - the controller fills it, the view template reads from it.

Returning a View Name

The String returned from a @Controller method (without @ResponseBody) is treated as a logical view name, not raw text sent to the browser. A ViewResolver bean turns that logical name into an actual template file, typically by adding a configured prefix and suffix.

spring.mvc.view.prefix=/WEB-INF/views/
spring.mvc.view.suffix=.jsp

Using ModelAndView

Sometimes it is convenient to set both the view name and the model data in one object rather than two separate things. ModelAndView bundles them together, and a handler method can return it directly instead of taking a Model parameter and returning a String.

@GetMapping("/dashboard")
public ModelAndView dashboard() {
    ModelAndView mav = new ModelAndView("dashboard");
    mav.addObject("visits", 128);
    mav.addObject("lastLogin", LocalDate.now());
    return mav;
}

Both styles - Model plus a returned view name, or a single ModelAndView - produce the exact same result. Most modern Spring MVC code favors the Model-plus-String style because it is slightly less verbose and easier to unit test.

Redirects and Forwards

A returned view name can also start with a special prefix that changes how it is handled. redirect: tells the browser to issue a brand new GET request to a different URL (useful after a successful form POST, to avoid duplicate submissions). forward: hands the request to another handler internally without a new round trip to the browser.

@PostMapping("/books/add")
public String addBook(@RequestParam String title) {
    bookService.save(title);
    return "redirect:/books/list"; // browser makes a new GET request
}

Common Mistakes

Best Practices

Frequently Asked Questions

Key Takeaways

Summary

Model and view names are how controllers hand finished data over to the presentation layer. Next, you will flip the direction and see how data flows the other way - from an HTML form submitted by the user, back into a Java object your controller can work with.