Spring MVC

Spring MVC Architecture

Spring MVC is a web framework built on the Servlet API. It follows the Model-View-Controller pattern. The central component is the DispatcherServlet, which acts as a front controller — it receives all requests and delegates them to the appropriate handler (controller).

Request flow: Browser → DispatcherServlet → HandlerMapping → Controller → Service → Model → ViewResolver → View (JSP/Thymeleaf) → Response

Spring MVC Controller

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import javax.validation.Valid;

@Controller
@RequestMapping("/products")
public class ProductController {

    private final ProductService productService;

    public ProductController(ProductService productService) {
        this.productService = productService;
    }

    // GET /products - List all products
    @GetMapping
    public String listProducts(Model model) {
        model.addAttribute("products", productService.findAll());
        model.addAttribute("title", "Product List");
        return "products/list"; // View name: templates/products/list.html
    }

    // GET /products/{id} - Show product detail
    @GetMapping("/{id}")
    public String showProduct(@PathVariable Long id, Model model) {
        Product product = productService.findById(id);
        model.addAttribute("product", product);
        return "products/detail";
    }

    // GET /products/new - Show create form
    @GetMapping("/new")
    public String showCreateForm(Model model) {
        model.addAttribute("product", new Product());
        return "products/form";
    }

    // POST /products - Create product
    @PostMapping
    public String createProduct(@Valid @ModelAttribute Product product,
                                BindingResult result) {
        if (result.hasErrors()) {
            return "products/form"; // Return to form with errors
        }
        productService.save(product);
        return "redirect:/products"; // Post-Redirect-Get pattern
    }

    // GET /products/{id}/edit - Show edit form
    @GetMapping("/{id}/edit")
    public String showEditForm(@PathVariable Long id, Model model) {
        model.addAttribute("product", productService.findById(id));
        return "products/form";
    }

    // POST /products/{id} - Update product
    @PostMapping("/{id}")
    public String updateProduct(@PathVariable Long id,
                                @Valid @ModelAttribute Product product,
                                BindingResult result) {
        if (result.hasErrors()) return "products/form";
        product.setId(id);
        productService.save(product);
        return "redirect:/products/" + id;
    }

    // POST /products/{id}/delete - Delete product
    @PostMapping("/{id}/delete")
    public String deleteProduct(@PathVariable Long id) {
        productService.deleteById(id);
        return "redirect:/products";
    }
}

Request Mapping Annotations

Annotation	HTTP Method	Equivalent
`@RequestMapping`	Any	Base mapping
`@GetMapping`	GET	@RequestMapping(method=GET)
`@PostMapping`	POST	@RequestMapping(method=POST)
`@PutMapping`	PUT	@RequestMapping(method=PUT)
`@DeleteMapping`	DELETE	@RequestMapping(method=DELETE)
`@PatchMapping`	PATCH	@RequestMapping(method=PATCH)

Thymeleaf Template Example

<!-- templates/products/list.html -->
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <title th:text="${title}">Products</title>
</head>
<body>
    <h1 th:text="${title}">Product List</h1>

    <a th:href="@{/products/new}">Add New Product</a>

    <table>
        <thead>
            <tr><th>ID</th><th>Name</th><th>Price</th><th>Actions</th></tr>
        </thead>
        <tbody>
            <tr th:each="product : ${products}">
                <td th:text="${product.id}"></td>
                <td th:text="${product.name}"></td>
                <td th:text="${#numbers.formatCurrency(product.price)}"></td>
                <td>
                    <a th:href="@{/products/{id}(id=${product.id})}">View</a>
                    <a th:href="@{/products/{id}/edit(id=${product.id})}">Edit</a>
                    <form th:action="@{/products/{id}/delete(id=${product.id})}" method="post">
                        <button type="submit">Delete</button>
                    </form>
                </td>
            </tr>
        </tbody>
    </table>
</body>
</html>

@PathVariable, @RequestParam, @ModelAttribute

@Controller
public class BindingExamples {

    // @PathVariable: /users/42
    @GetMapping("/users/{id}")
    public String getUser(@PathVariable Long id, Model model) {
        model.addAttribute("user", userService.findById(id));
        return "user/detail";
    }

    // Multiple path variables: /orders/5/items/3
    @GetMapping("/orders/{orderId}/items/{itemId}")
    public String getOrderItem(@PathVariable Long orderId,
                               @PathVariable Long itemId, Model model) {
        model.addAttribute("item", orderService.getItem(orderId, itemId));
        return "order/item";
    }

    // @RequestParam: /search?q=java&page=1&size=10
    @GetMapping("/search")
    public String search(@RequestParam String q,
                         @RequestParam(defaultValue = "1") int page,
                         @RequestParam(defaultValue = "10") int size,
                         @RequestParam(required = false) String category,
                         Model model) {
        model.addAttribute("results", searchService.search(q, page, size, category));
        return "search/results";
    }

    // @ModelAttribute: binds form fields to object
    @PostMapping("/register")
    public String register(@ModelAttribute @Valid UserForm form,
                           BindingResult errors, Model model) {
        if (errors.hasErrors()) {
            return "auth/register";
        }
        userService.register(form);
        return "redirect:/login?registered=true";
    }
}

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Spring MVC

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