Building a Web Application with MVC Design Patterns

Using Java and Spring MVC to Create a Scalable and Maintainable To-Do List Manager

Introduction

To-do lists are an essential tool for managing our daily tasks and increasing productivity. With the advent of web technologies, it has become easier to create web applications that allow users to create and manage to-do lists. In this article, we will learn how to create a web application that allows users to create and manage to-do lists using appropriate design patterns.

I would also recommend reading this article on designing scalable software architecture.

Design Patterns

Design patterns are reusable solutions to common software design problems. They provide a standard way to solve a particular problem and help in creating maintainable and scalable software. In this article, we will use the Model-View-Controller (MVC) architectural pattern to implement the web application.

MVC Pattern

The MVC pattern separates the application into three interconnected components: the model, the view, and the controller. The model represents the data and business logic of the application. The view is responsible for displaying the data to the user. The controller handles user input and communicates with the model and view to update and display data, respectively.

Implementation

We will implement the web application using Java and the Spring MVC framework. The Spring MVC framework provides a powerful and flexible way to create web applications using the MVC pattern.

Step 1: Define the Model

The first step is to define the data model for the to-do lists and items. In this case, we can define two classes: ToDoList and ToDoItem. The ToDoList class contains a list of ToDoItem objects.

public class ToDoItem {
    private String description;
    private LocalDate dueDate;
    private boolean isComplete;

    // constructors, getters, and setters
}

public class ToDoList {
    private String name;
    private List<ToDoItem> items;

    // constructors, getters, and setters
}

Step 2: Implement the View

The next step is to implement the view, which is responsible for displaying the data to the user. In this case, we can use HTML and CSS to create a simple user interface that allows users to create new to-do lists, add new items to a to-do list, and mark items as complete.

<!DOCTYPE html>
<html>
<head>
    <title>ToDo Lists</title>
</head>
<body>
    <h1>My ToDo Lists</h1>
    <ul>
        <!-- loop through each ToDoList and display the name and items -->
        <li>
            <h2>ToDo List Name</h2>
            <ul>
                <li>Item 1</li>
                <li>Item 2</li>
                <li>Item 3</li>
            </ul>
        </li>
    </ul>

    <h2>Create New ToDo List</h2>
    <form method="POST" action="/todo-lists">
        <label for="name">Name:</label>
        <input type="text" name="name" id="name">
        <button type="submit">Create</button>
    </form>

    <h2>Add Item to ToDo List</h2>
    <form method="POST" action="/todo-lists/{list-id}/items">
        <label for="description">Description:</label>
        <input type="text" name="description" id="description">
        <label for="due-date">Due Date:</label>
        <input type="date" name="due-date" id="due-date">
        <button type="submit">Add</button>
    </form>
</body>
</html>

Step 3: Implement the Controller

The final step is to implement the controller, which handles user input and communicates with the model and view to update and display data. We will use the Spring MVC framework to create the controller.

@Controller
@RequestMapping("/todo-lists")
public class ToDoListController {
    private final ToDoListService toDoListService;

    @Autowired
    public ToDoListController(ToDoListService toDoListService) {
        this.toDoListService = toDoListService;
    }

    @GetMapping
    public String showToDoLists(Model model) {
        List<ToDoList> toDoLists = toDoListService.getAllToDoLists();
        model.addAttribute("toDoLists", toDoLists);
        return "to-do-lists";
    }

    @PostMapping
    public String createToDoList(@RequestParam String name) {
        ToDoList toDoList = new ToDoList(name);
        toDoListService.saveToDoList(toDoList);
        return "redirect:/todo-lists";
    }

    @PostMapping("/{listId}/items")
    public String createToDoItem(@PathVariable Long listId, @RequestParam String description, @RequestParam LocalDate dueDate) {
        ToDoItem toDoItem = new ToDoItem(description, dueDate, false);
        toDoListService.addItemToList(listId, toDoItem);
        return "redirect:/todo-lists";
    }

    @PostMapping("/{listId}/items/{itemId}")
    public String markToDoItemComplete(@PathVariable Long listId, @PathVariable Long itemId) {
        toDoListService.markItemComplete(listId, itemId);
        return "redirect:/todo-lists";
    }
}

The ToDoListController class is annotated with @Controller to indicate that it is a Spring MVC controller. The @RequestMapping annotation specifies the base URL for all requests handled by the controller. The ToDoListService dependency is injected using the @Autowired annotation.

The showToDoLists() method handles GET requests to the base URL and retrieves all to-do lists from the service layer. The Model object is used to pass the data to the view, which is rendered using the to-do-lists.html template.

The createToDoList() method handles POST requests to create a new to-do list. The @RequestParam annotation is used to retrieve the name of the new to-do list from the request parameters. A new ToDoList object is created and saved to the database using the service layer. Finally, the user is redirected to the base URL.

The createToDoItem() method handles POST requests to add a new item to a to-do list. The @PathVariable annotation is used to retrieve the ID of the to-do list from the URL. The @RequestParam annotations are used to retrieve the description and due date of the new item from the request parameters. A new ToDoItem object is created and added to the to-do list using the service layer. Finally, the user is redirected to the base URL.

The markToDoItemComplete() method handles POST requests to mark an item as complete. The @PathVariable annotations are used to retrieve the IDs of the to-do list and item from the URL. The service layer is used to mark the item as complete. Finally, the user is redirected to the base URL.

Conclusion

In this article, we learned how to create a web application that allows users to create and manage to-do lists using appropriate design patterns. We used the Model-View-Controller (MVC) pattern to separate the application into three interconnected components: the model, the view, and the controller. We used Java and the Spring MVC framework to implement the web application, and we created a simple user interface using HTML and CSS. Finally, we implemented the controller layer to handle user input and communicate with the model and view.

By following these best practices and design patterns, we have created a scalable and maintainable web application that can be easily extended and modified in the future. In addition, we have implemented a separation of concerns that promotes modularity and reduces coupling between components, making the application more flexible and easier to test.

Thank you 🙂