Implement Create Task List

Watch Code

Now that we can list task lists, let's implement the ability to create new ones. We'll need to add methods to both our service and controller layers to handle this functionality.

Updating the Service Interface

First, let's add the create method to our TaskListService interface:

public interface TaskListService {
    List<TaskList> listTaskLists();
    TaskList createTaskList(TaskList taskList);  // Add this method
}

Implementing the Service Method

Now let's implement the create functionality in TaskListServiceImpl:

@Service
public class TaskListServiceImpl implements TaskListService {

    private final TaskListRepository taskListRepository;

    public TaskListServiceImpl(TaskListRepository taskListRepository) {
        this.taskListRepository = taskListRepository;
    }

    @Override
    public TaskList createTaskList(TaskList taskList) {
        if (null != taskList.getId()) {
            throw new IllegalArgumentException("Task list already has an ID!");
        }

        if (null == taskList.getTitle() || taskList.getTitle().isBlank()) {
            throw new IllegalArgumentException("Task list title must be present!");
        }

        LocalDateTime now = LocalDateTime.now();
        return taskListRepository.save(new TaskList(
                null,
                taskList.getTitle(),
                taskList.getDescription(),
                null,
                now,
                now
        ));
    }
}

Let's examine the key aspects of this implementation:

Input Validation:
- Checks that the task list doesn't already have an ID (it's a new task list)
- Ensures the title is not null or blank
Timestamp Handling:
- Sets both created and updated timestamps to the current time
- This ensures consistent timestamp creation
Clean Creation:
- Creates a new TaskList instance rather than using the input directly
- Ensures no unexpected data gets persisted
- Sets tasks to null as new lists start empty

Updating the Controller

Finally, let's add the create endpoint to our TaskListController:

@RestController
@RequestMapping(path = "/task-lists")
public class TaskListController {

    private final TaskListService taskListService;
    private final TaskListMapper taskListMapper;

    public TaskListController(TaskListService taskListService, TaskListMapper taskListMapper) {
        this.taskListService = taskListService;
        this.taskListMapper = taskListMapper;
    }

    @PostMapping
    public TaskListDto createTaskList(@RequestBody TaskListDto taskListDto) {
        TaskList createdTaskList = taskListService.createTaskList(
                taskListMapper.fromDto(taskListDto)
        );
        return taskListMapper.toDto(createdTaskList);
    }
}

Let's break down the new controller method:

Annotation:
- @PostMapping maps this to HTTP POST requests
- @RequestBody tells Spring to deserialize the request body into a TaskListDto
Implementation:
- Converts the incoming DTO to an entity using our mapper
- Calls the service to create the task list
- Converts the result back to a DTO for the response

How It Works Together

When a POST request arrives at /task-lists:

Spring deserializes the JSON request body into a TaskListDto
The controller converts the DTO to a TaskList entity
The service validates the input and creates a new TaskList
The repository persists the TaskList to the database
The controller converts the saved entity back to a DTO
Spring serializes the DTO to JSON for the response

Note that if validation fails, exceptions will be thrown. We'll handle these exceptions properly in the next lesson.

Testing the Endpoint

We can now create task lists through the frontend. The app will send a POST request with a JSON body like:

{
    "title": "My New List",
    "description": "A list of important tasks"
}

And receive a response like:

{
    "id": "123e4567-e89b-12d3-a456-426614174000",
    "title": "My New List",
    "description": "A list of important tasks",
    "count": 0,
    "progress": null,
    "tasks": null
}

Summary

Added create functionality to the TaskListService
Implemented input validation in the service layer
Added the POST endpoint to create task lists
Connected all layers for a complete create operation