Implement Get Task List

Now that we can list and create task lists, let's implement the ability to retrieve a single task list by its ID.

This functionality is essential for viewing and editing individual task lists. We'll need to add methods to both our service and controller layers.

Updating the Service Interface

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

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

We're returning an Optional<TaskList> because the requested task list might not exist.

Implementing the Service Method

Now let's implement the get functionality in TaskListServiceImpl:

@Service
public class TaskListServiceImpl implements TaskListService {

    private final TaskListRepository taskListRepository;

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

    @Override
    public Optional<TaskList> getTaskList(UUID id) {
        return taskListRepository.findById(id);
    }
}

This implementation is straightforward:

Takes a UUID parameter representing the task list ID
Delegates directly to the repository's findById method
Returns an Optional<TaskList> which will be empty if no task list exists with that ID

Updating the Controller

Now let's add the get 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;
    }

    @GetMapping(path = "/{task_list_id}")
    public Optional<TaskListDto> getTaskList(
            @PathVariable("task_list_id") UUID taskListId) {
        return taskListService.getTaskList(taskListId)
                .map(taskListMapper::toDto);
    }
}

Let's break down the key components of this endpoint:

URL Path:
- @GetMapping(path = "/{task_list_id}") maps this to GET requests with a task list ID in the path
- The ID is captured as a path variable
Path Variable:
- @PathVariable("task_list_id") extracts the ID from the URL
- Spring automatically converts the string ID to a UUID
Implementation:
- Calls the service to get the task list
- Uses map to transform the TaskList to TaskListDto if present
- Returns an empty Optional if no task list is found

How It Works Together

When a GET request arrives at /task-lists/{id}:

Spring extracts the ID from the URL path
The controller calls taskListService.getTaskList()
The service delegates to taskListRepository.findById()
If found:
- The repository returns the TaskList entity
- The controller converts it to a DTO
- Spring serializes the DTO to JSON
If not found:
- An empty Optional is returned
- Spring converts this to a 200 OK with null body

For example, a GET request to /task-lists/123e4567-e89b-12d3-a456-426614174000 might return:

{
  "id": "123e4567-e89b-12d3-a456-426614174000",
  "title": "My Task List",
  "description": "Important tasks",
  "count": 2,
  "progress": 0.5,
  "tasks": [
    {
      "id": "789e4567-e89b-12d3-a456-426614174001",
      "title": "First Task",
      "description": "Do something important",
      "dueDate": "2024-11-01T09:00:00",
      "priority": "HIGH",
      "status": "OPEN"
    }
  ]
}

Summary

Added get functionality to the TaskListService
Implemented the get endpoint in the controller
Used Optional to handle cases where the task list isn't found
Connected all layers for a complete get operation
Maintained consistent error handling through our global exception handler