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CRUD REST API with Spring Boot

In IntelliJ, create a new Spring Boot 4 project that uses JDK25 and Java 25 with the only dependency being Spring Web.

Exercise 1 - Nested JSON Response​

Goal: Learn how to create nested JSON responses using Java classes.

  1. Create a new class named Address with the following fields:

    • street (String)
    • city (String)
    • zipCode (String)

  2. Create another class named User with the following fields:

    • id (Long)
    • name (String)
    • email (String)
    • address (Address)

  3. Create a new class named UserController (make it a rest controller), add a new endpoint GET /api/users/{id} that returns a User object for the given id (the data can be hardcoded for this exercise). The JSON response should look like this:

    {
        "id": 1,
        "name": "John Doe",
        "email": "jd@ek.dk",
        "address": {
            "street": "Guldbergsgade 29",
            "city": "Copenhagen",
            "zipCode": "2200"
            }
    }

  4. Test the endpoint using your browser or Postman by navigating to http://localhost:8080/api/users/1.

Exercise 2 - List of Objects in JSON Response​

Goal: Learn how to return a list of objects in a JSON response.

  1. Create a list of User objects in the UserController.

  2. In the UserController, add a new endpoint GET /api/users that returns a list of User objects with sample data (at least 3 users), each containing a nested Address object.

    [
        {
            "id": 1,
            "name": "John Doe",
            "email": "jd@ek.dk",
            "address": {
                "street": "Guldbergsgade 29",
                "city": "Copenhagen",
                "zipCode": "2200"
            }
        },
        {
            "id": 2,
            "name": "Jane Smith",
            "email": "js@ek.dk",
            "address": {
                "street": "Amagerbrogade 100",
                "city": "Copenhagen",
                "zipCode": "2300"
            }
        }
    ]

  3. Test the endpoint using your browser or Postman by navigating to http://localhost:8080/api/users.

  4. Refactor the api/users/{id} endpoint to retrieve the user from the list based on the provided id. If the user is not found, return a 404 Not Found response.

    • Hint: Use a loop to find the user
    • Hint: Use ResponseEntity.notFound().build() for 404 responses

Exercise 3 - Bonus: Customize JSON output order​

Goal: Learn how to customize the order of fields in the JSON response.

  1. In the User class, use a Jackson annotation to specify the order of fields in the JSON output so that id comes first, followed by name, email, and then address.
    • Hint: Use the @JsonPropertyOrder({"id", "name", "email", "address"}) annotation on the User class.
  2. Test the /api/users and /api/users/{id} endpoints again to verify that the JSON output reflects the specified field order.
  3. (Optional) Apply similar ordering to the Address class.
  4. Test the endpoints again to verify the changes.

Exercise 4 - POST,PUT, DELETE Operations​

Goal: Fully implement CRUD operations for the User resource.

4.1 - POST endpoint​

  1. Create a new endpoint POST /api/users in the UserController that accepts a User object in the request body and returns the same user with a 201 Created status code. The ID should be auto-generated (you can simulate this by incrementing a static variable).
    • Hint: Use the @RequestBody annotation to bind the incoming JSON to a User object.
    • Hint: Use AtomicLong or Long for generating unique IDs.
  2. Test the endpoint using Postman by sending a POST request to http://localhost:8080/api/users with a JSON body representing a new user (without an ID). Verify that the response contains the created user with an assigned ID.
  3. Add a Location header to the response that points to the URL of the newly created user (e.g., /api/users/{id}).
    • Hint: You can use ResponseEntity.created(URI.create("/api/users/" + user.getId())).body(user) to set the Location header.

4.2 - PUT endpoint​

  1. Create a new endpoint PUT /api/users/{id} in the UserController that accepts a User` object in the request body and updates the existing user with the specified ID.
  2. If the user with the specified ID does not exist, return a 404 Not Found response.
  3. Test the endpoint using Postman by sending a PUT request to http://localhost:8080/api/users/{id} with a JSON body representing the updated user data. Verify that the response contains the updated user.

4.3 - DELETE endpoint​

  1. Create a new endpoint DELETE /api/users/{id} in the UserController that deletes the user with the specified ID and returns a 204 No Content status code.
  2. If the user with the specified ID does not exist, return a 204 No Content response.
  3. Test the endpoint using Postman by sending a DELETE request to http://localhost:8080/api/users/{id}. Verify that the response status code is 204 No Content.