Hello REST API with Spring Boot

Before you start

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

Exercise 1 - Hello REST API

Goal: Understand what a REST endpoint is, what JSON looks like, and how Spring serializes objects.

1. Create a new class named HelloController, and add the GET /api/hello endpoint that returns JSON:

   {
       "message": "Hello, World!",
       "timestamp": "2026-01-28T10:00:00"
   }

   Replace the timestamp value with the current date and time, by using LocalDateTime.now().

   Hint: Use a Map<String, Object> to create the JSON response.

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

3. In the same class, add another GET endpoint /api/greet/{name} that takes a path variable name and returns a JSON response:

   {
       "message": "Hello, {name}!",
       "timestamp": "2026-01-28T10:00:00"
   }

   Replace {name} with the actual name provided in the URL and the timestamp value with the current date and time.

4. Test the endpoint using your browser or Postman by navigating to http://localhost:8080/api/greet/YourName. Replace YourName with any name you choose.

5. Add a GET /api/echo?text=... returning the text provided as a query parameter:

   {
       "echo": "Your text here"
   }

   Replace Your text here with the actual text provided in the query parameter and the timestamp value with the current date and time.

6. Test the endpoint using your browser or Postman by navigating to http://localhost:8080/api/echo?text=Hello.

7. Instead of using a HashMap, create a new class named GreetingResponse with fields message and timestamp. Modify the /api/hello and /api/greet/{name} endpoints to return instances of GreetingResponse instead of a HashMap.