REST APIs›Core· 40 min read

GET Endpoints that Return JSON

Return a Java object or list from a controller and Spring turns it into JSON automatically — the heart of any API.

What you will learn

Return an object as JSON
Return a list as a JSON array
Understand automatic conversion

Why JSON?

JSON is the standard text format APIs use to send data. It looks like simple labelled values. The best part in Spring Boot: if your method returns a Java object, Spring converts it to JSON for you — you write zero conversion code.

Return an object

Make a small class to hold data, then return it from a controller method:

Returning a Product object from a GET endpoint

// A simple data class (a "model")
public class Product {
    private int id;
    private String name;
    private double price;

    public Product(int id, String name, double price) {
        this.id = id; this.name = name; this.price = price;
    }
    // getters are needed so Spring can read the fields
    public int getId() { return id; }
    public String getName() { return name; }
    public double getPrice() { return price; }
}

@RestController
public class ProductController {
    @GetMapping("/product")
    public Product one() {
        return new Product(1, "Keyboard", 799.0);
    }
}

Note: Output (visiting /product): {"id":1,"name":"Keyboard","price":799.0} Spring read the getters and turned the object into JSON automatically. The field names become the JSON keys.

Return a list

Return a List and Spring sends back a JSON array:

Returning a list of products

@GetMapping("/products")
public List<Product> all() {
    return List.of(
        new Product(1, "Keyboard", 799.0),
        new Product(2, "Mouse", 499.0)
    );
}

Note: Output (visiting /products): [{"id":1,"name":"Keyboard","price":799.0}, {"id":2,"name":"Mouse","price":499.0}] A Java List becomes a JSON array, and each Product becomes a JSON object inside it.

Tip: Spring needs getters to read your object’s fields. If your JSON comes back empty (just two curly braces), missing getters are almost always the reason.

Watch out: Do not put passwords or other secret fields on objects you return — whatever the object exposes through getters ends up in the JSON the client can see.

Q. You return a Java List of objects from a GET method. What does the client receive?

Answer: Spring converts a returned List into a JSON array automatically, turning each object inside it into a JSON object using its getters.

✍️ Practice

Create a Book class (id, title, author) and a /book endpoint that returns one.
Add a /books endpoint that returns a list of three books as JSON.

🏠 Homework

Build a /students endpoint that returns a list of student objects (id, name, course) as JSON.