POST with a Request Body

GET reads, POST creates

A GET request asks for data (show me the products). A POST request sends data to be saved (here is a new product). For POST you use @PostMapping, and you read the sent data with @RequestBody.

Receive JSON as an object

When the client sends JSON, @RequestBody tells Spring to convert that JSON into a Java object — the reverse of last lesson:

@RestController
public class ProductController {

    @PostMapping("/products")
    public String create(@RequestBody Product product) {
        // here you would save it to a database (Unit 3)
        return "Created: " + product.getName()
             + " (price " + product.getPrice() + ")";
    }
}

How to test a POST

You cannot send a POST by just typing a URL in the browser (that sends a GET). Use a tool like Postman, the VS Code REST Client, or curl:

curl -X POST http://localhost:8080/products \
  -H "Content-Type: application/json" \
  -d "{\"id\":3,\"name\":\"Monitor\",\"price\":12999.0}"

The whole POST flow, step by step

Here is the complete journey of one POST request, from your tool to the response — read it in order so you can picture exactly what happens:

1. You (or a front-end) send a POST request to /products with a JSON body, e.g. {"id":3,"name":"Monitor","price":12999.0}.
2. Spring sees the method is POST and the path is /products, so it picks the method marked @PostMapping("/products").
3. Because the parameter has @RequestBody, Spring reads the JSON body and converts it into a Product object (it matches the JSON keys to the field names).
4. Your method runs with that ready-made product object, so product.getName() gives "Monitor".
5. The method returns a value (here a text message), and Spring sends it back to the client as the response.