Inside the Spring Boot Request Lifecycle for REST APIs

 In a Java Spring Boot application built with Maven and exposing REST APIs, here's what happens when you enter a URL that maps to a REST endpoint:

1. HTTP Request Initiation

Typing the API URL in your browser sends an HTTP GET request (by default), since browsers use GET when accessing URLs directly.

2. Request Mapping

Spring Boot uses annotations like @RestController and @GetMapping("/orders") to define endpoint mappings. The DispatcherServlet receives the incoming request and matches it against these mappings.

3. Controller Activation

Once matched, Spring invokes the relevant controller method (e.g., getAllOrders() in OrderController). If using prototype scope, a new bean instance is created for each request.

4. Service Layer Handling

The controller delegates processing to a @Service class. With Spring’s @Autowired annotation, dependencies like repositories or other services are injected automatically.

5. Business Logic Execution

The service layer executes the core business logic (e.g., fetching orders from a database). Spring handles transaction management behind the scenes, unless configured otherwise.

6. Response Construction

The service returns data, often wrapped in a ResponseEntity. Spring Boot automatically serializes the response (usually into JSON) using Jackson or other supported libraries.

7. Response Dispatch

The DispatcherServlet constructs the HTTP response using the ResponseEntity, including headers and status codes, and sends it to the client over HTTP.

8. Client-side Rendering

The browser receives the JSON response. You can then use JavaScript (or another frontend tool) to parse and display the data to users.