Request mapping by method and path in Spring Boot - Step-by-Step Execution

Concept Flow - Request mapping by method and path

Client sends HTTP request

↓

Spring Boot Dispatcher

↓

Check HTTP method (GET, POST, etc.)

↓

Match request path to @RequestMapping path

↓

Call matching controller method

↓

Return response to client

Spring Boot listens for HTTP requests, matches the method and path to controller methods annotated with @RequestMapping, then runs the matched method.

Execution Sample

Spring Boot

@RestController
@RequestMapping("/api")
public class MyController {
  @GetMapping("/hello")
  public String sayHello() {
    return "Hello";
  }
}

Defines a controller that responds to GET requests at path /api/hello with "Hello".

Execution Table

Step	HTTP Method	Request Path	Match @RequestMapping	Controller Method Called	Response
1	GET	/api/hello	Matches class @RequestMapping("/api") and method @GetMapping("/hello")	sayHello()	"Hello"
2	POST	/api/hello	Matches class @RequestMapping("/api") but no POST method for /hello	None	404 Not Found
3	GET	/api/goodbye	Matches class @RequestMapping("/api") but no GET method for /goodbye	None	404 Not Found

💡 Execution stops after matching request method and path or returning 404 if no match.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
HTTP Method	None	GET	POST	GET
Request Path	None	/api/hello	/api/hello	/api/goodbye
Matched Controller Method	None	sayHello()	None	None
Response	None	"Hello"	404 Not Found	404 Not Found

Key Moments - 2 Insights

Why does a POST request to /api/hello return 404 even though the path matches?

Because the controller only has a GET method mapped for /hello, no POST method exists. See execution_table row 2.

How does Spring Boot combine class-level and method-level @RequestMapping paths?

It joins the class-level path (/api) with the method-level path (/hello) to form the full path (/api/hello). See execution_table row 1.

Visual Quiz - 3 Questions

Look at the execution table, what response is returned for a GET request to /api/hello?

A 404 Not Found

B "Hello"

C 500 Internal Server Error

D Empty response

💡 Hint

Check execution_table row 1 under Response column.

At which step does the request method not match any controller method?

A Step 1

B Step 3

C Step 2

D None

💡 Hint

Look at execution_table rows 2 and 3 for method matching.

If you add a @PostMapping("/hello") method, what changes in the execution table?

A Step 2 would call the new method and return a response instead of 404

B Step 1 would change response

C Step 3 would match the new method

D No changes

💡 Hint

Adding a POST method for /hello affects POST requests at that path (see Step 2).

Concept Snapshot

Use @RequestMapping or shortcut annotations (@GetMapping, @PostMapping) to map HTTP methods and paths.
Class-level @RequestMapping sets a base path.
Method-level mappings add to the base path.
Spring matches incoming requests by method and path to call the right controller method.
If no match, returns 404 Not Found.

Full Transcript

In Spring Boot, you map HTTP requests to controller methods using @RequestMapping and its shortcuts like @GetMapping. The class-level @RequestMapping sets a base path, and method-level annotations add to it. When a request comes in, Spring checks the HTTP method and path to find the matching method. If found, it runs that method and returns the response. If not, it returns 404. For example, a GET request to /api/hello matches a method annotated with @GetMapping("/hello") inside a class annotated with @RequestMapping("/api"). A POST request to the same path returns 404 if no POST method exists. This flow ensures your app responds correctly to different HTTP methods and paths.