@RequestMapping for base paths in Spring Boot - Step-by-Step Execution

Concept Flow - @RequestMapping for base paths

Start Application

↓

Scan Controller Class

↓

Find @RequestMapping at Class Level

↓

Set Base Path for All Methods

↓

Scan Methods with @RequestMapping

↓

Combine Base Path + Method Path

↓

Handle Incoming HTTP Request

↓

Match Request URL to Combined Path

Yes No↓

Call Method

↓

Send Response

↓

End

The flow shows how Spring Boot reads a controller's base path from @RequestMapping on the class, then combines it with method-level paths to match incoming requests.

Execution Sample

Spring Boot

import org.springframework.web.bind.annotation.*;

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

This code sets a base path '/api' for all methods in MyController, so the full path for sayHello is '/api/hello'.

Execution Table

Step	Action	Details	Result
1	Start Application	Spring Boot starts and scans components	Application context initialized
2	Scan Controller Class	Find MyController class	Class found
3	Find @RequestMapping at Class Level	Reads '/api' base path	Base path set to '/api'
4	Scan Methods with @RequestMapping	Find sayHello method with @GetMapping('/hello')	Method path '/hello' found
5	Combine Base Path + Method Path	Combine '/api' + '/hello'	Full path '/api/hello'
6	Handle Incoming HTTP Request	Request to GET '/api/hello'	Request received
7	Match Request URL to Combined Path	Check if '/api/hello' matches	Match found
8	Call Method	Invoke sayHello()	Returns 'Hello'
9	Send Response	Send 'Hello' back to client	Response sent
10	Request to GET '/hello'	Request received	No match, 404 returned

💡 Execution stops when request matches a combined path or returns 404 if no match.

Variable Tracker

Variable	Start	After Step 3	After Step 5	After Step 7	Final
basePath	null	"/api"	"/api"	"/api"	"/api"
methodPath	null	null	"/hello"	"/hello"	"/hello"
fullPath	null	null	"/api/hello"	"/api/hello"	"/api/hello"
requestURL	null	null	null	"/api/hello" or "/hello"	"/api/hello" or "/hello"
matchFound	false	false	false	true or false	true or false

Key Moments - 3 Insights

Why does the method path '/hello' become '/api/hello'?

Because the class-level @RequestMapping sets a base path '/api' that prefixes all method paths, as shown in execution_table step 5.

What happens if a request comes to '/hello' without the base path?

The request does not match any combined path, so Spring returns a 404 error, as shown in execution_table step 10.

Can multiple methods share the same base path?

Yes, all methods in the controller share the base path from the class-level @RequestMapping, making it easier to organize URLs.

Visual Quiz - 3 Questions

Look at the execution_table, what is the full path after combining base and method paths at step 5?

A "/api"

B "/hello"

C "/api/hello"

D "/hello/api"

💡 Hint

Check the 'Result' column at step 5 in execution_table.

At which step does Spring decide the request matches the controller method?

A Step 4

B Step 7

C Step 9

D Step 10

💡 Hint

Look for 'Match found' in the 'Result' column of execution_table.

If the base path was changed to '/service', what would be the full path for sayHello method?

A "/service/hello"

B "/hello/service"

C "/api/hello"

D "/hello"

💡 Hint

Refer to variable_tracker 'basePath' and how it combines with 'methodPath'.

Concept Snapshot

@RequestMapping at class level sets a base URL path.
All method-level mappings append to this base path.
Incoming requests match combined paths.
If no match, Spring returns 404.
Use base paths to organize related endpoints.

Full Transcript

When a Spring Boot application starts, it scans controller classes for @RequestMapping annotations. If a class has @RequestMapping with a path like '/api', this path becomes the base for all methods inside. Each method can have its own @RequestMapping or shortcut like @GetMapping with a sub-path such as '/hello'. Spring combines the base path and method path to form the full URL, for example '/api/hello'. When a request comes in, Spring checks if the URL matches any combined path. If it matches, the corresponding method is called and its response is sent back. If no match is found, Spring returns a 404 error. This helps organize URLs by grouping related endpoints under a common base path.