@GetMapping for GET requests in Spring Boot - Step-by-Step Execution

Concept Flow - @GetMapping for GET requests

Client sends GET request

↓

Spring Boot matches URL

↓

@GetMapping method called

↓

Method executes and returns data

↓

Spring Boot sends response back to client

This flow shows how a GET request from a client is handled by a Spring Boot controller method annotated with @GetMapping, which returns data back to the client.

Execution Sample

Spring Boot

@GetMapping("/hello")
public String sayHello() {
    return "Hello, World!";
}

This code defines a method that handles GET requests to '/hello' and returns a greeting string.

Execution Table

Step	Action	Input/Condition	Result/Output
1	Client sends GET request	GET /hello	Request received by Spring Boot
2	Spring Boot matches URL	URL = /hello	Matches @GetMapping("/hello") method
3	Call method sayHello()	No parameters	Method executes
4	Method returns	Return value = "Hello, World!"	Response body set to "Hello, World!"
5	Spring Boot sends response	Response body = "Hello, World!"	Client receives "Hello, World!"
6	End	No more actions	Request handling complete

💡 Request handled successfully and response sent back to client

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
requestUrl	null	/hello	/hello	/hello
methodReturnValue	null	null	"Hello, World!"	"Hello, World!"

Key Moments - 3 Insights

Why does the method execute only for GET requests?

Because @GetMapping specifically maps HTTP GET requests to the method, as shown in execution_table step 2 where Spring Boot matches the URL and HTTP method.

What happens if the URL does not match any @GetMapping?

Spring Boot will not call the method and will return a 404 Not Found error, since no matching handler is found.

Can the method return other types besides String?

Yes, the method can return objects, which Spring Boot converts to JSON automatically if annotated properly.

Visual Quiz - 3 Questions

Look at the execution table, what is the methodReturnValue after step 4?

A "Hello, World!"

B null

C /hello

D GET /hello

💡 Hint

Check the variable_tracker row for methodReturnValue at After Step 4

At which step does Spring Boot match the URL to the @GetMapping method?

A Step 1

B Step 2

C Step 3

D Step 5

💡 Hint

Look at the execution_table Action column for URL matching

If the client sends a POST request instead of GET, what happens?

A The method returns "Hello, World!"

B The @GetMapping method is called anyway

C Spring Boot returns 404 Not Found

D The server crashes

💡 Hint

Refer to key_moments about URL and method matching

Concept Snapshot

@GetMapping maps HTTP GET requests to controller methods.
Use @GetMapping("/path") above a method to handle GET requests to that path.
The method runs when a matching GET request arrives.
Return values become the response body.
If no match, Spring Boot returns 404.
Works for simple strings or objects (auto JSON).

Full Transcript

When a client sends a GET request to a Spring Boot server, the framework looks for a method annotated with @GetMapping that matches the request URL. If found, it calls that method. The method runs and returns a value, such as a string. Spring Boot then sends this value back as the response body to the client. If no matching method is found, the server returns a 404 error. This process ensures that GET requests are handled cleanly and simply by methods marked with @GetMapping.