HTTP Response Status Codes

• 3-digit numbers returned by a server.
• Represent the execution status or outcome of an HTTP request.
• Always provided by the web server or web application after processing a request.

Category	Code Range	Meaning
1xx	100–199	Informational
2xx	200–299	Success
3xx	300–399	Redirection
4xx	400–499	Client Error
5xx	500–599	Server Error

Common Codes

Code	Meaning	Description
100	Continue	Request received, continue.
101	Switching Protocols	Protocol change accepted.
102	Processing	Request in progress.
200	OK	Request succeeded.
201	Created	New resource created.
202	Accepted	Request accepted for processing, but not completed yet.
204	No Content	Success, no body returned.
301	Moved Permanently	Resource moved to new URL.
302	Found	Temporary redirect.
304	Not Modified	Cached version still valid.
400	Bad Request	Invalid syntax.
401	Unauthorized	Authentication needed.
403	Forbidden	Access denied.
404	Not Found	Resource doesn’t exist.
405	Method Not Allowed	HTTP method not supported for the resource.
500	Internal Server Error	General server error.
503	Service Unavailable	Server overloaded or down.

Difference Between 204 and 404

Status Code	Meaning	When Used	Response Body
204 No Content	Request succeeded, but there’s no content to return.	When the server successfully processes a request, but doesn’t need to send any data back (e.g., DELETE success, or empty result set).	No body
404 Not Found	The requested resource doesn’t exist on the server.	When the client asks for a resource (URL) that’s not found or invalid.	No body (or optional error message)

Example - 204 → "User deleted successfully, no data to return."
- 404 → "User not found in the system."

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ResponseEntity in Spring

• Represents the whole HTTP response.
• Used to control status code, headers, and body in a REST API response.
• Belongs to package: org.springframework.http.
• Structure : ResponseEntity<T>

@RequestMapping(path = "/user/v2", method = RequestMethod.POST, consumes = MediaType.APPLICATION_JSON_VALUE)
    public ResponseEntity<String> createUser2(@RequestBody UserRequest userRequest) {

        String msg = userService.CreateUser(userRequest);

        if (msg.equals("User Created Succesfully..")) {
            // return new ResponseEntity<String>(msg, HttpStatusCode.valueOf(201));
            return ResponseEntity.status(HttpStatus.CREATED).body(msg);
        }
        // return new ResponseEntity<String>(msg, HttpStatusCode.valueOf(200));
        // return ResponseEntity.ok(msg);
        return ResponseEntity.status(HttpStatus.OK).body(msg);
    }

 return ResponseEntity.ok(msg);
 return new ResponseEntity<String>(msg, HttpStatusCode.valueOf(200));

 return ResponseEntity.noContent().build();
 return new ResponseEntity<String>(null, HttpStatusCode.valueOf(204));

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