Returning different status codes in Spring Boot - Mini Project: Build & Apply

Returning different status codes in Spring Boot

📖 Scenario: You are building a simple web service that responds to client requests with different HTTP status codes depending on the input.This is common in real-world APIs to indicate success, errors, or other conditions.

🎯 Goal: Create a Spring Boot controller that returns different HTTP status codes based on the request parameter.You will learn how to send 200 OK, 400 Bad Request, and 404 Not Found responses.

📋 What You'll Learn

Create a Spring Boot controller class named StatusController

Add a GET endpoint at /check that accepts a query parameter code

Return 200 OK with body "Success" if code is 200

Return 400 Bad Request with body "Bad Request" if code is 400

Return 404 Not Found with body "Not Found" if code is 404

💡 Why This Matters

🌍 Real World

APIs often need to respond with different HTTP status codes to indicate success or errors clearly to clients.

💼 Career

Understanding how to return proper HTTP status codes is essential for backend developers working with RESTful services.

1

Create the controller class and method

Create a Spring Boot controller class named StatusController with a method checkStatus mapped to GET /check that accepts a query parameter code of type int.

Spring Boot

@RestController
public class StatusController {
    // Your code here
}

Hint

Use @RestController on the class and @GetMapping("/check") on the method.

Use @RequestParam int code to get the query parameter.

2

Add variables for response messages

Inside the checkStatus method, create three String variables named successMessage, badRequestMessage, and notFoundMessage with values "Success", "Bad Request", and "Not Found" respectively.

Spring Boot

@RestController
public class StatusController {
    @GetMapping("/check")
    public ResponseEntity checkStatus(@RequestParam int code) {
        // Define response messages
        // Your code here
    }
}

Hint

Declare three String variables with the exact names and values given.

3

Add logic to return different status codes

Inside the checkStatus method, add an if-else block that returns ResponseEntity with 200 OK and successMessage if code == 200, 400 Bad Request and badRequestMessage if code == 400, and 404 Not Found and notFoundMessage if code == 404.

Spring Boot

@RestController
public class StatusController {
    @GetMapping("/check")
    public ResponseEntity checkStatus(@RequestParam int code) {
        String successMessage = "Success";
        String badRequestMessage = "Bad Request";
        String notFoundMessage = "Not Found";
        // Add if-else logic to return ResponseEntity with correct status and body
        // Your code here
    }
}

Hint

Use ResponseEntity.ok() for 200 OK.

Use ResponseEntity.status(HttpStatus.BAD_REQUEST).body() for 400.

Use ResponseEntity.status(HttpStatus.NOT_FOUND).body() for 404.

4

Add import statements for annotations and classes

Add the necessary import statements for @RestController, @GetMapping, @RequestParam, ResponseEntity, and HttpStatus at the top of the file.

Spring Boot

// Add import statements here

@RestController
public class StatusController {
    @GetMapping("/check")
    public ResponseEntity checkStatus(@RequestParam int code) {
        String successMessage = "Success";
        String badRequestMessage = "Bad Request";
        String notFoundMessage = "Not Found";
        if (code == 200) {
            return ResponseEntity.ok(successMessage);
        } else if (code == 400) {
            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(badRequestMessage);
        } else if (code == 404) {
            return ResponseEntity.status(HttpStatus.NOT_FOUND).body(notFoundMessage);
        } else {
            return ResponseEntity.status(HttpStatus.BAD_REQUEST).body("Invalid code");
        }
    }
}

Hint

Import all required Spring annotations and classes from org.springframework.web.bind.annotation and org.springframework.http.

Practice

1. In Spring Boot, which class is commonly used to return different HTTP status codes from a controller?

easy

A. ResponseEntity

B. HttpStatusCode

C. HttpResponse

D. StatusCode

Solution

1. Step 1: Understand the purpose of ResponseEntity

   ResponseEntity is a Spring class that allows you to control the HTTP status code, headers, and body of the response.

2. Step 2: Identify the correct class for status codes

   HttpStatusCode, HttpResponse, and StatusCode are not standard Spring Boot classes for returning responses with status codes.

3. Final Answer:

   ResponseEntity -> Option A

4. Quick Check:

   Use ResponseEntity to return status codes [OK]

Hint: Use ResponseEntity to set status codes easily [OK]

Common Mistakes:

• Confusing ResponseEntity with HttpStatusCode
• Trying to return status codes without ResponseEntity
• Using non-existent classes like HttpResponse

2. Which of the following is the correct way to return a 404 Not Found status with a message in a Spring Boot controller?

easy

A. return new ResponseEntity("Not Found", 404);

B. return new ResponseEntity<>("Not Found", 404);

C. return ResponseEntity.status(404).body("Not Found");

D. return ResponseEntity(HttpStatus.NOT_FOUND, "Not Found");

Solution

1. Step 1: Check the syntax for ResponseEntity with status and body

   The method ResponseEntity.status(404).body("Not Found") correctly sets the status and body.

2. Step 2: Identify incorrect syntax options

   B uses a constructor with an int 404 instead of HttpStatus.NOT_FOUND. C uses an int instead of HttpStatus enum. D is not a valid constructor call.

3. Final Answer:

   return ResponseEntity.status(404).body("Not Found"); -> Option C

4. Quick Check:

   Use ResponseEntity.status().body() for custom status [OK]

Hint: Use ResponseEntity.status(code).body(message) [OK]

Common Mistakes:

• Using int instead of HttpStatus enum
• Incorrect constructor usage
• Missing method chaining for status and body

3. What will be the HTTP status code returned by this Spring Boot controller method?

public ResponseEntity<String> getUser(boolean found) {
    if (found) {
        return ResponseEntity.ok("User found");
    } else {
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body("User not found");
    }
}

medium

A. 404 if found is true, 200 if false

B. Always 404

C. Always 200

D. 200 if found is true, 404 if false

Solution

1. Step 1: Analyze the if condition

   If found is true, the method returns ResponseEntity.ok("User found"), which means HTTP 200.

2. Step 2: Analyze the else condition

   If found is false, it returns ResponseEntity.status(HttpStatus.NOT_FOUND).body("User not found"), which means HTTP 404.

3. Final Answer:

   200 if found is true, 404 if false -> Option D

4. Quick Check:

   ResponseEntity.ok = 200, status(HttpStatus.NOT_FOUND) = 404 [OK]

Hint: ResponseEntity.ok = 200, status(HttpStatus.NOT_FOUND) = 404 [OK]

Common Mistakes:

• Mixing up true/false branches
• Assuming default status 200 always
• Confusing status codes with messages

4. Identify the error in this Spring Boot controller method that tries to return a 201 Created status:

public ResponseEntity<String> createItem() {
    return new ResponseEntity<>("Item created", 201);
}

medium

A. Cannot return ResponseEntity with a String body

B. Using int 201 instead of HttpStatus enum

C. ResponseEntity constructor requires three arguments

D. Missing @ResponseBody annotation

Solution

1. Step 1: Check ResponseEntity constructor parameters

   The constructor expects a body and an HttpStatus enum, not an int.

2. Step 2: Identify the incorrect use of status code

   Passing 201 as int causes a compilation error; should use HttpStatus.CREATED instead.

3. Final Answer:

   Using int 201 instead of HttpStatus enum -> Option B

4. Quick Check:

   Use HttpStatus.CREATED, not int 201 [OK]

Hint: Use HttpStatus enum, not int, for status codes [OK]

Common Mistakes:

• Passing int instead of HttpStatus enum
• Forgetting to import HttpStatus
• Assuming String body is invalid

5. You want to create a Spring Boot controller method that returns 201 Created when a new user is successfully added, 400 Bad Request if the input is invalid, and 401 Unauthorized if the user is not logged in. Which code snippet correctly implements this behavior?

hard

A. public ResponseEntity<String> addUser(boolean validInput, boolean loggedIn) {
if (!loggedIn) {
return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body("Unauthorized");
}
if (!validInput) {
return ResponseEntity.status(HttpStatus.BAD_REQUEST).body("Invalid input");
}
return ResponseEntity.status(HttpStatus.CREATED).body("User created");
}

B. public ResponseEntity<String> addUser(boolean validInput, boolean loggedIn) {
if (!validInput) {
return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body("Unauthorized");
}
if (!loggedIn) {
return ResponseEntity.status(HttpStatus.BAD_REQUEST).body("Invalid input");
}
return ResponseEntity.status(HttpStatus.CREATED).body("User created");
}

C. public ResponseEntity<String> addUser(boolean validInput, boolean loggedIn) {
if (!loggedIn) {
return new ResponseEntity<>("Unauthorized", 401);
}
if (!validInput) {
return new ResponseEntity<>("Invalid input", 400);
}
return new ResponseEntity<>("User created", 201);
}

D. }
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Solution

1. Step 1: Verify correct use of HttpStatus enums

   public ResponseEntity<String> addUser(boolean validInput, boolean loggedIn) { if (!loggedIn) { return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body("Unauthorized"); } if (!validInput) { return ResponseEntity.status(HttpStatus.BAD_REQUEST).body("Invalid input"); } return ResponseEntity.status(HttpStatus.CREATED).body("User created"); } uses HttpStatus.UNAUTHORIZED, HttpStatus.BAD_REQUEST, and HttpStatus.CREATED enums correctly.

2. Step 2: Check logical order and syntax

   This code checks !loggedIn first, then !validInput, then returns 201. Options B, C, and D misuse status codes or pass ints to constructors instead of using HttpStatus enums.

3. Final Answer:

   Uses HttpStatus enums with correct logic: !loggedIn (401), !validInput (400), then 201 -> Option A

4. Quick Check:

   Use HttpStatus enums and correct logic order [OK]

Hint: Check login first, then input, use HttpStatus enums [OK]

Common Mistakes:

• Passing int status codes instead of HttpStatus enums
• Mixing up 400 and 401 status codes
• Incorrect order of condition checks