Custom response headers in Spring Boot - Mini Project: Build & Apply

Custom Response Headers in Spring Boot

📖 Scenario: You are building a simple Spring Boot web service that returns a greeting message. You want to add a custom response header to the HTTP response to provide extra information to the client.

🎯 Goal: Create a Spring Boot controller that returns a greeting message and includes a custom response header named X-Custom-Header with the value MyHeaderValue.

📋 What You'll Learn

Create a Spring Boot REST controller class named GreetingController.

Add a GET endpoint at /greet that returns a String greeting message.

Add a custom response header X-Custom-Header with the value MyHeaderValue to the HTTP response.

💡 Why This Matters

🌍 Real World

Custom response headers are often used to send extra information like security tokens, version info, or metadata from a server to a client in web applications.

💼 Career

Knowing how to add custom headers in Spring Boot is important for backend developers to control HTTP responses and improve API communication.

1

Create the GreetingController class

Create a public class named GreetingController annotated with @RestController.

Spring Boot

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

Hint

Use @RestController annotation above the class declaration.

2

Add a GET endpoint method

Inside GreetingController, add a public method named greet annotated with @GetMapping("/greet") that returns the String "Hello, World!".

Spring Boot

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;

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

Hint

Use @GetMapping("/greet") to map the method to the GET request path.

3

Add HttpServletResponse parameter

Modify the greet method to accept a parameter of type HttpServletResponse named response.

Spring Boot

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;
import jakarta.servlet.http.HttpServletResponse;

@RestController
public class GreetingController {
    @GetMapping("/greet")
    public String greet(HttpServletResponse response) {
        // Your code here
        return "Hello, World!";
    }
}

Hint

Add HttpServletResponse response as a parameter to the greet method.

4

Set the custom response header

Inside the greet method, use the response object to add a header named X-Custom-Header with the value MyHeaderValue before returning the greeting string.

Spring Boot

import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.bind.annotation.GetMapping;
import jakarta.servlet.http.HttpServletResponse;

@RestController
public class GreetingController {
    @GetMapping("/greet")
    public String greet(HttpServletResponse response) {
        // Add custom header here
        return "Hello, World!";
    }
}

Hint

Use response.addHeader("X-Custom-Header", "MyHeaderValue") to add the header.

Practice

1. What is the main purpose of adding custom response headers in a Spring Boot application?

easy

A. To send extra information from the server to the client along with the response

B. To change the HTTP method of the request

C. To modify the request body before processing

D. To encrypt the response data automatically

Solution

1. Step 1: Understand what response headers do

   Response headers carry metadata or extra info about the response from server to client.

2. Step 2: Identify the purpose of custom headers

   Custom headers add extra info beyond standard headers, helping clients handle responses better.

3. Final Answer:

   To send extra information from the server to the client along with the response -> Option A

4. Quick Check:

   Custom headers = extra info sent [OK]

Hint: Custom headers add info to server replies, not change requests [OK]

Common Mistakes:

• Confusing headers with request body changes
• Thinking headers change HTTP methods
• Assuming headers encrypt data automatically

2. Which of the following is the correct way to add a custom header named X-Custom-Header with value 12345 using ResponseEntity in Spring Boot?

easy

A. return ResponseEntity.header("X-Custom-Header", "12345").body(data).ok();

B. return ResponseEntity.body(data).header("X-Custom-Header", "12345");

C. return ResponseEntity.ok().header("X-Custom-Header", "12345").body(data);

D. return ResponseEntity.setHeader("X-Custom-Header", "12345").body(data);

Solution

1. Step 1: Recall ResponseEntity builder pattern

   ResponseEntity.ok() starts building a 200 OK response, then header() adds headers, then body() sets the body.

2. Step 2: Check method chaining order

   Correct chaining is ResponseEntity.ok().header(...).body(...). Other orders or methods like setHeader() do not exist or cause errors.

3. Final Answer:

   return ResponseEntity.ok().header("X-Custom-Header", "12345").body(data); -> Option C

4. Quick Check:

   Use ok() then header() then body() [OK]

Hint: Start with ok(), then add header(), then body() [OK]

Common Mistakes:

• Calling header() after body()
• Using non-existent setHeader() method
• Wrong method chaining order

3. Given this Spring Boot controller method:

public ResponseEntity<String> getData() {
    return ResponseEntity.ok()
        .header("X-Rate-Limit", "1000")
        .header("X-Request-ID", "abc123")
        .body("Success");
}

What headers will the client receive in the response?

medium

A. No custom headers, only body 'Success'

B. Only X-Rate-Limit: 1000

C. Only X-Request-ID: abc123

D. X-Rate-Limit: 1000 and X-Request-ID: abc123

Solution

1. Step 1: Analyze header() calls in method

   Two header() calls add "X-Rate-Limit" with "1000" and "X-Request-ID" with "abc123".

2. Step 2: Confirm both headers are included in response

   ResponseEntity accumulates headers, so both custom headers are sent with the response.

3. Final Answer:

   X-Rate-Limit: 1000 and X-Request-ID: abc123 -> Option D

4. Quick Check:

   Multiple header() calls add multiple headers [OK]

Hint: Multiple header() calls add all headers to response [OK]

Common Mistakes:

• Assuming only last header() call applies
• Thinking headers overwrite each other
• Ignoring headers and focusing on body only

4. Identify the error in this Spring Boot code snippet that tries to add a custom header:

@GetMapping("/test")
public ResponseEntity<String> test() {
    ResponseEntity<String> response = ResponseEntity.ok();
    response.header("X-Test", "value");
    return response.body("Done");
}

medium

A. header() method does not exist on ResponseEntity

B. ResponseEntity.ok() returns an immutable object; header() does not modify it in place

C. body() cannot be called after header()

D. Missing @ResponseBody annotation

Solution

1. Step 1: Understand ResponseEntity immutability

   ResponseEntity.ok() returns a builder, but here it's assigned to ResponseEntity, which is immutable.

2. Step 2: header() returns a new builder; original is unchanged

   Calling header() on ResponseEntity does nothing; must chain calls on builder before building.

3. Final Answer:

   ResponseEntity.ok() returns an immutable object; header() does not modify it in place -> Option B

4. Quick Check:

   ResponseEntity is immutable; use builder chaining [OK]

Hint: Chain header() on builder, not on ResponseEntity instance [OK]

Common Mistakes:

• Trying to modify ResponseEntity after creation
• Confusing builder with built object
• Missing chaining of header() before body()

5. You want to add a custom header X-User-Status with value active only if a user is logged in, otherwise no header. Which is the best way to implement this in a Spring Boot controller method?

hard

A. Use ResponseEntity builder and conditionally call header() before body() based on login status

B. Always add header() with value "active" regardless of login status

C. Add header() after calling body() method

D. Modify HttpServletResponse directly without ResponseEntity

Solution

1. Step 1: Understand conditional header addition

   ResponseEntity builder allows conditional chaining of header() before body() to add headers only when needed.

2. Step 2: Avoid adding headers after body() or always adding unconditionally

   Adding header after body() is invalid; always adding ignores condition; modifying HttpServletResponse is less clean.

3. Final Answer:

   Use ResponseEntity builder and conditionally call header() before body() based on login status -> Option A

4. Quick Check:

   Conditionally chain header() before body() [OK]

Hint: Add headers conditionally before body() in ResponseEntity builder [OK]

Common Mistakes:

• Adding headers after body() call
• Ignoring login condition and always adding header
• Directly modifying HttpServletResponse instead of ResponseEntity