Custom response headers in Spring Boot

Introduction

Custom response headers let you add extra information to what your server sends back. This helps clients understand or handle the response better.

You want to tell the client about the type of content or version of your API.

You need to send security info like CORS policies or tokens.

You want to pass metadata like request IDs or timing info for debugging.

You want to control caching behavior for the client.

You want to add custom flags or messages for the client to read.

Syntax

Spring Boot

return ResponseEntity.ok()
    .header("Header-Name", "Header-Value")
    .body(responseBody);

Use ResponseEntity to build responses with custom headers easily.

You can add multiple headers by chaining .header() calls.

Examples

Adds a custom header named X-Custom-Header with value MyValue to the response.

Spring Boot

return ResponseEntity.ok()
    .header("X-Custom-Header", "MyValue")
    .body("Hello World");

Creates headers separately and adds them to the response.

Spring Boot

HttpHeaders headers = new HttpHeaders();
headers.add("X-Rate-Limit", "1000");
return ResponseEntity.ok()
    .headers(headers)
    .body("Data");

Sets a cache control header to tell clients not to cache the response.

Spring Boot

@GetMapping("/example")
public ResponseEntity<String> example() {
    return ResponseEntity.ok()
        .header("Cache-Control", "no-cache")
        .body("Cached data");
}

Sample Program

This Spring Boot controller has one endpoint /greet. It sends back a greeting message with a custom header X-Greeting set to HelloUser.

Spring Boot

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

@RestController
public class HeaderController {

    @GetMapping("/greet")
    public ResponseEntity<String> greet() {
        return ResponseEntity.ok()
            .header("X-Greeting", "HelloUser")
            .body("Welcome to our service!");
    }
}

Important Notes

Custom headers should use names that start with 'X-' or be clearly unique to avoid conflicts.

Headers are case-insensitive but it's good to keep consistent casing for readability.

Use ResponseEntity to control headers, status, and body together cleanly.

Summary

Custom response headers add extra info to server replies.

Use ResponseEntity in Spring Boot to add headers easily.

Headers help clients handle responses better and add metadata.

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