Custom response headers in Spring Boot - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a custom response header in Spring Boot?

A custom response header is an additional piece of information added to the HTTP response by the server. In Spring Boot, you can add these headers to provide extra data to the client beyond the standard headers.

beginner

How do you add a custom response header using Spring Boot's ResponseEntity?

You can add custom headers by creating an HttpHeaders object, adding your headers to it, and then passing it to ResponseEntity. For example:
HttpHeaders headers = new HttpHeaders();
headers.add("X-Custom-Header", "value");
return new ResponseEntity<>(body, headers, HttpStatus.OK);

intermediate

What is the purpose of the @ResponseHeader annotation in Spring Boot?

Spring Boot does not have a @ResponseHeader annotation. Instead, you add custom headers using HttpServletResponse, ResponseEntity, or WebFilter. This is important to know to avoid confusion.

beginner

How can you add a custom header using HttpServletResponse in a Spring Boot controller?

You can inject HttpServletResponse into your controller method and call response.addHeader("X-Custom-Header", "value") before returning the response body.

beginner

Why might you want to add custom response headers in a web application?

Custom headers can provide extra information like security tokens, version info, or debugging data. They help clients understand or handle the response better without changing the response body.

Which class in Spring Boot is commonly used to add custom response headers?

A HttpServletRequest

B HttpHeaders

C RequestBody

D PathVariable

HttpHeaders is used to set custom headers in the response.

How do you add a custom header using HttpServletResponse?

A response.addHeader("X-Name", "value")

B response.setBody("X-Name", "value")

C response.getHeader("X-Name")

D response.removeHeader("X-Name")

The addHeader method adds a new header to the response.

What is the correct way to return a response with custom headers using ResponseEntity?

A new ResponseEntity<>(headers, body, status)

B new ResponseEntity<>(status, headers, body)

C new ResponseEntity<>(body, headers, status)

D new ResponseEntity<>(body, status, headers)

The constructor takes body, headers, then status in that order.

Which of these is NOT a reason to add custom response headers?

A To change the HTTP method

B To send extra info like tokens

C To provide version info

D To help with debugging

Custom headers do not change the HTTP method.

Can you add multiple custom headers in Spring Boot response?

A Only if you use @ResponseHeader

B No, only one header is allowed

C Only with XML configuration

D Yes, by adding multiple headers to HttpHeaders

You can add as many headers as needed using HttpHeaders.

Explain how to add a custom response header in a Spring Boot controller using ResponseEntity.

Think about how you build the response with headers included.

Describe why custom response headers are useful in web applications.

Consider what extra data headers can carry.

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