Custom response headers in Spring Boot - Step-by-Step Execution

Concept Flow - Custom response headers

Client sends HTTP request

↓

Spring Boot Controller receives request

↓

Controller method creates response

↓

Add custom headers to response

↓

Send response with headers back to client

The client sends a request, the Spring Boot controller handles it, adds custom headers to the response, and sends it back.

Execution Sample

Spring Boot

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

@RestController
public class GreetingController {

    @GetMapping("/greet")
    public ResponseEntity<String> greet() {
        return ResponseEntity.ok()
            .header("X-Custom-Header", "HelloHeader")
            .body("Hello World");
    }
}

This code creates a GET endpoint that returns "Hello World" with a custom header named X-Custom-Header.

Execution Table

Step	Action	Evaluation	Result
1	Client sends GET /greet request	Request received by server	Request passed to controller method
2	Controller method starts	Prepare response	ResponseEntity builder created
3	Add header X-Custom-Header with value HelloHeader	Header added to response	Response now has custom header
4	Set response body to 'Hello World'	Body set	Response ready to send
5	Send response back to client	Response sent with status 200, header, and body	Client receives response with custom header
6	Client reads response headers	Finds X-Custom-Header	Header value is 'HelloHeader'

💡 Response sent and client received custom header, process complete

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
ResponseEntity	null	Has header X-Custom-Header: HelloHeader	Has body: 'Hello World'	Ready to send with header and body

Key Moments - 3 Insights

Why do we use ResponseEntity instead of just returning a String?

ResponseEntity lets us add headers and status codes, not just the body. See execution_table step 3 where the header is added.

Can we add multiple custom headers?

Yes, by calling .header() multiple times or using .headers() with a map. Each call adds headers before sending.

What happens if we forget to add the header?

The response will not include the custom header. The client won't see it, as shown by absence of header in execution_table step 6.

Visual Quiz - 3 Questions

Look at the execution_table, what is the response body after step 4?

A "Hello World"

B null

C "X-Custom-Header"

D "Goodbye"

💡 Hint

Check the 'Result' column at step 4 in execution_table

At which step is the custom header added to the response?

A Step 5

B Step 2

C Step 3

D Step 6

💡 Hint

Look for the action mentioning header addition in execution_table

If we remove the .header() call, what changes in variable_tracker?

A ResponseEntity will not be created

B ResponseEntity will have no headers after Step 3

C ResponseEntity body will be empty

D ResponseEntity status will be 404

💡 Hint

Check variable_tracker for ResponseEntity headers after Step 3

Concept Snapshot

Custom response headers in Spring Boot:
- Use ResponseEntity to build response
- Add headers with .header(name, value)
- Set body with .body(content)
- Send response with headers and body
- Client receives headers with response

Full Transcript

In Spring Boot, to add custom response headers, the client sends a request to the server. The controller method handles the request and creates a ResponseEntity object. We add custom headers using the .header() method on ResponseEntity. Then we set the response body with .body(). Finally, the response with headers and body is sent back to the client. The client can read the custom headers from the response. This process allows adding extra information in headers beyond just the response content.

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