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

Concept Flow - Custom response headers

Client sends HTTP request

↓

Spring Boot Controller receives request

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Controller method creates response

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Add custom headers to response

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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.