Custom response headers in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Spring Boot controller method?

Consider this Spring Boot controller method that adds a custom header to the response:

  @GetMapping("/greet")
  public ResponseEntity greet() {
      return ResponseEntity.ok()
          .header("X-Custom-Header", "HelloWorld")
          .body("Greetings!");
  }

What will the HTTP response include?

Spring Boot

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

A HTTP 200 with body 'Greetings!' but no custom headers

B HTTP 200 with body 'Greetings!' and header 'X-Custom-Header: HelloWorld'

C HTTP 404 error because header method is invalid

D HTTP 500 error due to missing @ResponseBody annotation

💡 Hint

Think about how ResponseEntity builds the response including headers.

The ResponseEntity builder allows adding headers with the header() method. This code returns status 200 with the body and the custom header included.

📝 Syntax

intermediate

Which option correctly adds multiple custom headers in Spring Boot?

You want to add two custom headers X-First and X-Second with values One and Two respectively. Which code snippet does this correctly?

A return ResponseEntity.ok().header("X-First", "One", "X-Second", "Two").body("Done");

B return ResponseEntity.ok().headers(Map.of("X-First", "One", "X-Second", "Two")).body("Done");

C return ResponseEntity.ok().header("X-First", "One").header("X-Second", "Two").body("Done");

D return ResponseEntity.ok().header(Map.of("X-First", "One", "X-Second", "Two")).body("Done");

💡 Hint

Check the method signatures for adding headers in ResponseEntity.

The header() method adds one header at a time. To add multiple headers, chain multiple header() calls. The headers() method expects an HttpHeaders object, not a Map.

🔧 Debug

advanced

Why does this code fail to add a custom header?

Examine this Spring Boot controller method:

  @GetMapping("/test")
  public String test(HttpServletResponse response) {
      response.setHeader("X-Test", "Value");
      return "Hello";
  }

But the response does not include the X-Test header. Why?

Spring Boot

  @GetMapping("/test")
  public String test(HttpServletResponse response) {
      response.setHeader("X-Test", "Value");
      return "Hello";
  }

A Because the header name 'X-Test' is reserved and ignored

B Because HttpServletResponse cannot set headers in Spring Boot

C Because setHeader method requires flushing the response manually

D Because returning String causes Spring to treat it as a view name, not response body

💡 Hint

Think about what returning a String means in Spring MVC.

Returning a String without @ResponseBody or ResponseEntity makes Spring treat it as a view name. The response headers set on HttpServletResponse are ignored because the view rendering happens later.

🧠 Conceptual

advanced

What is the best way to add a custom header to all responses in Spring Boot?

You want to add a header X-App-Version with value 1.0 to every HTTP response from your Spring Boot app. Which approach is correct?

A Create a Filter that adds the header to HttpServletResponse before chain.doFilter()

B Add the header in every controller method manually

C Use @ControllerAdvice with @ModelAttribute to add the header

D Set the header in application.properties with server.custom.header

💡 Hint

Think about a centralized way to modify all responses.

A Filter can intercept all requests and add headers to the response before passing control. This is the standard way to add headers globally. Adding in every controller is repetitive. @ModelAttribute is for model data, not headers. application.properties does not support custom headers directly.

❓ state_output

expert

What headers are present after this Spring Boot controller runs?

Given this controller method:

  @GetMapping("/multi")
  public ResponseEntity multiHeaders() {
      HttpHeaders headers = new HttpHeaders();
      headers.add("X-First", "One");
      headers.add("X-Second", "Two");
      headers.set("X-First", "Uno");
      return new ResponseEntity<>("Done", headers, HttpStatus.OK);
  }

Which headers will the HTTP response include?

Spring Boot

  @GetMapping("/multi")
  public ResponseEntity<String> multiHeaders() {
      HttpHeaders headers = new HttpHeaders();
      headers.add("X-First", "One");
      headers.add("X-Second", "Two");
      headers.set("X-First", "Uno");
      return new ResponseEntity<>("Done", headers, HttpStatus.OK);
  }

A X-First: Uno; X-Second: Two

B X-First: One; X-Second: Two

C X-First: One, Uno; X-Second: Two

D No headers included

💡 Hint

Check the difference between add() and set() methods on HttpHeaders.

The add() method appends a header value, while set() replaces all existing values for that header. So set("X-First", "Uno") replaces the earlier 'One' value.