HTTP Headers

• Used to share metadata between client and server.
• Sent as part of HTTP request and response.
• Represented as key–value pairs.
• Can include custom headers (e.g., X-Auth-Token).

Types of Headers

Type	Description
General Headers	Apply to both requests and responses.
Request Headers	Sent by client to provide information about the request.
Response Headers	Sent by server to provide information about the response.
Entity Headers	Describe the body content (if present).

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Common Request Headers

Header	Description	Example
Host	Domain name of the server.	Host: example.com
User-Agent	Info about client software.	User-Agent: Chrome/141.0
Accept	Expected response format.	Accept: application/json
Authorization	Credentials for authentication.	Authorization: Bearer <token>
Cookie	Sends stored cookies.	Cookie: sessionId=abc123

Common Response Headers

Header	Description	Example
Content-Type	Media type of the response body.	Content-Type: application/json
Content-Length	Size of response body in bytes.	Content-Length: 348
Server	Server software info.	Server: Apache/2.4.56
Set-Cookie	Sends cookies to client.	Set-Cookie: sessionId=abc123
Location	Used in redirects.	Location: /login
Cache-Control	Defines caching rules.	Cache-Control: no-cache

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Request Headers

Example

GET /users HTTP/1.1
Host: api.example.com
Accept: application/json
Authorization: Bearer xyz123

Response Headers

Example

HTTP/1.1 200 OK
Content-Type: application/json
Cache-Control: no-cache

1. Read Header Value from Request

To read header values from an incoming request, two common ways:

• Using RequestHeader
  • Reads a specific header directly.
  • Use@RequestHeader Map<String, String> to get all headers.
• Using HttpServletRequest
  • request.getHeader("name") : read a single header.
  • request.getHeaderNames() : get all header names.

@RequestHeader – Required and Default Value Behavior

@RequestHeader(
    name="Security-token" ,
    required=false,
    defaultValue = "token"
    ) String token

Client Sends Header?	required Value	defaultValue Provided?	Result	Description
Yes	—	—	Value from client	The header value sent by client is used.
No	required = true	—	400 Bad Request	Header is mandatory, but missing.
No	required = false	—	Value = null	Header is optional; value will be null.
No	required = false	Yes	Value = token	Default value used instead of null.

2. Add Header to Response

Using ResponseEntity

@GetMapping("/custom-header")
public ResponseEntity<String> sendHeader() {
    return ResponseEntity
            .ok()
            .header("X-App-Name", "SpringBootDemo")
            .body("Header added successfully!");
}

Here,

• header("name", "value") → Adds custom header to response.
• add multiple headers: .headers(HttpHeaders headers)

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