How to Test Response Headers of API by Rest Assured

 

What are Response Headers?

When a client (like a browser or an API testing tool) makes an HTTP request to a server, the server responds with:

• Status Line → (status code like 200 OK, 404 Not Found, etc.)
• Response Headers → Metadata about the response.
• Response Body → The actual content/data returned (like JSON, HTML, XML).

Response Headers are key–value pairs that provide additional information about the response.

Examples:

• Content-Type → format of response body (application/json, text/html, etc.).
• Content-Length → size of the response body in bytes.
• Server → server type (e.g., Apache, Nginx).
• Cache-Control → caching policies.
• Set-Cookie → cookies sent by the server.
• Date → time when the response was generated.

Why Test Response Headers in API Testing?

Testing headers is important because they:

• Ensure correct data format → e.g., Content-Type must be application/json if API promises JSON.

• Security checks → headers like Strict-Transport-Security, X-Content-Type-Options, etc. help secure APIs.

• Performance checks → Cache-Control, Expires help manage caching.

• Compliance checks → some APIs must include custom headers for authorization, tracking, etc.

• Troubleshooting → headers help identify server/software versions or errors.

Steps to test response headers using Rest Assured:

• Set Base URI using RestAssured.baseURI
• Send GET Request using given().get(endpoint)
• Extract Headers from the response
• Verify Specific Headers using assertions
  
  

Maven Dependency for Rest Assured

<dependencies>
    <dependency>
        <groupId>io.rest-assured</groupId>
        <artifactId>rest-assured</artifactId>
        <version>5.3.2</version>
        <scope>test</scope>
    </dependency>
</dependencies>

Java Code: Get and Test Response Headers

import io.restassured.RestAssured;
import io.restassured.response.Response;
import io.restassured.http.Headers;
import io.restassured.http.Header;

public class GetResponseHeaders {

    public static void main(String[] args) {

        // Step 1: Set Base URI
        RestAssured.baseURI = "https://reqres.in/api";

        // Step 2: Send GET request
        Response response = RestAssured
                .given()
                .get("/users?page=2");

        // Step 3: Print all headers
        Headers allHeaders = response.getHeaders();
        System.out.println("===== All Response Headers =====");
        for (Header header : allHeaders) {
            System.out.println(header.getName() + ": " + header.getValue());
        }

        // Step 4: Get a specific header
        String contentType = response.getHeader("Content-Type");
        String server = response.getHeader("Server");

        System.out.println("\nContent-Type: " + contentType);
        System.out.println("Server: " + server);

        // Step 5: Validate headers using assertions
        if (!"application/json; charset=utf-8".equals(contentType)) {
            throw new AssertionError("Expected Content-Type not found!");
        }

        if (!"cloudflare".equalsIgnoreCase(server)) {
            throw new AssertionError("Expected Server header value not found!");
        }

        System.out.println("\n Header validations passed successfully!");
    }
}

Code explanation:

1. Set Base URI

2. Send GET Request

3. Print all headers on console

4. Get a specific header

5. Validate headers using assertions

Output:

===== All Response Headers =====
Date: Mon, 28 Jul 2025 14:00:00 GMT
Content-Type: application/json; charset=utf-8
Transfer-Encoding: chunked
Connection: keep-alive
Server: cloudflare
...

Content-Type: application/json; charset=utf-8
Server: cloudflare

Header validations passed successfully!

Useful Methods in Rest Assured

• response.getHeaders() – Gets all headers
• response.getHeader("Header-Name") – Gets a specific header
• response.header("Header-Name") – Alias for getHeader