Describe the flow of HTTPS requests through a Spring Boot application.

When a client sends an HTTPS request to a Spring Boot application, the request first reaches the embedded web server (such as Tomcat, Jetty, or Undertow), where SSL/TLS encryption is handled. After the request is decrypted, it passes through filters, security layers, controllers, services, and repositories before a response is generated. The response is then encrypted again and sent back securely to the client.

Key Points: • HTTPS uses SSL/TLS to secure communication between the client and server. • The embedded server handles encryption and decryption of data. • Requests pass through filters, security components, controllers, services, and repositories. • Spring Security can authenticate and authorize requests before they reach controllers. • Responses are encrypted before being returned to the client.

HTTPS Request Flow

Client | HTTPS Request | SSL/TLS Handshake | Embedded Server (Tomcat/Jetty/Undertow) | Filters | Spring Security (Optional) | DispatcherServlet | Controller | Service Layer | Repository Layer | Database | Response Generated | SSL/TLS Encryption | Client Receives Response

Step 1: SSL/TLS Handshake

Before any data is exchanged, the client and server perform an SSL/TLS handshake.

During this process:

• Server presents its SSL certificate. • Client verifies the certificate. • Encryption keys are established. • Secure communication channel is created.

This ensures:

• Confidentiality • Integrity • Authentication

Step 2: Embedded Server Receives Request

The HTTPS request reaches the embedded server.

Examples:

• Tomcat • Jetty • Undertow

The server:

• Decrypts incoming data. • Converts it into an HTTP request object. • Forwards it to Spring Boot.

Step 3: Filters Execute

Spring filters intercept the request.

Common filters:

• Logging filters • CORS filters • Authentication filters • Custom request filters

Filters can:

• Modify requests • Validate requests • Log request information

Step 4: Spring Security Processing

If Spring Security is configured:

Request | Authentication | Authorization | Allowed? / \ Yes No | | Continue 401/403

Spring Security verifies:

• User identity • Roles • Permissions

Unauthorized requests are rejected immediately.

Step 5: DispatcherServlet Processing

DispatcherServlet acts as the front controller of Spring MVC.

Responsibilities:

• Receives requests. • Finds matching controller methods. • Delegates processing.

Example:

GET /employees/101

DispatcherServlet maps the request to the appropriate controller.

Step 6: Controller Layer

Code Example:

@RestController
@RequestMapping("/employees")
public class EmployeeController {

    @GetMapping("/{id}")
    public Employee getEmployee(
            @PathVariable Long id) {

return employeeService

                .getEmployee(id);
    }
}

The controller receives the request and delegates business logic to the service layer.

Step 7: Service Layer

The service layer contains business logic.

Code Example:

@Service
public class EmployeeService {

    public Employee getEmployee(
            Long id) {

return repository .findById(id)

                .orElse(null);
    }
}

Responsibilities:

• Business rules • Validation • Transaction management

Step 8: Repository Layer

Repositories interact with the database.

Code Example:

@Repository
public interface EmployeeRepository

extends JpaRepository<

                Employee,
                Long> {
}

The repository executes database operations and returns results.

Step 9: Response Creation

The service returns data to the controller.

Controller returns:

Employee Object

Spring automatically converts it into JSON.

Example Response:

{ "id": 101, "name": "John" }

Step 10: Response Encryption

Before sending the response:

• Embedded server encrypts data using SSL/TLS. • Secure response is transmitted back to the client.

This prevents data interception during transmission.

Example: Suppose a client accesses:

https://api.company.com/employees/101

Flow:

1. HTTPS connection established. 2. SSL/TLS handshake completed. 3. Request reaches Tomcat. 4. Security filters validate user. 5. DispatcherServlet finds controller. 6. Controller calls service. 7. Service retrieves data from database. 8. JSON response created. 9. Response encrypted. 10. Client receives secure response.

Benefits of HTTPS in Spring Boot

• Secure communication • Data encryption • Protection against eavesdropping • Authentication using certificates • Data integrity during transmission

Real-World Example

In a banking application:

Client → HTTPS Request | SSL/TLS Encryption | Spring Security Authentication | Account Controller | Transaction Service | Database | Encrypted Response

Sensitive information such as account balances and transactions remains protected throughout the entire request-response lifecycle.

Interview Tip: A concise interview answer is:

"In a Spring Boot application, an HTTPS request first reaches the embedded server, where SSL/TLS decrypts the incoming data. The request then passes through filters, Spring Security, DispatcherServlet, controllers, services, and repositories. After processing, Spring generates a response, which is encrypted again by SSL/TLS before being sent back securely to the client."