Here’s a detailed explanation of the Java Spring Boot HTTP request lifecycle:
1. Client Request
The lifecycle starts when a client (such as a web browser or a REST client) sends an HTTP request to the Spring Boot application.
2. Web Server
The request reaches the web server (such as Apache Tomcat, which is embedded in Spring Boot applications) that forwards it to the Spring Boot application.
3. Servlet Container
The web server passes the request to the servlet container. In Spring Boot, this is handled by the DispatcherServlet.
4. DispatcherServlet Initialization
Configuration: DispatcherServlet is initialized based on the configuration specified in the application.
Handler Mapping: It uses handler mappings to determine which controller method should handle the request.
5. Middleware Processing (Filters & Interceptors)
Filters: The request first goes through a series of filters (such as authentication filters) before reaching the servlet.
Interceptors: After filters, interceptors can be used to perform operations both before and after the request is handled by a controller.
6. Controller Handler Mapping
DispatcherServlet uses handler mappings to find the appropriate controller and its method to handle the incoming request.
7. Controller Method Execution
Request Handling: The matched controller method is executed. This method contains the business logic to process the request.
Service Layer: The controller method may call services in the service layer to perform business operations.
8. View Resolution
Response Creation: The controller method prepares the response data.
View Resolver: If the controller method returns a view (like a Thymeleaf template), the view resolver will resolve the view to be rendered.
9. Middleware Processing (Response)
Interceptors: After the controller has generated a response, interceptors can modify the response before it is sent back to the client.