What internal processes are done in Apache Tomcat's web server?

Apache Tomcat, being a servlet container and web server for Java-based web applications, performs several internal processes to handle incoming requests, manage the execution of servlets and JSPs, and serve dynamic content. Here are some key internal processes in Apache Tomcat:

1. Request Handling:

   • HTTP Connector: Tomcat uses an HTTP connector to listen for incoming HTTP requests. The connector is responsible for accepting incoming connections on a specified port and passing them to the Tomcat server for processing.

   • Request Processor: Once a request is received, Tomcat's Request Processor takes over. It parses the incoming request, extracts relevant information (such as the requested URL and parameters), and determines which component (servlet or JSP) should handle the request.

2. Servlet Container:

   • Servlet Lifecycle: When a request is mapped to a servlet, Tomcat's servlet container manages the lifecycle of the servlet. This includes the initialization, service, and destruction phases. The servlet container creates instances of servlets, invokes their init() method during initialization, and then calls the service() method to handle each request.

   • Thread Pooling: Tomcat uses a thread pool to manage concurrent requests efficiently. Each incoming request is assigned to a separate thread from the pool, allowing multiple requests to be processed simultaneously.

3. JSP Processing:

   • JSP Compilation: JSP files are automatically compiled into Java servlets by Tomcat's JSP compiler during the first request or at application startup. The compiled servlets are then executed to generate dynamic content.

   • Session Management: Tomcat manages user sessions, allowing web applications to store and retrieve user-specific information. This is crucial for maintaining stateful interactions between the client and the server.

4. Connector and Coyote Adapter:

   • Coyote Connector: This component handles the communication between the web server and Tomcat. It translates incoming requests from the web server (e.g., Apache HTTP Server) to a format that Tomcat can understand and process.

   • Coyote Adapter: In some configurations, an adapter may be used to connect Tomcat to an external web server. For example, the Apache Tomcat Connector (mod_jk) allows integration with the Apache HTTP Server.

5. Session Tracking and Management:

   • Session Manager: Tomcat's session manager is responsible for tracking user sessions. It handles the creation, tracking, and expiration of sessions, allowing web applications to maintain state across multiple requests from the same user.

6. Security Handling:

   • Security Realm: Tomcat supports various security realms for authentication and authorization. Realms define how Tomcat verifies user identities and grants access to protected resources.

   • SSL/TLS Handling: Tomcat can be configured to support secure communication using SSL/TLS protocols. This is important for encrypting data transmitted between the client and the server.

7. Context and Application Management:

   • Context Container: Tomcat manages multiple web applications within a single server instance. Each web application has its own context, and the context container is responsible for creating, initializing, and managing these contexts.

   • Deployment and Reload: Tomcat supports hot deployment, allowing developers to deploy or update web applications without restarting the entire server. The server can also be configured to monitor changes in application files and automatically reload the application.

These processes collectively enable Apache Tomcat to handle the dynamic execution of Java-based web applications, manage user sessions, and ensure the secure and efficient processing of HTTP requests. Each of these components plays a crucial role in the overall functioning of the web server.