Demystifying Tomcat: How It Handles Requests in 7 Simple Steps

Tomcat is a widely used Java web server and servlet container. The article breaks down its request‑handling workflow and demonstrates how to build a minimal Tomcat‑like server in seven clear steps, each accompanied by illustrative screenshots.

1. Provide Socket Service

Tomcat starts by opening a socket that listens for HTTP traffic; the socket layer handles low‑level network communication.

2. Dispatch Requests

Because a single Tomcat instance can serve multiple web applications, it parses the incoming URL and forwards the request to the appropriate application context.

3. Wrap Request/Response

Tomcat creates HttpServletRequest and HttpServletResponse objects, encapsulating the raw HTTP data so that developers can work with higher‑level APIs.

4. Servlet Base Class

The container provides an abstract base class that defines the standard doGet, doPost, and service methods required by the Servlet specification.

5. Servlet Implementation

Concrete servlet classes extend the base class and implement the business logic for handling specific URLs.

6. Servlet Configuration

In web.xml, <servlet> and <servlet-mapping> entries bind URLs to the corresponding servlet classes.

7. Startup Class

The main class launches the embedded Tomcat instance, loads the configuration, and starts listening for requests.

Testing

Running the assembled project shows the full request flow: URL parsing, HTTP header extraction, request/response wrapping, servlet instantiation via reflection, and response generation.

By implementing these seven steps yourself, you gain a concrete understanding of Tomcat’s inner workings and move beyond treating it as a black box.