Demystifying Tomcat: Build a Miniature Web Server in 7 Steps

Tomcat, the widely used Java web server and servlet container, handles incoming HTTP requests by first providing a socket service, then dispatching URLs to the appropriate web applications, and finally wrapping the request and response objects for servlet processing.

1. Provide Socket Service

Tomcat starts by opening a socket that supports the HTTP protocol, which can be based on BIO, NIO, or AIO.

2. Request Dispatch

Tomcat can serve multiple web applications and distributes incoming URLs to the correct application.

3. Encapsulate Request/Response

The container creates request and response objects, so developers do not need to handle low‑level streams directly.

4. Servlet Request Handling Base Class

Tomcat provides the standard Servlet API with methods such as doGet, doPost, and service.

5. Servlet Implementation Classes

Concrete servlet classes extend the base class to implement business logic.

6. Servlet Configuration

Mappings between URLs and servlet classes are defined in web.xml using <servlet> and <servlet-mapping> elements.

7. Startup Class

The main class launches Tomcat, initializing the server and loading the configured servlets.

Testing

After implementing the seven steps, run the application to see Tomcat correctly route URLs, parse HTTP requests, and invoke the appropriate servlet methods.

By building this simplified Tomcat yourself, you gain a deeper understanding of how Java web applications are served.