Understanding MyTomcat: Building a Custom Tomcat‑like Server with Request/Response Handling

In this tutorial the author, a senior architect, introduces MyTomcat , a handcrafted implementation that mimics the core functions of Apache Tomcat, a popular Java web server and servlet container.

Tomcat and Web Applications

Tomcat serves as both an HTTP socket server and a servlet container. A typical web application is packaged as a WAR file and deployed to Tomcat, where URL patterns are mapped to specific servlet classes (whether using raw Servlets or frameworks like Spring MVC).

Three Core Responsibilities of Tomcat

1. Provide Socket Service – Tomcat starts a socket listener that speaks HTTP (underlying I/O can be BIO, NIO, or AIO).

2. Dispatch Requests – It matches incoming URLs to the appropriate web application and servlet.

3. Encapsulate Request/Response – Tomcat parses the HTTP request and creates HttpServletRequest and HttpServletResponse objects for the servlet to use.

MyRequest – Request Wrapper

The MyRequest class parses the raw input stream, extracts the HTTP method, headers, and URL, and builds a request object that the servlet can consume.

MyResponse – Response Wrapper

The MyResponse class formats the output according to the HTTP protocol and writes it back to the client.

MyServlet and Example Servlets

Two concrete servlets – FindGirlServlet and HelloWorldServlet – demonstrate how a servlet processes a request via doGet , doPost , or service methods.

Servlet Mapping Configuration

In a traditional web.xml the relationship between URLs and servlets is defined with <servlet></servlet> and <servlet-mapping></servlet-mapping> elements.

MyTomcat Startup and Dispatch Flow

The start method opens the listening port, accepts connections, parses the request, creates MyRequest and MyResponse , looks up the servlet mapping, instantiates the target servlet via reflection, and invokes its processing method.

Testing MyTomcat

Screenshot of a test run shows successful handling of HTTP requests and proper response generation.

Overall, the article provides a step‑by‑step walkthrough of building a minimal Tomcat‑like server, illustrating the essential backend concepts of socket handling, request routing, and servlet execution.