Implementing a Simple Tomcat-like Server (MyTomcat): Architecture and Code Walkthrough

Preface

Tomcat, the three‑legged cat I first met in university, still appears in my work; it is a magical server, and today I will abstract it and implement it for you!

Tomcat

Write MyTomcat

Tomcat is a very popular web server and also a container that complies with the Servlet specification. How does Tomcat relate to our web applications?

In practice, we package a web application as a WAR file and deploy it to Tomcat. Inside the application we must specify which class and method handle each URL (whether using raw Servlets or modern Spring MVC).

Because the web application runs inside Tomcat, every request first reaches Tomcat, which then processes the request as follows:

1. Provide Socket Service

Tomcat starts by offering a socket service that speaks the HTTP protocol.

We can further ask: does Tomcat use BIO, NIO, or AIO for its sockets?

2. Dispatch Requests

Tomcat can serve multiple web applications, so it distributes incoming URLs to the appropriate application.

3. Wrap Request and Response

We never manually wrap request/response objects in our web layer; Tomcat does it for us.

Now let’s look at the project screenshot:

Project Structure

MyRequest

Encapsulating the Request Object

Here you can clearly see that we parse the HTTP request line and URL by reading from the input stream.

MyResponse

Encapsulating the Response Object

Output is written according to the HTTP protocol format.

MyServlet

Providing a Servlet

Since Tomcat implements the Servlet specification, it provides the typical doGet/doPost/service methods.

FindGirlServlet and HelloWorldServlet

FindGirlServlet

HelloWorldServlet

These two concrete Servlet implementations are provided only for testing purposes.

ServletMapping and ServletMappingConfig

Servlet configuration

Servlet configuration

You should now feel the flow: in servlet development we declare <servlet> and <servlet-mapping> in web.xml to bind URLs to specific servlets.

MyTomcat

Port

start method

start

dispatch

Here you can see Tomcat’s processing flow: map URLs to Servlets, parse HTTP, wrap request/response objects, and use reflection to instantiate the appropriate Servlet for handling.

Test MyTomcat

running!

Ok, MyTomcat is so ugly, but I like it!

Finally, wish everyone a happy National Day holiday!!!

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