How Tomcat Works

Overview

This chapter explains how you can develop your own servlet container by presenting two applications. The first application has been designed to be as simple as possible to make it easy for you to understand how a servlet container works. It then evolves into the second servlet container, which is slightly more complex.

Note: Every servlet container application in each chapter gradually evolves from the application in the previous chapter, until a fully-functional Tomcat servlet container is built in Chapter 17.

Both servlet containers can process simple servlets as well as static resources. You can use PrimitiveServlet to test this container. PrimitiveServlet is given in Listing 2.1 and its class file can be found in the webroot directory. More complex servlets are beyond the capabilities of these containers, but you will learn how to build more sophisticated servlet containers in the next chapters.

Listing 2.1: PrimitiveServlet.java

import javax.servlet.*;
import java.io.IOException;
import java.io.PrintWriter;
public class PrimitiveServlet implements Servlet {
    public void init(ServletConfig config) throws ServletException {
        System.out.println("init");
    }
    public void service(ServletRequest request,ServletResponse response) throws ServletException, IOException {
        System.out.println("from service");
        PrintWriter out = response.getWriter();
        out.println("Hello. Roses are red.");
        out.print("Violets are blue.");
    }
    public void destroy() {
        System.out.println("destroy");
    }
    public String getServletInfo() {
        return null;
    }
    public ServletConfig getServletConfig() {
        return null;
    }
}