Introduction to Apache Tomcat

What is Tomcat?

Apache Tomcat is an open-source servlet container (also called a servlet/JSP engine) and web server. It implements the Jakarta Servlet, JSP, EL and WebSocket specifications. Spring Boot and Struts apps typically run inside Tomcat, embedded or standalone.

Tomcat vs a Full App Server

• Tomcat - lightweight; runs servlets, JSP and WebSockets. Perfect for web applications.
• GlassFish / JBoss / WildFly - full Jakarta EE platforms adding EJB, JMS, JPA container etc.
• Spring Boot - usually embeds Tomcat directly in a runnable jar instead of a WAR on a server.

How a Request Flows

Browser -> Connector -> Engine -> Host -> Context (your webapp)
    -> Servlet/Filters -> Database -> Response back

Key Concepts

• Connector - listens on a port (8080 HTTP, 8443 HTTPS) and converts bytes into requests.
• Engine - the central request-processing object.
• Host - a virtual host; usually matching a domain name.
• Context - one deployed web application.

Key Points

• Tomcat is ideal for servlet/JSP and Spring web apps without full Jakarta EE.
• Everything is configured in XML under conf/ (server.xml, web.xml, context.xml).
• Understand Engine/Host/Context - they map to how you deploy apps.