Jonas Notes

Tomcat

2 min read

Overview

  • Tomcat is the default embedded web server in Spring Boot.
  • It listens on a port (default 8080), parses HTTP requests, and routes them to Spring.
  • No need to install it separately — it’s bundled inside your app.

⚖️ Tomcat vs Nginx

  • Tomcat → Application server (executes Java code, Servlets, Spring controllers).
  • Nginx → Web server / reverse proxy (serves static files, load balances, SSL termination).
  • Production setup: Nginx in front, Tomcat behind.

🔄 Tomcat Equivalent in Django

  • Django doesn’t use Tomcat.
  • Instead, it runs on WSGI servers:
    • Sync: Gunicorn, uWSGI
    • Async: Uvicorn, Daphne
  • These are the Python equivalents of Tomcat → execute Django code and handle HTTP requests.

🛠 Spring Boot Abstractions

Spring Boot hides a lot of boilerplate:

  1. Embedded servlet container (Tomcat / Jetty / Undertow).
  2. Auto-configured beans and dependency injection.
  3. Fat JAR packaging (no manual WAR deploy).
  4. Database configs (DataSource, JPA, transactions).
  5. Spring MVC setup (DispatcherServlet, JSON converters).
  6. Security defaults.
  7. Logging (Logback pre-configured).
  8. Actuator (health, metrics).
  9. Config management (application.yml, profiles).
  10. Starter dependencies (one line pulls in all you need).

🏷 Category

  • Tomcat & WSGI servers = Application servers (Web Application Servers).
  • Different from Web servers like Nginx/Apache.

⚙️ How Tomcat Works Internally

  • Runs inside the JVM.
  • Handles network I/O: opens sockets, parses HTTP from TCP streams.
  • Creates HttpServletRequest & HttpServletResponse objects.
  • Hands requests to Spring DispatcherServlet, which calls controllers.
  • Gets response back, serializes it to HTTP, and writes it out.
  • OS kernel manages low-level TCP/IP packet assembly; Tomcat deals only with HTTP streams.

✅ In Short

  • Tomcat = Embedded application server in Spring Boot.
  • WSGI servers (Gunicorn/uWSGI/Uvicorn) = Django’s equivalent.
  • Nginx = Not the same; it’s a reverse proxy / web server.
  • Spring Boot abstracts a ton (server, beans, config, security, logging, monitoring).
  • Tomcat runs in JVM, parses HTTP, delegates to Spring, and returns responses.

📊 (Optional Diagram Idea)

Nginx (reverse proxy, SSL, static files)  
⬇️  
Tomcat (Spring Boot embedded server, Java execution)  
⬇️  
Spring DispatcherServlet → Controllers → Response

Nginx (reverse proxy, SSL, static files)  
⬇️  
Gunicorn / uWSGI / Uvicorn (Django WSGI server, Python execution)  
⬇️  
Django app → Views → Response

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