Jetty — Lightweight Embeddable Java Web Server

Introduction

Eclipse Jetty is a Java-based web server and servlet container used in production by thousands of organizations. Its embeddable design means you can start a full HTTP server from a main() method with a few lines of code, avoiding the overhead of deploying WAR files to an external container. Jetty also runs as a standalone distribution for traditional deployments.

What Jetty Does

• Serves HTTP/1.1, HTTP/2, and HTTP/3 (QUIC) traffic with a unified handler API
• Implements the Jakarta Servlet, WebSocket, and JSP specifications
• Embeds directly into Java applications as a library dependency
• Provides an asynchronous I/O layer built on Java NIO for high concurrency
• Supports TLS, ALPN, and proxy protocols out of the box

Architecture Overview

Jetty is built around a Connector-Handler pipeline. Connectors accept network connections and negotiate protocols; Handlers process requests. Handlers can be composed into trees — a ContextHandlerCollection routes by path, a ServletHandler dispatches to servlets, and a GzipHandler compresses responses. The underlying transport layer uses an event-driven I/O model with configurable thread pools. This architecture allows Jetty to handle tens of thousands of concurrent connections on modest hardware.

Self-Hosting & Configuration

• Embed via Maven/Gradle: add jetty-server and jetty-servlet dependencies
• Create a Server instance, attach handlers or servlets, and call server.start()
• For standalone use, download the Jetty distribution and deploy WAR files into $JETTY_BASE/webapps
• Configure connectors, thread pools, and TLS in jetty.xml or programmatically
• Enable HTTP/2 by adding the jetty-http2 module and configuring ALPN

Key Features

• Embeddable design — no external container needed, perfect for microservices
• Full HTTP/2 and experimental HTTP/3 support with automatic protocol negotiation
• Low memory footprint compared to full application servers
• Proven at scale — used by Google App Engine, Eclipse IDE, and Jenkins
• Active maintenance under the Eclipse Foundation with frequent releases

Comparison with Similar Tools

• Tomcat — Similar servlet container; Jetty is lighter and more embed-friendly while Tomcat is more widely used standalone
• Undertow — Red Hat's embeddable server; Jetty has broader protocol support including HTTP/3
• Netty — Low-level network framework; Jetty provides servlet-level abstractions on top
• Spring Boot embedded — Uses Tomcat, Jetty, or Undertow under the hood; Jetty is one of the pluggable options
• Nginx/Caddy — Native reverse proxies; Jetty is a Java application server, not a general-purpose proxy

FAQ

Q: Can I use Jetty as a reverse proxy? A: Yes. Jetty includes a ProxyServlet and an AsyncProxyServlet for forwarding requests to upstream services.

Q: How does Jetty compare to Tomcat for Spring Boot? A: Both work as embedded containers in Spring Boot. Jetty tends to use less memory and starts faster; Tomcat has broader community adoption.

Q: Does Jetty support Jakarta EE? A: Jetty 12 supports both javax and jakarta namespaces through its environment abstraction, making migration seamless.

Q: What Java version does Jetty require? A: Jetty 12 requires Java 17 or later. Jetty 11 supports Java 11+.

Sources

• https://github.com/jetty/jetty.project
• https://jetty.org/docs/