What it is
Jetty is a lightweight, high-performance Java HTTP server and servlet container. It provides an embedded web server, making it easy to integrate into Java applications for serving web content, REST APIs, or acting as a backend server.
Jetty allows you to create embedded HTTP servers, deploy servlets, handle REST APIs, and manage asynchronous requests. It is suitable for both standalone applications and integration with frameworks like Spring or Jersey.
Installation
Add dependency in pom.xml:
<dependency>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-server</artifactId>
<version>11.0.20</version>
</dependency>
<dependency>
<groupId>org.eclipse.jetty</groupId>
<artifactId>jetty-servlet</artifactId>
<version>11.0.20</version>
</dependency>Getting started
The smallest useful thing you can do with it, and what each part means.
import org.eclipse.jetty.server.Server;
Server server = new Server(8080);
server.start();
server.join();import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
context.setContextPath("/");
server.setHandler(context);
context.addServlet(new ServletHolder(new HttpServlet() {
protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
resp.getWriter().println("Hello from Jetty!");
}
}), "/hello");Advanced usage
Where the library earns its place over a simpler alternative.
context.addServlet(new ServletHolder(new HttpServlet() {
protected void doGet(HttpServletRequest req, HttpServletResponse resp) {
AsyncContext async = req.startAsync();
async.start(() -> {
try {
Thread.sleep(1000);
resp.getWriter().println("Async response");
async.complete();
} catch(Exception e) { e.printStackTrace(); }
});
}
}), "/async");import org.glassfish.jersey.server.ResourceConfig;
import org.glassfish.jersey.servlet.ServletContainer;
ResourceConfig config = new ResourceConfig().packages("com.example.resources");
ServletHolder jerseyServlet = new ServletHolder(new ServletContainer(config));
context.addServlet(jerseyServlet, "/api/*");import org.eclipse.jetty.util.ssl.SslContextFactory;
SslContextFactory.Server sslContextFactory = new SslContextFactory.Server();
sslContextFactory.setKeyStorePath("keystore.jks");
sslContextFactory.setKeyStorePassword("password");
ServerConnector sslConnector = new ServerConnector(server, sslContextFactory);
sslConnector.setPort(8443);
server.addConnector(sslConnector);Errors and fixes
The failures you are most likely to hit, and what actually resolves them.
- BindException: Address already in use
- Ensure the configured port is free or change to another port before starting the server.
- ServletException
- Occurs when servlet initialization or processing fails. Check servlet code and mappings.
Best practices
- Use embedded Jetty for microservices and standalone applications for better control.
- Handle exceptions within servlets to avoid server crashes.
- Use thread pools and async requests to handle high concurrency.
- Keep server configuration externalized for flexibility in different environments.
- Combine with frameworks like Spring Boot for easier configuration and dependency injection.
Background
Why it exists, and what it was reacting to.
Jetty was created to offer a flexible and embeddable Java web server for developers. Unlike traditional servlet containers, Jetty can be embedded directly into applications, giving developers control over server lifecycle, configuration, and deployment. It is widely used in microservices, frameworks, and standalone Java applications requiring HTTP capabilities.