Undertow is a flexible, high-performance web server written in Java. It is designed to be embedded within applications, providing a lightweight and scalable HTTP server that can be easily integrated into a variety of Java-based projects.

Pros

• Lightweight and Scalable: Undertow is designed to be highly efficient, with a small footprint and the ability to handle a large number of concurrent connections.
• Flexible and Extensible: Undertow provides a modular architecture that allows developers to easily extend and customize its functionality to meet their specific needs.
• High-Performance: Undertow is built on top of the Netty networking framework, which provides a high-performance, asynchronous I/O implementation.
• Supports Modern Web Technologies: Undertow supports a wide range of web technologies, including HTTP/2, WebSockets, and HTTP/1.1.

Cons

• Limited Documentation: While Undertow has a growing community, the documentation can be sparse in some areas, which may make it challenging for new users to get started.
• Steep Learning Curve: Undertow's flexibility and extensibility can also make it more complex to set up and configure, especially for developers who are new to the project.
• Lack of Widespread Adoption: Compared to other popular Java web servers like Tomcat or Jetty, Undertow has a smaller user base, which may limit the availability of third-party libraries and resources.
• Potential Performance Overhead: While Undertow is designed to be highly performant, the use of its advanced features, such as HTTP/2 or WebSockets, may introduce some performance overhead in certain scenarios.

Code Examples

Here are a few examples of how to use Undertow in your Java projects:

Serving a Simple HTTP Response

Undertow server = Undertow.builder()
    .addHttpListener(8080, "localhost")
    .setHandler(exchange -> {
        exchange.getResponseHeaders().put(Headers.CONTENT_TYPE, "text/plain");
        exchange.getResponseSender().send("Hello, World!");
    })
    .build();

server.start();

This code sets up a simple Undertow server that listens on localhost:8080 and responds with the message "Hello, World!" when a client connects.

Handling WebSocket Connections

Undertow server = Undertow.builder()
    .addHttpListener(8080, "localhost")
    .setHandler(path("websocket").addExactPath("/echo")
        .to(WebSocketProtocolHandlerFactory.builder()
            .addProvider(new EchoWebSocketProtocolProvider())
            .build()))
    .build();

server.start();

This example demonstrates how to set up a WebSocket endpoint that echoes back any messages sent to it.

Serving Static Files

Undertow server = Undertow.builder()
    .addHttpListener(8080, "localhost")
    .setHandler(resource(new ClassPathResourceManager(getClass().getClassLoader(), "static"))
        .setDirectoryListingEnabled(true))
    .build();

server.start();

This code sets up an Undertow server that serves static files from the static directory in the classpath.

Getting Started

To get started with Undertow, you can add the following dependency to your Maven or Gradle project:

<dependency>
    <groupId>io.undertow</groupId>
    <artifactId>undertow-core</artifactId>
    <version>2.3.0.Final</version>
</dependency>

Once you have the dependency set up, you can start building your Undertow-based application. The examples provided earlier should give you a good starting point for common use cases. For more advanced usage and configuration options, refer to the Undertow documentation.