Web application from a function. The soul of modern Java web application.

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Java is getting modern and the web ecosystem needs evolution, too. The idea of Espresso is inspired from Ring (Clojure), Iron (Rust) and WSGI (Python). Espresso defined a protocol between web application/framework and web server. It tries to replace Servlet API, which is heavy, verbose, complex and not friendly for unit-test.

Key concepts of espresso ecosystem:

• App: Espresso function implementation.
• Server: A container to run espresso function.
• Adapter: A adapter layer for existed Java web server to run espresso function.
• Plugin or Middleware: An espresso function wrapper that provides additional features or data to core espresso function.

The core of Espresso is an Java interface Espresso, which has only one method that takes a Request as input, and returns a Response.

With Java's functional interface feature, the implementation can be as short as a lambda.

import io.github.espresso4j.espresso.*;

// ...

var app = (req) -> Response.of(200).body("<h1>It works</h1>");

The web app will always return a page says It works.

Espresso also provides an async variance called Espresso.Async if your application is fully asynchronous:

import io.github.espresso4j.espresso.*;

// ...

var app = (req, sender, raiser) ->
        sender.accept(Response.of(200).body("<h1>It works</h1>"));

• Jettino An espresso adapter for Jetty
• Latte url router for Espresso
• Sugar parameter extractor

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