JExpress.java, a light and slow express.js clone written in Java 17 (in one file). It uses virtual threads if run with Java 21 (or Java 19/20 with --enable-preview).

There is also JExpress8.java, a version backward compatible with Java 8.

• JExpress: express(), get(path, callback), post(path, callback), put(path, callback), delete(path, callback), use(path, handler), listen(port) and staticFiles(root).
• Request: bodyArray(), bodyObject(), bodyText(), get(header), method(), param(name) and path().
• Response: status(status), type(type, charset), set(field, value), append(field, value), json(object), send(body) and sendFile(path).

The full javadoc

public static void main(String[] args) {
  var app = express();
  app.use(staticFiles(Path.of("public")));

  app.get("/hello/:id", (req, res) -> {
    var id = req.param("id");
    record Hello(String id) {}
    res.json(new Hello(id));
  });
  
  app.get("/LICENSE", (req, res) -> {
    res.sendFile(Path.of("LICENSE"));
  });

  app.listen(3000);
}

• Run the application with

  cd src/main/java
  java JExpress.java
  

• Test the application with Maven

  mvn clean package