Javalin - A simple web framework for Java and Kotlin

The project webpage is javalin.io.

Documentation: javalin.io/documentation

Chatroom: https://gitter.im/javalin-io/general

Contributions are very welcome: CONTRIBUTING.md

Java quickstart

Add dependency (maven)

<dependency>
    <groupId>io.javalin</groupId>
    <artifactId>javalin</artifactId>
    <version>1.7.0</version>
</dependency>

Start programming:

import io.javalin.Javalin;

public class HelloWorld {
    public static void main(String[] args) {
        Javalin app = Javalin.create().start(7000);
        app.get("/", ctx -> ctx.result("Hello World"));
    }
}

Kotlin quickstart

Add dependency (gradle)

compile 'io.javalin:javalin:1.7.0'

Start programming

import io.javalin.Javalin

fun main(args: Array<String>) {
    val app = Javalin.create().start(7000)
    app.get("/") { ctx -> ctx.result("Hello World") }
}

Examples

This section contains a few examples, mostly just extracted from the docs. All examples are in Kotlin, but you can find them in Java in the documentation (it's just syntax changes).

Api structure and server config

val app = Javalin.create().apply {
    enableStandardRequestLogging()
    enableDynamicGzip()
    port(port)
}.start()

app.routes {
    path("users") {
        get(UserController::getAllUserIds)
        post(UserController::createUser)
        path(":user-id") {
            get(UserController::getUser)
            patch(UserController::updateUser)
            delete(UserController::deleteUser)
        }
    }
}

Filters and Mappers

app.before("/some-path/*") { ctx ->  ... } // runs before requests to /some-path/*
app.before { ctx -> ... } // runs before all requests
app.after { ctx -> ... } // runs after all requests
app.exception(Exception.class) { e, ctx -> ... } // runs if uncaught Exception
app.error(404) { ctx -> ... } // runs if status is 404 (after all other handlers)

WebSockets

app.ws("/websocket") { ws ->
    ws.onConnect { session -> println("Connected") }
    ws.onMessage { session, message ->
        println("Received: " + message)
        session.remote.sendString("Echo: " + message)
    }
    ws.onClose { session, statusCode, reason -> println("Closed") }
    ws.onError { session, throwable -> println("Errored") }
}

JSON-mapping

var todos = arrayOf(...)
app.get("/todos") { ctx -> // map array of Todos to json-string
    ctx.json(todos)
}
app.put("/todos") { ctx -> // map request-body (json) to array of Todos
    todos = ctx.bodyAsClass(Array<Todo>::class.java)
    ctx.status(204)
}

File uploads

app.post("/upload") { ctx ->
    ctx.uploadedFiles("files").forEach { (contentType, content, name, extension) ->
        content.copyTo(File("upload/" + name))
    }
}

Special thanks

• Blake Mizerany, for creating Sinatra
• Per Wendel, for creating Spark
• Christian Rasmussen, for being a great guy
• Per Kristian Kummermo, also for being a great guy