Javalin - A simple web framework for Java and Kotlin
Javalin is a very lightweight web framework for Kotlin and Java which supports WebSockets, HTTP2 and async requests. Javalin’s main goals are simplicity, a great developer experience, and first class interoperability between Kotlin and Java.
Javalin is more of a library than a framework. Some key points:
- You don't need to extend anything
- There are no @Annotations
- There is no reflection
- There is no other magic; just code.
General information:
-
❤️ Sponsor Javalin - The project webpage is javalin.io (repo for webpage is at github.com/javalin/javalin.github.io).
- Documentation: javalin.io/documentation
- Chat on Discord: https://discord.gg/sgak4e5NKv
- Chat on Gitter: https://gitter.im/javalin-io/general
- Contributions are very welcome: CONTRIBUTING.md
- License summary: https://tldrlegal.com/license/apache-license-2.0-(apache-2.0)
- Interesting issues: /tipsy/javalin/issues?q=label:INFO
Quickstart
Add dependency
Maven
<dependency>
<groupId>io.javalingroupId>
<artifactId>javalinartifactId>
<version>4.1.1version>
dependency>
Gradle
implementation "io.javalin:javalin:4.1.1"
Start programming (Java)
ctx.result("Hello World")); } }">
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")); } }
Start programming (Kotlin)
ctx.result("Hello World") } }">
import io.javalin.Javalin fun main() { 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 { config ->
config.defaultContentType = "application/json"
config.autogenerateEtags = true
config.addStaticFiles("/public")
config.asyncRequestTimeout = 10_000L
config.dynamicGzip = true
config.enforceSsl = true
}.routes {
path("users") {
get(UserController::getAll)
post(UserController::create)
path(":user-id") {
get(UserController::getOne)
patch(UserController::update)
delete(UserController::delete)
}
ws("events", userController::webSocketEvents)
}
}.start(port)
WebSockets
ws.onConnect { ctx -> println("Connected") } ws.onMessage { ctx -> val user = ctx.message
(); // convert from json string to object ctx.send(user); // convert to json string and send back } ws.onClose { ctx -> println("Closed") } ws.onError { ctx -> println("Errored") } }">
app.ws("/websocket/:path") { ws -> ws.onConnect { ctx -> println("Connected") } ws.onMessage { ctx -> val user = ctx.message<User>(); // convert from json string to object ctx.send(user); // convert to json string and send back } ws.onClose { ctx -> println("Closed") } ws.onError { ctx -> println("Errored") } }
Filters and Mappers
... } // 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) app.wsBefore("/some-path/*") { ws -> ... } // runs before ws events on /some-path/* app.wsBefore { ws -> ... } // runs before all ws events app.wsAfter { ws -> ... } // runs after all ws events app.wsException(Exception.class) { e, ctx -> ... } // runs if uncaught Exception in ws handler">
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) app.wsBefore("/some-path/*") { ws -> ... } // runs before ws events on /some-path/* app.wsBefore { ws -> ... } // runs before all ws events app.wsAfter { ws -> ... } // runs after all ws events app.wsException(Exception.class) { e, ctx -> ... } // runs if uncaught Exception in ws handler
JSON-mapping
// map array of Todos to json-string ctx.json(todos) } app.put("/todos") { ctx -> // map request-body (json) to array of Todos todos = ctx.body
>() ctx.status(204) }">
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.body<Array<Todo>>() ctx.status(204) }
File uploads
ctx.uploadedFiles("files").forEach { (contentType, content, name, extension) -> FileUtil.streamToFile(content, "upload/$name") } }">
app.post("/upload") { ctx -> ctx.uploadedFiles("files").forEach { (contentType, content, name, extension) -> FileUtil.streamToFile(content, "upload/$name") } }
OpenAPI (Swagger)
Javalin has an OpenAPI (Swagger) plugin. Documentation can be enabled both through a DSL and through annotations, and Javalin can render docs using both SwaggerUI and ReDoc. Read more at https://javalin.io/plugins/openapi.
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
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