Spring Fu

Spring Fu is an incubator for new Spring features about Kotlin and functional bean registration. Its main feature is an alternative way of configuring Spring Boot applications with Kotlin DSL and lambdas instead of annotations: Kofu (for Kotlin and functional) configuration. Other features like Coroutines or GraalVM support are also included.

A Java variant called Jafu (for Java and functional) is also available (just a POC for now).

It is not intended to be used in production, but rather to incubate and get feedback and contributions from the community in order to reach a point where its features can be integrated as part of existing Spring projects like Framework, Boot and Data. The table bellow summarize the status of current features.

Status

Feature	Status	Related issue
Kofu and Jafu configuration DSL	Incubating in Spring Fu	Slightly related: spring-boot#8115 To be created in Spring Boot issue tracker
More efficient Spring Boot startup via functional bean registration	Manually created in Spring Fu Experimented by Dave Syer in spring-init-experiment and spring-boot-micro-apps Could be generated during Spring Boot build in the future	To be created in Spring Boot issue tracker
Coroutines support	Incubating in Spring Fu	SPR-15413 kotlinx.coroutines#254 kotlinx.coroutines#284 To be created in Spring Data issue tracker for MongoDB and SQL support
Data classes support for configuration properties	Expected in Spring Boot 2.2 (to be confirmed)	spring-boot#8762
GraalVM native images support	Initial support done in Spring Framework 5.1 Work in progress on GraalVM side	SPR-16991 spring-boot graal theme
Better Kotlin documentation	Not started yet	SPR-17245
Gradle Kotlin DSL	Pull-request to be contributed	initializr#334
Lite Kotlin reflection support	Incubating in Spring Fu	SPR-17008
Spring classpath filtering via Gradle plugin	Not started yet
Automated (and machine readable) HTTP API documentation	Not started yet	spring-restdocs#213

Getting started

Via start.spring.io

• Create a Spring 2.1.x.RELEASE project on start.spring.io,

• Add the org.springframework.fu:spring-fu-kofu:0.0.3.BUILD-SNAPSHOT dependency

• Add the Reactive Web org.springframework.boot:spring-boot-starter-webflux dependency

• Use latest Kotlin 1.3.x

• Modify the generated *Application.kt file as following:

package com.example

import org.springframework.fu.kofu.application

val app = application {
	// your application here
	server {
		router {
			GET("/") { ok().syncBody("Hello world!") }
		}
	}
}

fun main() = app.run()

Samples

You can also have a look to the sample applications.

Credits

In addition to the whole Spring and Reactor teams, special credits to:

• Juergen Hoeller for his support on Kotlin and the functional bean registration API

• Arjen Poutsma for creating the WebFlux functional API

• Thomas Girard for its spring-webflux-kotlin-dsl experiment that initially demonstrated this approach was possible

• Konrad Kaminski for his awesome spring-kotlin-coroutine project

• Dave Syer for his work on benchmarks, GraalVM support and functional bean registration applied to Boot

• The whole Spring Boot team