= Introduction

Spring Cloud Function is a project with the following high-level goals:

* Promote the implementation of business logic via functions.
* Decouple the development lifecycle of business logic from any specific runtime target so that the same code can run as a web endpoint, a stream processor, or a task.
* Support a uniform programming model across serverless providers, as well as the ability to run standalone (locally or in a PaaS).
* Enable Spring Boot features (auto-configuration, dependency injection, metrics) on serverless providers.

It abstracts away all of the transport details and
infrastructure, allowing the developer to keep all the familiar tools
and processes, and focus firmly on business logic.

Here's a complete, executable, testable Spring Boot application
(implementing a simple string manipulation):

[source,java]
----
@SpringBootApplication
public class Application {

  @Bean
  public Function<String, String> uppercase() {
    return value -> value.toUpperCase();
  }

  public static void main(String[] args) {
    SpringApplication.run(Application.class, args);
  }
}
----

It's just a Spring Boot application, so it can be built, run and
tested, locally and in a CI build, the same way as any other Spring
Boot application. The `Function` is from `java.util` and `Flux` is a
https://www.reactive-streams.org/[Reactive Streams] `Publisher` from
https://projectreactor.io/[Project Reactor]. The function can be
accessed over HTTP or messaging.

Spring Cloud Function has the following features:

* _Choice of programming styles - reactive, imperative or hybrid._
* _Function composition and adaptation (e.g., composing imperative functions with reactive)._
* _Support for reactive function with multiple inputs and outputs allowing merging, joining and other complex streaming operation to be handled by functions._
* _Transparent type conversion of inputs and outputs._
* _Packaging functions for deployments, specific to the target platform (e.g., Project Riff, AWS Lambda and more)_
* _Adapters to expose function to the outside world as HTTP endpoints etc._
* _Deploying a JAR file containing such an application context with an isolated classloader, so that you can pack them together in a single JVM._
* _Adapters for https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-aws[AWS Lambda], https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-azure[Azure], https://github.com/spring-cloud/spring-cloud-function/tree/master/spring-cloud-function-adapters/spring-cloud-function-adapter-gcp[Google Cloud Functions], and possibly other "serverless" service providers._