spring-cloud-function/README.adoc

// Do not edit this file (e.g. go instead to src/main/asciidoc)

image::https://travis-ci.org/spring-cloud/spring-cloud-function.svg?branch=master[Build Status, link=https://travis-ci.org/spring-cloud/spring-cloud-function]

== 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<Flux<String>, Flux<String>> uppercase() {
    return flux -> flux.map(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
http://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 4 main features:

1. Wrappers for `@Beans` of type `Function`, `Consumer` and
`Supplier`, exposing them to the outside world as either HTTP
endpoints and/or message stream listeners/publishers with RabbitMQ, Kafka etc.

2. Compiling strings which are Java function bodies into bytecode, and
then turning them into `@Beans` that can be wrapped as above.

3. Deploying a JAR file containing such an application context with an
isolated classloader, so that you can pack them together in a single
JVM.

4. 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-openwhisk[Apache OpenWhisk] and possibly other "serverless" service providers.

== Getting Started

Build from the command line (and "install" the samples):

----
$ ./mvnw clean install
----

(If you like to YOLO add `-DskipTests`.)

Run one of the samples, e.g.

----
$ java -jar spring-cloud-function-samples/function-sample/target/*.jar
----

This runs the app and exposes its functions over HTTP, so you can
convert a string to uppercase, like this:

----
$ curl -H "Content-Type: text/plain" localhost:8080/uppercase -d Hello
HELLO
----

You can convert multiple strings (a `Flux<String>`) by separating them
with new lines

----
$ curl -H "Content-Type: text/plain" localhost:8080/uppercase -d 'Hello
> World'
HELLOWORLD
----

(You can use `^Q^J` in a terminal to insert a new line in a literal
string like that.)

== Building and Running a Function

The sample `@SpringBootApplication` above has a function that can be
decorated at runtime by Spring Cloud Function to be an HTTP endpoint,
or a Stream processor, for instance with RabbitMQ, Apache Kafka or
JMS.

The `@Beans` can be `Function`, `Consumer` or `Supplier` (all from
`java.util`), and their parametric types can be String or POJO. A
`Function` is exposed as a `Processor` if
`spring-cloud-function-stream` is on the classpath and a
`spring.cloud.function.stream.endpoint` property is configured in the
Spring environment. A `Consumer` is also exposed as an HTTP POST, or
as a Stream `Sink`. A `Supplier` translates to an HTTP GET, or a
Stream `Source`.

Functions can be of `Flux<String>` or `Flux<Pojo>` and Spring Cloud
Function takes care of converting the data to and from the desired
types, as long as it comes in as plain text or (in the case of the
POJO) JSON. TBD: support for `Flux<Message<Pojo>>` and maybe plain
`Pojo` types (Fluxes implied and implemented by the framework).

Functions can be grouped together in a single application, or deployed
one-per-jar. It's up to the developer to choose. An app with multiple
functions can be deployed multiple times in different "personalities",
exposing different functions over different physical transports.

== Deploying a Packaged Function

TBD: describe the deployer app.

== Dynamic Compilation

To run these examples, change into the `scripts` directory:

----
cd scripts
----

Also, start a RabbitMQ server locally (e.g. execute `rabbitmq-server`).

=== Start the Function Registry Service:

----
./function-registry.sh
----

=== Register a Function:

----
./registerFunction.sh -n uppercase -f "f->f.map(s->s.toString().toUpperCase())"
----

=== Run a REST Microservice using that Function:

----
./web.sh -f uppercase -p 9000
curl -H "Content-Type: text/plain" -H "Accept: text/plain" localhost:9000/uppercase -d foo
----

=== Register a Supplier:

----
./registerSupplier.sh -n words -f "()->Flux.just(\"foo\",\"bar\")"
----

=== Run a REST Microservice using that Supplier:

----
./web.sh -s words -p 9001
curl -H "Accept: application/json" localhost:9001/words
----

=== Register a Consumer:

----
./registerConsumer.sh -n print -t String -f "System.out::println"
----

=== Run a REST Microservice using that Consumer:

----
./web.sh -c print -p 9002
curl -X POST -H "Content-Type: text/plain" -d foo localhost:9002/print
----

=== Run Stream Processing Microservices:

First register a streaming words supplier:

----
./registerSupplier.sh -n wordstream -f "()->Flux.intervalMillis(1000).map(i->\"message-\"+i)"
----

Then start the source (supplier), processor (function), and sink (consumer) apps
(in reverse order):

----
./stream.sh -p 9103 -i uppercaseWords -c print
./stream.sh -p 9102 -i words -f uppercase -o uppercaseWords
./stream.sh -p 9101 -s wordstream -o words
----

The output will appear in the console of the sink app (one message per second, converted to uppercase):

----
MESSAGE-0
MESSAGE-1
MESSAGE-2
MESSAGE-3
MESSAGE-4
MESSAGE-5
MESSAGE-6
MESSAGE-7
MESSAGE-8
MESSAGE-9
...
----

== Building

:jdkversion: 1.7

=== Basic Compile and Test

To build the source you will need to install JDK {jdkversion}.

Spring Cloud uses Maven for most build-related activities, and you
should be able to get off the ground quite quickly by cloning the
project you are interested in and typing

----
$ ./mvnw install
----

NOTE: You can also install Maven (>=3.3.3) yourself and run the `mvn` command
in place of `./mvnw` in the examples below. If you do that you also
might need to add `-P spring` if your local Maven settings do not
contain repository declarations for spring pre-release artifacts.

NOTE: Be aware that you might need to increase the amount of memory
available to Maven by setting a `MAVEN_OPTS` environment variable with
a value like `-Xmx512m -XX:MaxPermSize=128m`. We try to cover this in
the `.mvn` configuration, so if you find you have to do it to make a
build succeed, please raise a ticket to get the settings added to
source control.

For hints on how to build the project look in `.travis.yml` if there
is one. There should be a "script" and maybe "install" command. Also
look at the "services" section to see if any services need to be
running locally (e.g. mongo or rabbit).  Ignore the git-related bits
that you might find in "before_install" since they're related to setting git
credentials and you already have those.

The projects that require middleware generally include a
`docker-compose.yml`, so consider using
http://compose.docker.io/[Docker Compose] to run the middeware servers
in Docker containers. See the README in the
https://github.com/spring-cloud-samples/scripts[scripts demo
repository] for specific instructions about the common cases of mongo,
rabbit and redis.

NOTE: If all else fails, build with the command from `.travis.yml` (usually
`./mvnw install`).

=== Documentation

The spring-cloud-build module has a "docs" profile, and if you switch
that on it will try to build asciidoc sources from
`src/main/asciidoc`. As part of that process it will look for a
`README.adoc` and process it by loading all the includes, but not
parsing or rendering it, just copying it to `${main.basedir}`
(defaults to `${basedir}`, i.e. the root of the project). If there are
any changes in the README it will then show up after a Maven build as
a modified file in the correct place. Just commit it and push the change.

=== Working with the code
If you don't have an IDE preference we would recommend that you use
http://www.springsource.com/developer/sts[Spring Tools Suite] or
http://eclipse.org[Eclipse] when working with the code. We use the
http://eclipse.org/m2e/[m2eclipse] eclipse plugin for maven support. Other IDEs and tools
should also work without issue as long as they use Maven 3.3.3 or better.

==== Importing into eclipse with m2eclipse
We recommend the http://eclipse.org/m2e/[m2eclipse] eclipse plugin when working with
eclipse. If you don't already have m2eclipse installed it is available from the "eclipse
marketplace".

NOTE: Older versions of m2e do not support Maven 3.3, so once the
projects are imported into Eclipse you will also need to tell
m2eclipse to use the right profile for the projects.  If you
see many different errors related to the POMs in the projects, check
that you have an up to date installation.  If you can't upgrade m2e,
add the "spring" profile to your `settings.xml`. Alternatively you can
copy the repository settings from the "spring" profile of the parent
pom into your `settings.xml`.

==== Importing into eclipse without m2eclipse
If you prefer not to use m2eclipse you can generate eclipse project metadata using the
following command:

[indent=0]
----
	$ ./mvnw eclipse:eclipse
----

The generated eclipse projects can be imported by selecting `import existing projects`
from the `file` menu.


== Contributing

Spring Cloud is released under the non-restrictive Apache 2.0 license,
and follows a very standard Github development process, using Github
tracker for issues and merging pull requests into master. If you want
to contribute even something trivial please do not hesitate, but
follow the guidelines below.

=== Sign the Contributor License Agreement
Before we accept a non-trivial patch or pull request we will need you to sign the
https://cla.pivotal.io/sign/spring[Contributor License Agreement].
Signing the contributor's agreement does not grant anyone commit rights to the main
repository, but it does mean that we can accept your contributions, and you will get an
author credit if we do.  Active contributors might be asked to join the core team, and
given the ability to merge pull requests.

=== Code of Conduct
This project adheres to the Contributor Covenant https://github.com/spring-cloud/spring-cloud-build/blob/master/docs/src/main/asciidoc/code-of-conduct.adoc[code of
conduct]. By participating, you  are expected to uphold this code. Please report
unacceptable behavior to spring-code-of-conduct@pivotal.io.

=== Code Conventions and Housekeeping
None of these is essential for a pull request, but they will all help.  They can also be
added after the original pull request but before a merge.

* Use the Spring Framework code format conventions. If you use Eclipse
  you can import formatter settings using the
  `eclipse-code-formatter.xml` file from the
  https://raw.githubusercontent.com/spring-cloud/spring-cloud-build/master/spring-cloud-dependencies-parent/eclipse-code-formatter.xml[Spring
  Cloud Build] project. If using IntelliJ, you can use the
  http://plugins.jetbrains.com/plugin/6546[Eclipse Code Formatter
  Plugin] to import the same file.
* Make sure all new `.java` files to have a simple Javadoc class comment with at least an
  `@author` tag identifying you, and preferably at least a paragraph on what the class is
  for.
* Add the ASF license header comment to all new `.java` files (copy from existing files
  in the project)
* Add yourself as an `@author` to the .java files that you modify substantially (more
  than cosmetic changes).
* Add some Javadocs and, if you change the namespace, some XSD doc elements.
* A few unit tests would help a lot as well -- someone has to do it.
* If no-one else is using your branch, please rebase it against the current master (or
  other target branch in the main project).
* When writing a commit message please follow http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html[these conventions],
  if you are fixing an existing issue please add `Fixes gh-XXXX` at the end of the commit
  message (where XXXX is the issue number).