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Added function composition documentation

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Oleg Zhurakousky
2019-11-04 13:06:24 +01:00
parent 00ec268aca
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docs/src/main/asciidoc/spring-cloud-function.adoc
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@@ -116,6 +116,35 @@ needed. If you want to use a different package, you can set
`spring.cloud.function.scan.enabled=false` to switch off the scan
completely.
=== Function Composition
Function Composition is a feature that allows one to compose several functions into one.
The core support is based on function composition feature available with https://docs.oracle.com/javase/8/docs/api/java/util/function/Function.html#andThen-java.util.function.Function-[Function.andThen(..)]
support available since Java 8. However on top of it, we provide few additional features.
==== Declarative Function Composition
This feature allows you to provide composition instruction in a declarative way using `|` (pipe) or `,` (comma) delimiter
when providing `spring.cloud.function.definition` property.
For example
----
--spring.cloud.function.definition=uppercase|reverse
----
Here we effectively provided a definition of a single function which itself is a composition of
function `uppercase` and function `reverse`. In fact that is one of the reasons why the property name is _definition_ and not _name_,
since the definition of a function can be a composition of several named functions.
And as mentioned you can use `,` instead of pipe (such as `...definition=uppercase,reverse`).
==== Composing non-Functions
Spring Cloud Function also supports composing Supplier with `Consumer` or `Function` as well as `Function` with `Consumer`.
What's important here is to understand the end product of such definitions.
Composing Supplier with Function still results in Supplier while composing Supplier with Consumer will effectively render Runnable.
Following the same logic composing Function with Consumer will result in Consumer.
And of course you can't compose uncomposable such as Consumer and Function, Consumer and Supplier etc.
=== Function Routing
Since version 2.2 Spring Cloud Function provides routing feature allowing