In Spring Framework 5.0, we introduced a new, functional web framework, next to the existing annotation-driven programming model. In this talk, we will discuss this new framework: how it is used, what its goals are, how it compares to the annotation model, and other related topics. Presenter : Arjen Poutsma, Pivotal

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New in Spring 5:
Functional Web Framework
Arjen Poutsma
Pivotal

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About Arjen
•Twenty years of experience in Enterprise Software
Development
•Joined SpringSource in 2005
•Development lead of Spring Web Services, Spring MVC, Spring
Scala
•Working on Spring 5

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I do like annotations...

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...but there are downsides
•“Magic”
•No link between data and behavior
•Reflection
•Performance
•Type Erasure

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Design Goals
•Functional Style
•java.util.function
•java.util.stream
•More library; less framework
•Explicit
•Customizable
•No reflection

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Functional Programming
(in Java 8)

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Immutability
•No change after construction
•Builders
•Thread-safety
•e.g. String
•toUpperCase()
•StringBuilder

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First-class Functions
•Functions as first-class citizens
•Functions as arguments
•Functions as return value
•Reusability
•e.g. String
•indexOf(char) vs indexOf(Predicate<Char>)

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Pure Functions
•Same result given same arguments
•No Limit side effects
•Application boundaries
•Testability
•Cacheability
•Parallelization

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Demo

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Function<ServerRequest, Mono<? extends ServerResponse>>
HandlerFunction

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ServerRequest
•Similar to RequestEntity
•Immutable
•Headers
• Optional<MediaType> contentType()
• List<String> header(String)
•Body
• Mono<T> bodyToMono(Class<T>)

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ServerResponse
•Similar to ResponseEntity
•Immutable w/ Builder
•Headers
• lastModified(ZonedDateTime)
• header(String, String...)
•Body
• body(Publisher<T>, Class<T>)

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Function<ServerRequest, Mono<HandlerFunction<? extends ServerResponse>>
RouterFunction

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RouterFunctions

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RequestPredicate
Predicate<ServerRequest>

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RequestPredicates
•Common predicates
•path
•headers (Content-Type, Accept)
•Build (compose) your own!

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BiFunction<Request,
HandlerFunction<? extends ServerResponse>,
Mono<? extends ServerResponse>>
HandlerFilterFunction

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Running Router Functions
• RouterFunction as @Bean in @EnableWebFlux class
•Convert RouterFunction to HttpHandler
•Reactor Netty
•Tomcat
•Servlet 3.1+
•Undertow

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Demo

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Summary
•Handler functions handle request by returning a response
•Router functions route to handler functions
•Router functions can be filtered by filter functions
•Router functions can be run in a reactive web runtime

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Q & A
Resources
•Sample: https://github.com/poutsma/web-function-sample
•Blog post: https://spring.io/blog/2016/09/22/new-in-spring-5-
functional-web-framework
•Kotlin: https://speakerdeck.com/sdeleuze/functional-web-
applications-with-spring-and-kotlin
•Reactor: http://projectreactor.io/learn