Spring Framework 5.0 Themes and Trends

Spring Framework 5.0
Themes and Trends
Sébastien Deleuze @sdeleuze
Brian Clozel @bclozel

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Unless otherwise indicated, these slides are © 2013-2015 Pivotal Software, Inc. and licensed under a 
Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
Spring Framework 5
‣ Reactive foundations
‣ Spring WebFlux
‣ Kotlin builtin support
‣ Functional bean registration
‣ Baseline upgrade & cleanup
‣ Java 9 support
‣ Performance improvements
2

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Reactive foundations

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Why going Reactive?
4
More for scalability and 
stability than for speed

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What issue are we trying to solve?
5
1 request = 1 thread

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From blocking to event-based
6
Neutral to latency

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Reactive Streams
7
Publisher Subscriber
Backpressure
request(n) data
0..N data then
0..1 (Error | Complete)

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9

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Reactive Streams is 4 interfaces (and a TCK)
11
public interface Publisher {
void subscribe(Subscriber super T> s);
}
public interface Subscriber {
void onSubscribe(Subscription s);
void onNext(T t);
void onError(Throwable t);
void onComplete();
}
public interface Subscription {
void request(long n);
void cancel();
}
public interface Processor extends Subscriber, Publisher {
}

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Spring Framework 5 uses Reactor
for its Reactive foundations
Reactor, RxJava, Akka Streams, etc.
12
Reactive libraries
Your web application can use

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Flux
• Implements Reactive Streams Publisher
• 0 to n elements
• Operators: flux.map(…).zip(…).flatMap(…)
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Mono
• Implements Reactive Streams Publisher
• 0 to 1 element
• Operators: mono.then(…).otherwise(…)
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StepVeriﬁer
15
StepVerifier.create(flux) 
.expectNext("foo", "bar") 
.verifyComplete();
‣ Designed to test easily Reactive Streams Publishers
‣ Carefully designed after writing thousands of
Reactor and Spring WebFlux tests

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Blocking versus Reactive API
16
interface ReactiveUserRepository {
Mono findOne(String id);
Flux findAll();
Mono save(Mono user);
}
interface UserRepository {
User findOne(String id);
List findAll();
void save(User user);
}
Blocking API Reactive API
‣ Method returns when all the data has 
been received
‣ Exceptions thrown when an error occurs
‣ Method returns immediately
‣ Error event instead of throwing exception
‣ Complete event instead of method return
‣ Mono = error or success, no data
‣ Data comes as events too the 
Mono or Flux return value

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Upcoming high-level features
17

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Spring WebFlux

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spring-webmvc
@Controller, @RequestMapping
Servlet API
Servlet Container
spring-webflux
HTTP / Reactive Streams
Servlet 3.1, Netty, Undertow
Router Functions

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Spring MVC
20
@RestController
public class UserController {
private final UserRepository repo;
public UserController(UserRepository repo) { this.repo = repo; }
@GetMapping("/user/{id}")
public User findOne(@PathVariable String id) { return repo.findOne(id); }
@GetMapping("/user")
public List findAll() { return repo.findAll(); }
@PostMapping("/user")
public void save(@RequestBody User user) { repo.save(user); }
}
User findOne(String id);
List findAll();
void save(User user);
}

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WebFlux annotation-based server
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@RestController
public class ReactiveUserController {
private final ReactiveUserRepository repo;
public ReactiveUserController(ReactiveUserRepository repo) { this.repo = repo; }
public Mono findOne(@PathVariable String id) { return repo.findOne(id); }
public Flux findAll() { return repo.findAll(); }
public Mono save(@RequestBody Mono user) { repo.save(user); }
}
Mono findOne(String id);
Flux findAll();
Mono save(Mono user);
}

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Flux: array versus stream
22
JSON
application/json
JSON Streaming
application/stream+json
Server-Sent Events
text/event-stream
[
{"a": "foo", "b": "bar"},
{"a": "baz", "b": "boo"}
]
‣ Single Jackson invocation
‣ Doesn’t support infinite streams
{"a": "foo", "b": "bar"}
{"a": "baz", "b": "boo"}
…
‣ Jackson invocation per element
‣ Supports infinite streams
data: {"a": "foo", "b": "bar"}
data: {"a": "baz", "b": "boo"}
…
public Flux findAll()

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WebFlux functional API
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‣ Reactive
‣ Client and server
‣ Lightweight
‣ Flexible
‣ Can be use with or without dependency injection!
‣ Simple functional building blocks

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WebFlux functional server API
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‣ RouterFunction
Mono>
route(ServerRequest request)
‣ RequestPredicate
boolean test(ServerRequest request)
‣ HandlerFunction
Mono handle(ServerRequest request)
‣ HandlerFilterFunction
Mono filter(ServerRequest request,
HandlerFunction next)

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WebFlux functional server API
25
@Controller
public class UserController {
public RouterFunction route() {
return RouterFunctions
.route(GET("/users"), this::listUsers)
.andRoute(POST("/users"), this::createUser);
}
Mono listUsers(ServerRequest request) { ... }
Mono createUser(ServerRequest request) { ... }
}

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RequestPredicates
26
‣ HTTP method
‣ Path
‣ Path prefix
‣ Path extension
‣ Headers
‣ Content type
‣ Accept
‣ Query param

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New WebClient API
27
WebClient client = WebClient.create();
Mono githubUser = client
.get()
.uri("https://api.github.com/users/{username}", username)
.exchange()
.then(response -> response.bodyToMono(GithubUser.class));
Mono twitterUser = client
.get()
.uri("https://api.twitter.com/1.1/users/show.json?screen_name={username}", username)
.exchange()
.then(response -> response.bodyToMono(TwitterUser.class));
return githubUser.and(twitterUser, (github, twitter)-> new AppUser(github, twitter));

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WebFlux demo

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WebFlux Streaming Showcase
29
https://github.com/bclozel/webflux-streaming-showcase
quote-stream
streaming-service
GET /quotes 
"application/stream+json"
GET /quotes/feed 
"text/event-stream"
MongoDB

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Kotlin Support

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Kotlin
‣ Overcome Java limitations
‣ Elegant and pragmatic language
‣ Concise code
‣ Simple and easy to learn
‣ Very good Java interoperability
‣ Embrace both functional and object
oriented programming
31

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How does it compare with …
32
Same conciseness and expressive code, 
but Kotlin default static typing and null-safety 
make a big diﬀerence.
"Kotlin is a software engineering language in contrast
to Scala which is a computing science language." 
Eric Kolotyluk, Electronic Arts, Scala developer
Swift Swift and Kotlin share similar syntax. Swift is coming
from native world while Kotlin is coming from JVM
world.

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Domain model classes
33
public class User {
private String userName;
private String firstName;
private String lastName;
private Point location;
public User(String userName, String firstName, String lastName) {
this(userName,firstName, lastName, null);
}
public User(String userName, String firstName, String lastName, Point location) {
Assert.notNull(userName);
Assert.notNull(firstName);
Assert.notNull(lastName);
this.userName = userName;
this.firstName = firstName;
this.lastName = lastName;
this.location = location;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public Point getLocation() {
return location;
}
public void setLocation(Point location) {
this.location = location;
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
UserJ j = (UserJ) o;
if (!userName.equals(j.userName)) {
return false;
}
if (!firstName.equals(j.firstName)) {
return false;
}
if (!lastName.equals(j.lastName)) {
return false;
}
return location != null ? location.equals(j.location) : j.location == null;
}
@Override
public int hashCode() {
int result = userName.hashCode();
result = 31 * result + firstName.hashCode();
result = 31 * result + lastName.hashCode();
result = 31 * result + (location != null ? location.hashCode() : 0);
return result;
}
@Override
public String toString() {
return "User{" +
"userName='" + userName + '\'' +
", firstName='" + firstName + '\'' +
", lastName='" + lastName + '\'' +
", location=" + location +
'}';
}
}
data class User( 
val userName: String, 
val firstName: String?, 
val lastName: String?, 
val location: Point = Point(0, 0) 
)
Generates equals()
and hashcode()
val = immutable
var = mutable
String? = nullable
String = non-nullable
Optional parameter
with default value
Constructor +
properties declaration

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Kotlin is much more than a 
"super Java" or than Lombok
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My favorite Kotlin features
‣ Awesome type inference with static typing
‣ Extensions
‣ Reified type parameters
‣ Null safety
‣ Type aliases
‣ Allows to write nice DSL
‣ Smart casts
35

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Spring Initializr
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https://start.spring.io/#!language=kotlin

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Introducing Kotlin support in Spring Framework 5
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https://goo.gl/gMnhxN

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Gradle build ﬁles written in Kotlin
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kotlin-spring Gradle and Maven plugin
39
@SpringBootApplication
open class Application {
@Bean
open fun foo() = ...
@Bean
open fun bar() = ...
}
Without kotlin-spring
@SpringBootApplication
class Application {
@Bean
fun foo() = ...
@Bean
fun bar() = ...
}
With kotlin-spring
Also available as a kotlin-allopen generic plugin

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kotlin-noarg Gradle and Maven plugin
40
configure { 
annotation("org.springframework.data.mongodb.core.mapping.Document") 
}
Also available preconfigured for JPA as kotlin-jpa
@Document
data class User(
@Id val login: String,
val firstname: String,
val lastname: String,
val email: String,
val company: String? = null,
val description: Map = emptyMap(),
val logoUrl: String? = null,
val role: Role = Role.ATTENDEE)

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Persistence
41
class EventRepository(val template: ReactiveMongoTemplate) {
fun findAll() = template.find(Query().with(Sort("year")))
fun findOne(id: String) = template.findById(id)
fun deleteAll() = template.remove(Query())
fun save(event: Event) = template.save(event)
}

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Extensions
42
// Spring Boot extensions
fun run(type: KClass<*>, vararg args: String) = SpringApplication.run(type.java, *args)
// Spring Data extensions
inline fun ReactiveMongoOperations.findById(id: Any): Mono =
findById(id, T::class.java)
inline fun ReactiveMongoOperations.find(query: Query): Flux =
find(query, T::class.java)
inline fun ReactiveMongoOperations.findAll(): Flux =
findAll(T::class.java)
inline fun ReactiveMongoOperations.findOne(query: Query): Mono =
find(query, T::class.java).next()
inline fun ReactiveMongoOperations.remove(query: Query): Mono =
remove(query, T::class.java)
// Other extensions
fun ServerRequest.language() =
Language.findByTag(this.headers().header(HttpHeaders.ACCEPT_LANGUAGE).first())

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Spring MVC
43
@RestController
class UserController(val repo: UserRepository) {
fun findOne(@PathVariable id: String) = repo.findOne(id)
fun findAll() = repo.findAll()
fun save(@RequestBody user: User) = repo.save(user)
}
fun findOne(id: String): User
fun findAll(): List
fun save(user: User)
}
Classes and functions are public by default
Static typing + type inference
Constructor injection
without @Autowired if
single constructor

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Spring WebFlux annotation-based
44
@RestController
class ReactiveUserController(val repository: ReactiveUserRepository) {
fun findOne(@PathVariable id: String) = repository.findOne(id)
fun findAll() = repository.findAll()
fun save(@RequestBody user: Mono) = repository.save(user)
}
fun findOne(id: String): Mono
fun findAll(): Flux
fun save(user: Mono): Mono
}

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Spring WebFlux functional Kotlin DSL
45
router {
"/blog" { findAllView(it) }
"/blog/{slug}" { findOneView(it) }
"/api/blog" { findAll(it) }
"/api/blog/{id}" { findOne(it) }
}
Simple path request predicate

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router {
GET("/blog") { findAllView(it) }
GET("/blog/{slug}") { findOneView(it) }
GET("/api/blog") { findAll(it) }
GET("/api/blog/{id}") { findOne(it) }
POST("/api/blog") { create(it) }
}
HTTP method + path predicate

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router {
GET("/blog", blogController::findAllView)
GET("/blog/{slug}", blogController::findOneView)
GET("/api/blog", blogController::findAll)
GET("/api/blog/{id}", blogController::findOne)
POST("/api/blog", blogController::create)
}
Method references

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48
router {
"/blog".nest {
GET("/", blogController::findAllView)
GET("/{slug}", blogController::findOneView)
}
"/api/blog".nest {
GET("/", blogController::findAll)
GET("/{id}", blogController::findOne)
POST("/", blogController::create)
}
}
Nested routing

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49
router {
("/blog" and accept(TEXT_HTML)).nest {
GET("/", blogController::findAllView)
GET("/{slug}", blogController::findOneView)
}
("/api/blog" and accept(APPLICATION_JSON)).nest {
GET("/", blogController::findAll)
GET("/{id}", blogController::findOne)
POST("/", blogController::create)
}
}
Rich set of RequestPredicate

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Leveraging Kotlin nullable information
50
// "GET /foo" and "GET /foo?bar=baz" are allowed
@GetMapping("/foo")
fun foo(@RequestParam bar: String?) = ...
// "GET /foo?bar=baz" is allowed and "GET /foo" will return an error
@GetMapping("/foo")
fun foo(@RequestParam bar: String) = ...

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Spring Kotlin extensions
51
Mono findAll(ServerRequest request) {
return ServerResponse.ok().body(repository.findAll(), User.class);
}
fun findAll(req: ServerRequest) = ok().body(repository.findAll())
No need to specify explicitly types
thanks to Kotlin reified type parameters
inline fun ServerResponse.BodyBuilder.body(publisher: Publisher) =
body(publisher, T::class.java)
ServerResponseExtensions provided in spring-webflux.jar

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Spring Framework extensions
52
‣ ApplicationContext
‣ Spring WebFlux
• Client
• Server
‣ Spring MVC
‣ RestTemplate
‣ JDBC
‣ Reactor (via reactor-kotlin)

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Kotlin type-safe templates
53
import io.spring.demo.*
"""
${include("header")}
${i18n("title")}

${users.joinToLine{ "${i18n("user")} ${it.firstname} ${it.lastname}" }}

${include("footer")}
"""
See https://github.com/sdeleuze/kotlin-script-templating for more details
‣ Regular Kotlin code, no new dialect to learn
‣ Extensible, refactoring and auto-complete support
‣ Need to cache compiled scripts for good performances

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Tests with JUnit
54
class UserIntegrationTests : AbstractIntegrationTests() {
@Test
fun `Find Dan North`() {
val speaker = client.get()
.uri("/api/speaker/tastapod")
.accept(APPLICATION_JSON)
.exchange().then { r -> r.bodyToMono() }
StepVerifier.create(speaker)
.consumeNextWith {
assertEquals("North", it.lastname)
assertTrue(it.role == Role.SPEAKER)
}
.verifyComplete()
}
}

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JUnit 5 will improve Kotlin support
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MiXiT reference web application
56
https://github.com/mixitconf/mixit

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Functional bean registration

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Functional bean registration API
‣ After XML and JavaConfig, a third major way to register your beans
‣ Lambda with Supplier act as a FactoryBean
‣ Very efficient, no reflection, no CGLIB proxies involved
‣ Usable with pure Spring Framework apps, not yet with Spring Boot
58

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API example
59
GenericApplicationContext context = new GenericApplicationContext();
context.registerBean(A.class);
context.registerBean(B.class, () -> new B(context.getBean(A.class)));
GenericApplicationContext {
registerBean()
registerBean { B(it.getBean()) }}

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Choose the ﬂavour you prefer!
60
Boot + WebFlux
WebFlux +
functional bean registration
‣ Automatic server configuration
‣ All Spring Boot goodness!
‣ Bean registration
• Annotation-based
• Optimized Classpath scanning
‣ Reference webapp startup:
• 3 seconds
• 20 Mbytes heap size after GC
‣ Manual server configuration
‣ Bean registration
• Lambda-based
• No Cglib proxy
• No need for kotlin-spring plugin
‣ Reference webapp startup:
• 1.2 seconds
• 10 Mbytes heap size after GC

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See functional-bean-registration MiXiT branch
61
https://goo.gl/iGwzw3
AnnotationConfigApplicationContext {
registerBean { ReactiveMongoTemplate(SimpleReactiveMongoDatabaseFactory(
ConnectionString(it.environment.getProperty("mongo.uri"))))
}
registerBean()
registerBean()
registerBean()
registerBean()
registerBean()
// ...
}

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Spring Framework 5.0 Themes and Trends

Spring Framework 5.0 Themes and Trends

Sébastien Deleuze

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