Spring MVC 4.2: New and Noteworthy

SPRINGONE2GXWASHINGTON, DC

Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under a Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/

Spring MVC 4.2:New and Noteworthy

Rossen Stoyanchev

Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/

About Me

• Spring Framework committer

• Spring MVC

• Spring WebSocket

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Demo Source

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https://github.com/rstoyanchev/s2gx2015-spring-mvc-42






HTTP Streaming

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Spring 3.2: Async Request Handling

• The ability to get off the Servlet container thread

• Take any controller method • replace return value T with DeferredResult<T>

• Range of use cases• long polling -- chat, live events• processing with latency -- scatter-gather, microservices

• Easy to introduce into existing apps

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Spring 4.0: WebSocket Messaging

• Full duplex messaging with SockJS emulation

• STOMP for application messaging• simple or external broker• @MessagingMapping methods for application work

• More advanced messaging needs• collaboration, games

• Very different from REST -- messaging architecture

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• Return ResponseBodyEmitter rather than @ResponseBody

• Or ResponseEntity<ResponseBodyEmitter>

• Stream of serialized Objects, emitted from any thread

• Objects serialized with HttpMessageConverter

Spring 4.2: HTTP Streaming

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Example@RequestMapping(path = "/stream", method = GET)public ResponseBodyEmitter startStream() { ResponseBodyEmitter emitter = new ResponseBodyEmitter();

... return emitter;}

// Later on emitter.send(foo, MediaType.APPLICATION_JSON);...emitter.send(bar, MediaType.APPLICATION_JSON);... emitter.complete();

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MediaType usedto select a converter


• Store ResponseBodyEmitter instances• in controller• in another component where events received

• Use onCompletion callback (on emitter) to remove instance

• Manual pub-sub to connected users

• Compare to STOMP + WebSocket• messaging protocol with built-in pub-sub

Pub-Sub

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• Return SseEmitter, an extension of ResponseBodyEmitter

• HTTP streaming with event markup

Spring 4.2: Server-Sent Events

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Example@RequestMapping(path = "/stream", method = GET)public SseEmitter startStream() { SseEmitter emitter = new SseEmitter();

... return emitter;}

// Later on emitter.send(event().event().id("id").name("type").data(foo));...emitter.complete();

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Spring 4.2: Direct Streaming• No serialization with HttpMessageConverter

• Stream directly to the response

• Return StreamingResponseBody instead of @ResponseBody

• ResponseEntity<StreamingResponseBody>

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Example@RequestMapping(path = "/stream", method = GET)public StreamingResponseBody handle() {

return new StreamingResponseBody() {

@Override public void writeTo(OutputStream os) throws IOException { os.write(...); os.flush(); } };}

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HTTP Streaming vs WebSocket Messaging• HTTP Streaming / SSE -- suited for simple streaming needs

• metrics, feeds

• STOMP / WebSocket scales to more advanced needs• finance, collaboration, games

• SockJS has lots of built-in smarts• fallback to polling if network/proxy prevents streaming• the extra mile for extra range of browsers

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CORS

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CORS Overview• Browsers prohibit requests to a different domain

• e.g. evil.com → bank.com

• CORS is a W3C specification for cross-domain requests

• For “simple” methods (GET, HEAD, POST)• browser sets Origin header

• Otherwise “preflight” request to obtain permission• HTTP OPTIONS• Origin and Access-Control-Request-Method headers

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http://www.w3.org/TR/cors/#simple-cross-origin-request


CORS Support in Spring?• Tomcat, Jetty, others provide CORS Filter implementations

• First-class support within Spring however still beneficial

• More fine-grained control (based on request mappings)

• Layer central + local configuration

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Local Configuration for @Controller• New @CrossOrigin annotation

• Supported on individual @RequestMapping methods

• Inherited from the class level

• Easy to configure one method or entire controller class hierarchy

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Local Configuration for Simple Handlers• Implement CorsConfigurationSource

• Two built-in handlers that make use this contract• ResourceHttpRequestHandler • SockJsHttpRequestHandler

public interface CorsConfigurationSource { CorsConfiguration getCorsConfiguration(HttpServletRequest req);}

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Central Configuration• The MVC Java config and MVC namespace expose CORS configuration

• Centralized configuration alternative• URL patterns based

• Layer central + local configuration• e.g. define general policy (e.g. allow csrf-token header)• refine locally

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More on CORS Configuration• AbstractHandlerMapping drives overall CORS handling

• It’s an internal feature that’s always on• cross-domain not allowed by default (as before)

• DispatcherServlet allows preflight requests in for handling• no need to set dispatchOptionsRequest

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Spring MVC CORS and Spring Security• DispatcherServlet now provides CORS handling

• Spring Security needs to open HTTP OPTIONS (for preflight requests)

• There is work planned to improve this• only allow preflight requests with Spring MVC

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https://jira.spring.io/browse/SEC-3025


CorsFilter • Filter-based approach to CORS configuration

• Comparable to Tomcat, Jetty filters

• CORS handling strictly before DispatcherServlet

• CorsFilter can/should be ordered before Spring Security Filter chain

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HTTP Caching

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Goals• Update default settings in line with current browsers/proxies

• Improve options local to @MVC controllers

• Provide use-case oriented + advanced config

• Various other improvements• Cache-Control directives, eTag/LastModified support

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CacheControl• Convenient “Cache-Control” response header value builder

• Covers the common use cases• CacheControl.maxAge(...)# cache for...• CacheControl.noStore() # prevent cache• CacheControl.noCache() # conditional cache + eTag/lastModified

• And the advanced• CacheControl.maxAge(...).noTransform().cachePublic()

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WebContentGenerator• Central HTTP cache configuration class

• WebContentInterceptor, ResourceHttpRequestHandler

• Defaults settings revised• no more HTTP 1.0 headers (“Expires” and “Pragma”)• cacheSeconds shortcut relies CacheControl

• Accepts CacheControl builder for its configuration

• Plus existing cacheSeconds shortcut (becomes CacheControl)

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http://docs.spring.io/spring-framework/docs/4.2.0.BUILD-SNAPSHOT/javadoc-api/org/springframework/web/servlet/support/WebContentGenerator.html#setCacheSeconds-int-


@MVC• ResponseEntity supports HTTP cache settings

ResponseEntity.ok().cacheControl(CacheControl.maxAge(30, TimeUnit.DAYS)).eTag(version) // lastModified also available.body(book);

• Sets response headers + checks client conditional headers

• Sends 304 (“not modified”) if eTag matches

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@MVC Continued• Explicit eTag / lastModified checks also possible

@RequestMappingpublic Object handle(WebRequest request) { long lastModified = ... if (request.checkNotModified(lastModified)) { return null; } // ... }

• Possible to check both eTag + lastModified (per recommendation)• request.checkNotModified(eTag,lastModified)

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Resource Handling• Extended HTTP cache control for serving static resources

• MVC Java config• ResourceHandlerRegistry accepts CacheControl

• MVC XML namespace• <mvc:cache-control> element within <mvc:resources>

• eTag added when VersionResourceResolver is configured

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Additional Reading• HTTP Caching Tutorial by Mark Nottingham

• Reference documentation HTTP Caching Support

• Notes in Migration from earlier versions wiki page

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https://www.mnot.net/cache_docs/

https://www.mnot.net/cache_docs/

http://docs.spring.io/spring-framework/docs/current/spring-framework-reference/html/mvc.html#mvc-caching

https://github.com/spring-projects/spring-framework/wiki/Migrating-from-earlier-versions-of-the-Spring-Framework


Composable@RequestMapping

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Custom @RequestMapping• For example:

@PostJson("/input")public Object handle() { return … ;}

• Given custom annotation:

@RequestMapping(method=GET, produces="application/json")public @interface PostJson { String value() default "";}

•

•

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Spring Shortcut Annotations? • Proposal to provide built-in shortcut annotations

• The challenge is finding the right mix

• Feedback based on specific use cases would help greatly

• SPR-13442 and spring-composed project

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https://jira.spring.io/browse/SPR-13442

https://github.com/sbrannen/spring-composed

https://jira.spring.io/browse/SPR-13442


Jackson

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Selective Serialization with @JsonView• Supported on @RequestMapping methods (since 4.1)

@RequestMapping @JsonView(SummaryView.class)public ResponseEntity<Foo> handle() { // … }

• Now also with @RequestBody

@RequestMapping(method = POST)public void handle(@JsonView(SummaryView.class) @RequestBody Foo foo) { // ...}

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Jackson Modules• Jackson2ObjectMapperBuilder auto-registers Jackson modules

• jdk7, joda, jsr310, jdk8

• Conditional on classpath detection of target dependencies

• Both MVC Java config and XML namespace use Jackson2ObjectMapperBuilder

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https://github.com/FasterXML/jackson-datatype-jdk7

https://github.com/FasterXML/jackson-datatype-joda

https://github.com/FasterXML/jackson-datatype-jsr310




@MVC

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Programming Model • HandlerMethod argument for @ExceptionHandler methods

• could be handy with @ControllerAdvice

• CharSequence as controller method return value (alternative to String)• groovy.lang.GString, StringBuilder, StringBuffer

• @InitBinder methods can register Formatter for specific field(s)• otherwise typically global in ConversionService

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Async Return Value Types• Built-in support for

• org.springframework.util.concurrent.ListenableFuture (4.1)• java.util.concurrent.CompletionStage (4.2)

• Both adapted to DeferredResult

• Easy to adapt others• RxJava Observable, Reactor Stream, …

• Follow example of built-in types

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JavaScript Templating

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Why?• Traditionally HTML served then enhanced with JavaScript

• Trend towards generating the UI with JavaScript

• Address challenges for single-page apps

• As well as mobile devices

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React JavaScript Library• Developed at Facebook and Instagram

• Virtual DOM with automatic DOM updates, fast, efficient

• Supports server-side rendering (outside of DOM)

• Fast adoption by major Internet players• Facebook/Instagram, Yahoo!, Netflix, Airbnb, etc.

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Server-Side Rendering• For React adopters, server-side rendering has significant benefits

• Faster load time, pre-generated HTML for web apps

• Search-engine friendly

• Client-centric UI still possible (e.g. Phonegap)

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Spring 4.2 and React• New view templating choice for JSR-223 scripting engines

• ScriptTemplateView , ViewResolver, and Configurer

• Configuration very similar to the alternatives (e.g. FreeMarker)

• Use with Nashorn JavaScript engine from JDK 8

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Additional Talks

Isomorphic Templating With Spring Boot, Nashorn and React

by Sebastien Deleuze

Comparing Hot JavaScript Frameworks: AngularJS, Ember.js and React.js by Matt Raible

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https://2015.event.springone2gx.com/schedule/sessions/isomorphic_templating_with_spring_boot_nashorn_and_react.html

https://2015.event.springone2gx.com/schedule/sessions/isomorphic_templating_with_spring_boot_nashorn_and_react.html

https://2015.event.springone2gx.com/schedule/sessions/comparing_hot_javascript_frameworks_angularjs_ember_js_and_react_js.html

https://2015.event.springone2gx.com/schedule/sessions/comparing_hot_javascript_frameworks_angularjs_ember_js_and_react_js.html


HTTP Byte Ranges

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Byte Ranges• HTTP 1.1 supports ability to download partial content

• RFC 7233

• Server advertises willingness via Accept-Ranges response header

• Client can then send a Range request header• e.g. Range: bytes=500-999

• Large media files, request any part / resume …

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http://tools.ietf.org/html/rfc7233

http://tools.ietf.org/html/rfc7233


Byte Range Support in Spring 4.2• HttpRange to create and parse ranges

• Accept-Range and Range exposed in HttpHeaders

• ResourceHttpRequestHandler supports byte ranges• e.g. server video files to iOS devices

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$ curl -v --range 0-99 \ http://localhost:8080/assets/jquery-2.1.4.js

> GET /assets/jquery-2.1.4.js HTTP/1.1> Range: bytes=0-99...< HTTP/1.1 206 Partial Content< ...< Accept-Ranges: bytes< Content-Range: bytes 0-99/247597< Content-Length: 100< ...

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Example


Client Side

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RestTemplate with OkHttp• RestTemplate + AsyncRestTemplate can be used with OkHttp

• lightweight HTTP library

• HTTP library support• JDK• Apache HttpComponents• Netty • OkHttp

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Flexible URI Template Handling• UriTemplateHandler for use with RestTemplate

• Default implementation delegates to UriComponentsBuilder

• Can be configured to• insert prefix in all URI templates• switch from path to path segment encoding by default

• Potential to plug in 3rd party URI template library• e.g. full RFC 6570 syntax

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WebSocket Messaging

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Simple Broker: Heartbeats@Configuration@EnableWebSocketMessageBrokerstatic class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer {

// …

@Overridepublic void configureMessageBroker(MessageBrokerRegistry registry) { registry.enableSimpleBroker("/topic").setTaskScheduler(scheduler());}

@Bean @Primarypublic TaskScheduler scheduler() { return new ThreadPoolTaskScheduler();}

}

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Enable


Simple Broker: Selector Expression

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• Add selector header on subscribe

client.subscribe("/topic/interval", function(message) { // ... }, {'selector' : 'headers.parity == \'even\''});

• SpEL expression evaluated against messages

• Only matching messages received


Multi-Server User Destinations

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• Spring supported special STOMP destination

• /user/{username}/…

• User receives message if connected

• User can be connected to any application server (since 4.2)


Multi-Server User Destinations

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Spring App

RabbitMQ

Browser

Sergi

/user/sergi/…


Connected User Information• SimpUserRegistry bean

• Expose information about connected users and subscriptions

• Supported in multi-server scenarios• via UserRegistryMessageHandler

• Broadcast local user registry to other servers (via broker relay)• every 10 seconds• remote registry info expires after 20 seconds

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STOMP Client• Supported over WebSocket + over TCP

• Plug in any Spring WebSocketClient implementation

• SockJsClient allows using STOMP over WebSocket/SockJS

• Support for heartbeats, receipts

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Programming Model• Property placeholders for @MessageMapping methods

• @JsonView on @Payload arguments

• Destination template variables in @SendTo annotation

• Async return value types• org.springframework.util.concurrent.ListenableFuture • CompletableFuture/CompletionStage (JDK 8)

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Programming Model• @ControllerAdvice + @MessageExceptionHandler methods

• HandlerMethod arguments for @MessageExceptionHandler

• Spring OXM Marshaller based MessageConverter

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Related Talk

From Zero to Hero with Spring WebSocket

by Sergi Almar

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https://2015.event.springone2gx.com/schedule/sessions/from_zero_to_hero_with_spring_websocket.html

https://2015.event.springone2gx.com/schedule/sessions/from_zero_to_hero_with_spring_websocket.html

Unless otherwise indicated, these slides are © 2013-2014 Pivotal Software, Inc. and licensed under aCreative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ 64

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Spring MVC 4.2: New and Noteworthy

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