Spring MVC 4.2: New and Noteworthy

SPRINGONE2GX
WASHINGTON, 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 a
Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/
About Me
• Spring Framework committer
• Spring MVC
• Spring WebSocket
2

Demo Source
3
https://github.com/rstoyanchev/
s2gx2015-spring-mvc-42

HTTP Streaming
4

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
5

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
6

• 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
7

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();
8
MediaType used
to 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
9

• Return SseEmitter, an extension of ResponseBodyEmitter
• HTTP streaming with event markup
Spring 4.2: Server-Sent Events
10

Example
public SseEmitter startStream() {
SseEmitter emitter = new SseEmitter();
...
return emitter;
}
// Later on
emitter.send(event().event().id("id").name("type").data(foo));
...
emitter.complete();
11

Spring 4.2: Direct Streaming
• No serialization with HttpMessageConverter
• Stream directly to the response
• Return StreamingResponseBody instead of @ResponseBody
• ResponseEntity<StreamingResponseBody>
12

Example
public StreamingResponseBody handle() {
return new StreamingResponseBody() {
@Override
public void writeTo(OutputStream os) throws IOException {
os.write(...);
os.flush();
}
};
}
13

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
14

CORS
15

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
16

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
17

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
18

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);
}
19

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
20

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
21

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
22

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
23

HTTP Caching
24

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
25

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()
26

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)
27

@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
28

@MVC Continued
• Explicit eTag / lastModified checks also possible
@RequestMapping
public Object handle(WebRequest request) {
long lastModified = ...
if (request.checkNotModified(lastModified)) {
return null;
}
// ...
}
• Possible to check both eTag + lastModified (per recommendation)
• request.checkNotModified(eTag,lastModified)
29

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
30

Additional Reading
• HTTP Caching Tutorial by Mark Nottingham
• Reference documentation HTTP Caching Support
• Notes in Migration from earlier versions wiki page
31

Composable
@RequestMapping
32

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 "";
}
33

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
34

Jackson
35

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) {
// ...
}
36

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
37

@MVC
38

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
39

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
40

JavaScript Templating
41

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
42

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.
43

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)
44

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
45

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
46

HTTP Byte Ranges
47

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 …
48

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
49

$ 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
< ...
50
Example

Client Side
51

RestTemplate with OkHttp
• RestTemplate + AsyncRestTemplate can be used with OkHttp
• lightweight HTTP library
• HTTP library support
• JDK
• Apache HttpComponents
• Netty
• OkHttp
52

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
53

WebSocket Messaging
54

Simple Broker: Heartbeats
@Configuration
@EnableWebSocketMessageBroker
static class WebSocketConfig extends AbstractWebSocketMessageBrokerConfigurer {
// …
@Override
public void configureMessageBroker(MessageBrokerRegistry registry) {
registry.enableSimpleBroker("/topic").setTaskScheduler(scheduler());
}
@Bean @Primary
public TaskScheduler scheduler() {
return new ThreadPoolTaskScheduler();
}
}
55
Enable

Simple Broker: Selector Expression
56
• 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
57
• 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
58
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
59

STOMP Client
• Supported over WebSocket + over TCP
• Plug in any Spring WebSocketClient implementation
• SockJsClient allows using STOMP over WebSocket/SockJS
• Support for heartbeats, receipts
60

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)
61

Programming Model
• @ControllerAdvice + @MessageExceptionHandler methods
• HandlerMethod arguments for @MessageExceptionHandler
• Spring OXM Marshaller based MessageConverter
62

Related Talk
From Zero to Hero with Spring WebSocket
by Sergi Almar
63

Creative Commons Attribution-NonCommercial license: http://creativecommons.org/licenses/by-nc/3.0/ 64
Thank You for Listening!
@rstoya05
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