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What's New in Spring MVC 3.2

Rossen Stoyanchev

VMware

presentation source

https://github.com/rstoyanchev/spring-mvc-32-update

Quick Recap and Timeline

Spring 3.0 / Dec 2009

Comprehensive REST support
Evolved @MVC programming model
Type conversion sub-system
MVC namespace

Spring 3.1 / Dec 2011

Point release
Nothing too significantly different or new
Straight-forward refinements of the Spring 3 model
Still, plenty of new features...

Spring 3.1 Recap

MVC Java config and Servlet 3 web container initialization
Revised @MVC infrastructure
@RequestMapping(consumes="", produces="")
Redirect and flash attributes
URI vars (data binding, redirect URLs, rendering)
UriComponentsBuilder
@RequestPart and Servlet 3 mulitpart requests

Spring 3.2 / Dec 2012

Servlet 3 async support
Error reporting in REST scenarios
Content negotiation strategies
Matrix variables
Spring MVC Test Framework
and more

Servlet 3 Async Support

HTTP Request-Response Semantics

Client makes a request
Server handles it and responds

Ajax Requests

Obtain new data without reloading entire page
Pages appear more dynamic and live
Still the same request-response semantics

Varying Degrees of "Live"-ness

Sometimes okay for client to poll every few minutes
Mail, Twitter, even "breaking" news
In other cases, it's just not real-time enough
Chat, collaboration, trading/finance

Long Polling

Client sends request and waits...
Server holds and doesn't respond until new data arrives
Client sends request and waits...
Server holds and doesn't respond until new data arrives
and so on

Long Polling Effect

Simulates server-side push
In most cases more effective than polling while using identical HTTP request-response semantics
However requests remain open for much longer

Servlet Containers

Traditionally thread-per-request
Long polling would quickly exhaust container threads
Hence the need for Servlet 3 async support

Servlet Thread Model

  [Servlet Thread]
      Start processing
      Do some work 
      Send response

Servlet 3 Async Thread Model

  [Servlet Thread]
      Start processing
      Switch to async mode
      Exit thread leaving response open








  .

Servlet 3 Async Thread Model

  [Servlet Thread]
      Start processing
      Switch to async mode
      Exit thread leaving response open

  [Application Thread]
      Produce or receive result
      Dispatch to container to resume processing




  .

Servlet 3 Async Thread Model

  [Servlet Thread]
      Start processing
      Switch to async mode
      Exit thread leaving response open

  [Application Thread]
      Produce or receive result
      Dispatch to container to resume processing

  [Servlet Thread]
      Start processing
      Process result from application thread
      Send response

Why Not Send Response From Application Thread?

We tried that in milestone 1
HttpServletRequest not usable in non-container thread
Cannot forward (e.g. no JSP rendering) or rely on various other request properties
Response should really be finalized within container

Servlet 3 Async Support
in Spring MVC

`@RequestMapping` return values

java.util.concurrent.Callable
DeferredResult
AsyncTask

java.util.concurrent.Callable

Produce value from @RequestMapping asynchronously
In thread managed by Spring MVC
Long-running DB job, 3rd party REST API call, ...

DeferredResult

Produce value from @RequestMapping asynchronously
In thread managed outside Spring MVC
JMS or AMQP listener, another HTTP request

AsyncTask

Same as returning Callable with extras
Override timeout value for async processing
Select specific AsyncTaskExecutor

Demo

Async request execution and log output

Spring MVC Showcase

Exceptions From `Callable`

Saved and handled after the dispatch
Through the HandlerExceptionResolver mechanism
Like any exception from @RequestMapping methods

Exceptions with `DeferredResult`

DeferredResult provides setErrorResult(Object)
Set an Exception or some alternative error value
Exception handled after the dispatch
Through the HandlerExceptionResolver mechanism

Servlet Filters

Must have the async-supported flag in web.xml
Can be executed from more than one thread
OncePerRequestFilter (+ all Spring MVC filters)
have been updated

Handler Interception

AsyncHandlerInterceptor
Intercept handler execution in container threads
afterConcurrentHandlingStarted vs postProcess/afterCompletion

Configuring Async Support

MVC Java Config
WebMvcConfigurer.configureAsyncSupport
MVC namespace
async-support sub-element of annotation-driven

What Can Be Configured?

Async timeout value (milliseconds)
AsyncTaskExecutor for Callable processing

`web.xml` Configuration

async-supported flag on all Filters and Servlet
dispatcher-type of ASYNC for Filters
Can be a bit repetitive

`WebApplicationInitializer`

Abstract Class Hierarchy

Servlet 3+ Java-based, container initialization
Registers a DispatcherServlet
Takes care of boilerplate
Sets async-supported flag and dispatcher-type

public class DispatcherServletInitializer extends
      AbstractAnnotationConfigDispatcherServletInitializer {

  protected Class<?>[] getRootConfigClasses() {
    return new Class<?>[] { RootConfig.class };
  }

  protected Class<?>[] getServletConfigClasses() {
      return new Class<?>[] { WebMvcConfig.class };
  }

  protected String[] getServletMappings() {
      return new String[] { "/" };
  }

  protected Filter[] getServletFilters() {
      return new Filter[] { new OpenSessionInViewFilter() };
  }

}

References

Async tab in Spring MVC Showcase

Chat Sample

Spring AMQP Stocks

Blog series

Error reporting in REST scenarios

Traditional Web vs REST API

In traditional, easy to present an error page
In REST API more varied responses
Communicate with status codes
Commonly write helpful details to response body

What Is Needed?

Application-specific, application-wide strategy to write details to the response body
Including standard (internal) Spring MVC exceptions
Global @ExceptionHandler
Some alternative to DefaultHandlerExceptionResovler

Global `@ExceptionHandler` Methods

@ControllerAdvice - component annotation
Add @ExceptionHandler methods
Nothing else to configure

Other Uses Cases for `@ControllerAdvice`

@InitBinder methods
Global DataBinder initialization
@ModelAttribute methods
Global "pre" handling

`ResponseEntityExceptionHandler`

Alternative to DefaultHandlerExceptionResolver
Protected methods for each exception return ResponseEntity<Object>
Makes it easy to write error details to the response body

Servlet Container Error Page

HTML formatted error page
For response status codes 4xx and 5xx
Or with response.sendError(int, String)

Custom Error Page (Servlet 3+)

error-page in web.xml
Don't map to exception type or status
Location only (JSP page, even controller URL)
Status and message available in request attributes "javax.servlet.error.status_code" "javax.servlet.error.message"

References

See updated section on Exception Handling in reference docs

Global exception in Spring MVC Showcase

Content Negotiation Strategies

Prior to Spring 3.2

@ResponseBody used 'Accept' header
@RequestMapping(produces="") did likewise
While ContentNegotiatingViewResolver ...
offered many additional options

`ContentNegotiationStrategy`

(Spring 3.2)

By 'Accept' Header
By URL extension (.xml, .json, etc)
By Request parameter, i.e. /accounts/1?format=json
Fixed content type, i.e. a fallback option

`ContentNeogitationManager`

Configured with one or more instances of ContentNegotiationStrategy
Plugged into various places
RequestMappingHandlerMapping RequestMappingHandlerAdapter ExceptionHandlerExceptionResolver
ContentNegotiatingViewResolver

Default Settings

(without MVC Java Config & Namespace)

'Accept' header only
Matches existing defaults for @ResponseBody

MVC Java Config & Namespace

Path extension 1st, 'Accept' header 2nd
.json, .xml auto-registered if libraries present
Matches defaults of ContentNegotiatingViewResolver

References

See section on Configuring Content Negotiation in reference docs

URL extension for content negotiation in Spring MVC Showcase

Matrix Variables

What Are They?

Originally mentioned in Tim Berners-Lee post
The term is not used in RFC URI spec
However it is most commonly used

"Each path segment may include a sequence of parameters, indicated by the semicolon ";" character. The parameters are not significant to the parsing of relativeb references."

RFC 2396, section 3.3

"The semicolon (";") and equals ("=") reserved characters are often used to delimit parameters and parameter values applicable to that segment. The comma (",") reserved character is often used for similar purposes."

RFC 3986, section 3.3

Two Types of Usage

As path segment name-value pairs
JFrog API
/qa-releases;buildNumber=135;revision=3.2
As delimited list path segment
StackExchange API
/answers/id1;id2;id3;id4/comments

How To Use In Spring MVC

If you expect ";" content in a path segment
Represent the path segment with a URI variable
Declare one or more @MatrixVariable args

The Common Case

// GET /pets/42;q=11;r=22

@RequestMapping(value = "/pets/{petId}")
public void findPet(
    @PathVariable String petId, @MatrixVariable int q) {

  // petId == 42
  // q == 11

}

Obtain All Matrix Variables

// GET /owners/42;q=11;r=12/pets/21;q=22;s=23

@RequestMapping(value = "/owners/{ownerId}/pets/{petId}")
public void findPet(
    @MatrixVariable Map<String, String> matrixVars) {

    // matrixVars: ["q" : [11,22], "r" : 12, "s" : 23]

}

Qualify Path Segment

// GET /owners/42;q=11/pets/21;q=22

@RequestMapping(value = "/owners/{ownerId}/pets/{petId}")
public void findPet(
    @MatrixVariable(value="q", pathVar="ownerId") int q1,
    @MatrixVariable(value="q", pathVar="petId") int q2) {    

  // q1 == 11
  // q2 == 22

}

References

Section on Matrix Variables in reference docs

Spring MVC Test Framework

`MockHttpServletRequest/Response`

Stub implementations
spring-test module
Very commonly used in controller unit tests

Better Controller Unit Tests

Take existing controller unit tests
Invoke controllers through DispatcherServlet
Using fluent API
Based on actual Spring MVC configuration
Without a Servlet container

Example


mockMvc.perform(get("/foo").accept("application/json"))
  .andExpect(status().isOk())
  .andExpect(content().mimeType("application/json"))
  .andExpect(jsonPath("$.name").value("Lee"));

Tests in Spring MVC Showcase

Client and Server sample tests in the Spring Framework

Testing Web Applications with Spring 3.2

(Thursday 10:15)

Other Improvements

`GenericHttpMessageConverter`

Read HttpInputMessage to generic target type
Supported with Jackson JSON library
Also Jaxb2CollectionHttpMessageConverter

`RestTemplate`

Response with Generic Type



ParameterizedTypeReference<List<Integer>> listOfInts =
    new ParameterizedTypeReference<List<Integer>>() {};


ResponseEntity<List<Integer>> result =
    restTemplate.exchange(
        "http://example.com/accounts",
        HttpMethod.GET, null, listOfInts);

`@RequestBody`

Generic Method Argument


@RequestMapping
public void handle(@RequestBody List<Integer> ints) {

}

HTTP PATCH method

Jackson JSON 2

`JacksonObjectMapperFactoryBean`

Next?

WebSocket support
Servlet 3.1
Externalized request mappings
Declarative caching

Questions?

Thank You!

Twitter

@rstoya05

What's New in Spring MVC 3.2

Rossen Stoyanchev

VMware

presentation source

https://github.com/rstoyanchev/spring-mvc-32-update

Quick Recap and Timeline

Spring 3.0 / Dec 2009

Spring 3.1 / Dec 2011

Spring 3.1 Recap

Spring 3.2 / Dec 2012

Servlet 3 Async Support

HTTP Request-Response Semantics

Ajax Requests

Varying Degrees of "Live"-ness

Long Polling

Long Polling Effect

Servlet Containers

Servlet Thread Model

Servlet 3 Async Thread Model

Servlet 3 Async Thread Model

Servlet 3 Async Thread Model

Why Not Send Response From Application Thread?

Servlet 3 Async Support in Spring MVC

@RequestMapping return values

java.util.concurrent.Callable

DeferredResult

AsyncTask

Demo

Async request execution and log output

Exceptions From Callable

Exceptions with DeferredResult

Servlet Filters

Handler Interception

Configuring Async Support

What Can Be Configured?

web.xml Configuration

WebApplicationInitializer

Abstract Class Hierarchy

References

Error reporting in REST scenarios

Traditional Web vs REST API

What Is Needed?

Global @ExceptionHandler Methods

Other Uses Cases for @ControllerAdvice

ResponseEntityExceptionHandler

Servlet Container Error Page

Custom Error Page (Servlet 3+)

References

Content Negotiation Strategies

Prior to Spring 3.2

ContentNegotiationStrategy

(Spring 3.2)

ContentNeogitationManager

Default Settings

(without MVC Java Config & Namespace)

MVC Java Config & Namespace

References

Matrix Variables

What Are They?

"Each path segment may include a sequence of parameters, indicated by the semicolon ";" character. The parameters are not significant to the parsing of relativeb references."

"The semicolon (";") and equals ("=") reserved characters are often used to delimit parameters and parameter values applicable to that segment. The comma (",") reserved character is often used for similar purposes."

Two Types of Usage

How To Use In Spring MVC

The Common Case

Obtain All Matrix Variables

Qualify Path Segment

References

Spring MVC Test Framework

MockHttpServletRequest/Response

Better Controller Unit Tests

Example

Other Improvements

GenericHttpMessageConverter

RestTemplate

Response with Generic Type

@RequestBody

Generic Method Argument

HTTP PATCH method

Jackson JSON 2

JacksonObjectMapperFactoryBean

Servlet 3 Async Support
in Spring MVC

`@RequestMapping` return values

Exceptions From `Callable`

Exceptions with `DeferredResult`

`web.xml` Configuration

`WebApplicationInitializer`

Global `@ExceptionHandler` Methods

Other Uses Cases for `@ControllerAdvice`

`ResponseEntityExceptionHandler`

`ContentNegotiationStrategy`

`ContentNeogitationManager`

`MockHttpServletRequest/Response`

`GenericHttpMessageConverter`

`RestTemplate`

`@RequestBody`

`JacksonObjectMapperFactoryBean`