Building Web

Applications with
Spring 3.0
by Bob McCune
www.bobmccune.com

Monday, May 18, 2009 1

 Agenda
Spring MVC Overview
Spring MVC Infrastructure
Developing Controllers
RESTful Web Services
Demo

Monday, May 18, 2009 2

 Spring MVC
Overview

Monday, May 18, 2009 3

 What is MVC?
Model
Domain-specific data and processing logic
Entities, services, repositories, etc.
View
User-facing presentation
JSPs, Velocity/Freemarker Templates, XSLT, etc.
Controller
Mediator between model and view
Responsible for routing requests and responses

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 What is Spring MVC?
Core web component of the Spring Framework
Foundation of Spring’s web strategy
Similar to Struts but with improvements:
Better separation of concerns
Robust data binding and validation
Customizable type coercion with property editors
Supports wide variety of view technologies:
JSP/JSTL, XML/XSLT, Freemarker, Velocity, PDF, etc.
Significantly enhanced in 2.5 release and further refined in 3.0

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 Spring MVC
Basics

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 Request/Response Handling
2
Handler Mapping
Request

Controller

1 3
Request Request
DispatcherServlet Controller
Response ModelAndView

Response Model View Name

4
View
View Resolver
5
View

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 DispatcherServlet
Front Controller implementation in Spring MVC
Handles incoming request and dispatches to appropriate handler
Coordinates communication between infrastructural
components
Wired as standard servlet in web.xml
Upon initialization looks for servletname-servlet.xml
Default values defined in DispatcherServlet.properties
Overriding defaults replaces default values!

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 Configuring web.xml
Servlet Configuration
<servlet>
<servlet-name>spring</servlet-name>
<servlet-class>
org.springframework.web.servlet.DispatcherServlet
</servlet-class>
<load-on-startup>1</load-on-startup> DispatcherServlet
</servlet> finds context
configuration
Servlet Mapping based on name
<servlet-mapping>
<servlet-name>spring</servlet-name>
<url-pattern>/v3/*</url-pattern>
</servlet-mapping>

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 HandlerMapping
Defines interface to select appropriate handler (Controller)
DispatcherServlet consults HandlerMapping collection to locate
appropriate controller
Interceptors can be applied to customize pre/post processing
Common implementations:
BeanNameUrlHandlerMapping: Maps requests based on bean names
SimpleUrlHandlerMapping: Maps request URLs to Controller beans
ControllerClassNameHandlerMapping: Auto generates mappings by class name
DefaultAnnotationHandlerMapping: Maps request based on annotations

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 Controller
Controller defines the interface to handle and process requests.
Provides access to the HttpServletRequest and HttpServletResponse
Returns ModelAndView
Composite data holder for the data model and a view
Model is typically a Map variant
View can be logical view name or actual View instance
public ModelAndView handleRequest(HttpServletRequest request,
HttpServletResponse response) throws Exception {

// Forward request to “artists list” view

return new ModelAndView(“artists”);
}

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 ViewResolver
ViewResolver defines the interface to select an appropriate View for the
response
ViewResolver instances can be chained together into an ordered
collection
Common implementations include:
InternalResourceViewResolver

ResourceBundleViewResolver

XmlViewResolver

<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>

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 View
Defines the interface for objects rendering a client response
Iterates through the values in the model to generate response
Framework provides a wide variety of View choices:
Common Web View:
JstlView, FreemarkerView,VelocityView, XsltView
Special Format View:
AbsractExcelView, AbstractPdfView, JasperReportsView
New Views in Spring 3.0: New in 3.0

MarshallingView, AbstractAtomFeedView, AbstractRssFeedView

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 spring-servlet.xml
<beans>
<bean id="handlerMapping"
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">
<props>
<prop key="/v3/genres.html">genreController</prop>
<prop key="/v3/artists.html">artistController</prop>
</props>
</property>
</bean>

<bean id="artistController" class="com.mccuneos.spring.web.controller.ArtistController"/>

<bean id="genreController" class="com.mccuneos.spring.web.controller.GenreController"/>

<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
<beans>

Monday, May 18, 2009 14

 spring-servlet.xml
<beans>
<bean id="handlerMapping"
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">
<props>
<prop key="/v3/genres.html">genreController</prop>
<prop key="/v3/artists.html">artistController</prop>
</props>
</property>
</bean>

<bean id="genreController" class="com.mccuneos.spring.web.controller.ArtistController"/>

<bean id="artistsController" class="com.mccuneos.spring.web.controller.GenreController"/>

<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
<beans>

Monday, May 18, 2009 15

 spring-servlet.xml
<beans>
<bean id="handlerMapping"
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">
<props>
<prop key="/v3/genres.html">genreController</prop>
<prop key="/v3/artists.html">artistController</prop>
</props>
</property>
</bean>

<bean id="genreController" class="com.mccuneos.spring.web.controller.ArtistController"/>

<bean id="artistsController" class="com.mccuneos.spring.web.controller.GenreController"/>

<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
<beans>

Monday, May 18, 2009 16

 spring-servlet.xml
<beans>
<bean id="handlerMapping"
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="mappings">
<props>
<prop key="/v3/genres.html">genreController</prop>
<prop key="/v3/artists.html">artistController</prop>
</props>
</property>
</bean>

<bean id="genreController" class="com.mccuneos.spring.web.controller.ArtistController"/>

<bean id="artistsController" class="com.mccuneos.spring.web.controller.GenreController"/>

<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/jsp/"/>
<property name="suffix" value=".jsp"/>
</bean>
<beans>

Monday, May 18, 2009 17

 Developing
Spring MVC
Controllers

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 Controller
Controllers historically built on Controller interface
Specialized implementations included:
Simple Form Controllers
Form processing lifecycle
Databinding and validation
Wizard Form Controllers
Multi-page navigation
Multi-action Controllers
Grouped related, stateless operations

Monday, May 18, 2009 19

 Controller Hierarchy

d
Controller

e
AbstractController

c a t e
D ep r
MultiActionController AbstractUrlViewController BaseCommandController

AbstractCommandController

AbstractFormController

SimpleFormController

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 Controller to @Controller
Designates a class as a Spring MVC Controller
Removes the need to implement or extend Spring-specific classes
@Controller stereotype automatically be picked up if using
component scanning
<context:component-scan base-package="com.company.spring.web" />

Flexible method signatures

No need to implement/override lifecycle methods
Can eliminate dependencies on Servlet API
No need to “mock out” dependencies in unit tests

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 Flexible Method Arguments
Method signatures are very flexible
Arguments can be:
Servlet types: HttpServletRequest, HttpServletResponse,
HttpSession
WebRequest: wrapper over Servlet specifics
I/O types: InputStream, OutputStream, Reader, Writer
Model types: Model, ModelMap, Map
Model attributes, Request parameters
Locale

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 Flexible Return Types
ModelAndView: Wraps model and View or logical view
name
Model or Map: Return model with view implicitly defined
Will use RequestToViewNameTranslator
View: View instance to be used to render response
String: Interpreted as logical view name
void: Can return void if Controller handles response
Any object: Will be used as single model value

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 @RequestMapping
Used to map URL patterns to controllers
Can be applied at either a class and/or method level
Multi-action controllers commonly defined at method level
Form controllers applied at class level with method level
annotations used to narrow request to particular type
Greater mapping flexibility than previous releases

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 @RequestParam
Used to bind request parameters to method parameters
Limits or removes needs to rely on Servlet API
@RequestParam designates a required parameter
Can be made optional with required=false
@Controller
@RequestMapping("/edit.do")
public class EditController {

@RequestMapping(method = RequestMethod.GET)
public String configure( @RequestParam("id") int id, ModelMap model) {
model.put(service.getContact(id));
return “edit”;
}
}

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 @ModelAttribute/
@SessionAttribute
Used to map model data into controller
Used at a method level to maps model attribute to method
argument
No need to work directly with HttpServletRequest
Can also be used at method level to provide reference data
@ModelAttribute is processed before @RequestMappings so
data is pre-populated before controller processing
Can use @SessionAttribute to store and retrieve session data

Monday, May 18, 2009 26

 @InitBinder and
WebBindingInitializer
Spring’s data binding capabilities are one of the more compelling
reasons to use Spring MVC
Built in support for all primitive/wrapper types
Uses standard Java SE PropertyEditor instances for type coercion.
Can write custom editors for advanced binding.
Custom editors can be mapped:
Controller using the @InitBinder annotation
Application level use implementation of WebBindingInitializer
New type conversion SPI and converter API New in 3.0

Provides Java 5 friendly data type converter strategy

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 Convention /
Configuration
ControllerClassNameHandlerMapping
Automatically generates mapping based on Controller name
Removes “Controller” from name and lowercases resulting value
E.g. ArtistController maps to /artist*

Model and ModelMap

Generates attribute names from model types
Artist produces “artist” attribute
List<Artist> produces “artistList” attribute

RequestToViewNameTranslator
Generates logical view name from incoming request
E.g. Request for http:/server/artists.html produces logical view name of “artists”

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 REST Support

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 What is REST?
REpresentational State Transfer
Lightweight, resource-oriented architectural style
Unlike SOAP or XML-RPC, is not a standard
Stateless, cacheable, scalable communication protocol
Uses standard HTTP methods to read and write data
Provides uniform interface for interacting with resources
Nouns used to represent resources: artists, albums, etc.
Verbs defined through standard HTTP methods

Monday, May 18, 2009 30

 HTTP Methods
Resource interaction through standard HTTP methods
GET: Gets a representation of resource. Safe operation.
POST: Creates or updates resource.
PUT: Creates or updates resource. Idempotent.
DELETE: Deletes a resource. Idempotent.
HEAD: GET request without body. Returns headers only.
OPTIONS: Discovery method to determine allows.

Monday, May 18, 2009 31

 Spring 3.0 REST Support
Builds on Spring 2.5’s @Controller Model
Focuses on making it simple to expose and consume RESTful Web
Services
Client-side access greatly simplified via RestTemplate
Server-side development enhanced with expanded request mappings
and path variables
Provides competing approach to JAX-RS implementations:
Jersey
RESTEasy
Restlet

Monday, May 18, 2009 32

 URI Templates
RESTful services define resource locations through URIs
http://www.host.com/orders/{orderId}
Variable expansion would convert URI to:
http://www.host.com/orders/8675309
Spring MVC implements URI Templates through its standard
@RequestMapping annotation
@PathVariable annotation can extract template values
from template variables

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 Mapping Requests
Uses standard Spring MVC @RequestMapping annotation
Supports URI templates in path expressions
@Controller
@RequestMapping("/artists/{artistId}")
public class ArtistController {

@RequestMapping(method = RequestMethod.POST)
public String create(Artist artist) { return "artist"; }

@RequestMapping(method = RequestMethod.DELETE)
public String delete(Long id) { return "artist"; }
}

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 @PathVariable
@PathVariable maps URI template placeholders to argument
values
Can use multiple @PathVariable annotations
Values can be explicitly defined or inferred through debug info
@Controller
public class AlbumController {

@RequestMapping(value = "/artists/{artistId}/albums/{albumId}"
method = RequestMethod.GET)
public Album getAlbum(@PathVariable("artistId") Long artistId,
@PathVariable("albumId") Long albumId) {

return service.findAlbum(artistId, albumId);
}
}

Monday, May 18, 2009 35

 3.0 Controller Annotations
@RequestHeader
Allows request headers to be bound to method arguments
@CookieValue
Allows cookie values to be bound to method arguments
@RequestBody
Allows binding request body to a method argument
Request body converted using HttpMethodConverter implementations
Implementations provided for converting byte arrays, strings, form
values, XML sources, and JSON (forthcoming)

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 3.0 Views
Feed Views based on ROME project:
AbstractRssFeedView: renders an RSS feed
AbstractAtomFeedView: renders an ATOM feed
MarshallingView: returns XML representation using Spring’s
OXM framework
JacksonJsonView: renders a response in JSON format
Currently only available in Spring JS project
Hopefully moved to core in final release

Monday, May 18, 2009 37

 3.0 JSP Tags
Spring MVC JSP tags have been expanded to support REST
<form:form> tag enhanced to support all HTTP methods
Browsers only support sending GET and POST requests
HiddenHttpMethodFilter converts specified method to hidden
form field
<spring:url> tag enhanced to support URI templates

Monday, May 18, 2009 38

 Content Negotiation
A key feature of REST is the ability to return multiple
representations of a resource
XML, HTML, Text, JSON, etc.
Two strategies for client to request content type:
Specify the resource’s file extension
Set the appropriate Accept Header
Spring provides a ContentNegotiationViewResolver
Allows mapping mime types to views

Monday, May 18, 2009 39

 ETag Caching
ETags (entity tags) are a response header sent to determine if
resource has changed
Unchanged content will return 304: Not Modified header
Spring supports shallow ETag caching with ShallowEtagHeaderFilter
Standard javax.servlet.Filter
Doesn’t save processing, but does reduce bandwidth
Generates MD5 Hash for rendered view
Subsequent requests use this value in If-None-Match to compare if
response should be resent

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 RestTemplate
Provides simplified client access to REST services
Interacting with resources often a single line of code
Conceptually similar to other Spring templates:
JdbcTemplate
JmsTemplate
Provides callback methods to customize response handling
Uses ClientHttpRequest object based on java.net.URLConnection
and Jakarata Commons
Configurable with HttpMessageConverters

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 RestTemplate Methods
HTTP Method RestTemplate Method
getForObject(String url, Class<T> responseType,
GET String... urlVariables)

postForLocation(String url, Object request,

POST String... urlVariables)

PUT put(String url, Object request, String... urlVariables)

DELETE delete(String url, String... urlVariables)

OPTIONS optionsForAllow(String url, String... urlVariables)

HEAD headForHeaders(String url, String… urlVariables)

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 RestTemplate Example
Source
RestTemplate template = new RestTemplate();

String URI = "http://localhost:8080/springmvc/v3/genres.xml";

Source source = template.getForObject(URI, Source.class);

TransformerFactory factory = TransformerFactory.newInstance();

Transformer transformer = factory.newTransformer();
transformer.transform(source, new StreamResult(System.out));

Produces
<list>
<Genre>
<id>1</id><name>Rock</name>
<id>2</id><name>Jazz</name>
<id>3</id><name>Country</name>
</Genre>
</list>

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 Demo

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 Summary
Spring MVC is a simple, yet powerful Model 2 web framework
@Controllers provide more flexibility that Controller hierarchy
Broad range of argument values
Any object type can be returned from controller method
@RequestMappings enhanced to support RESTful services
URI Template variables extracted using @PathVariable
New annotations provided to meet needs of REST developers
RestTemplate greatly simplifies client access to REST services

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