Spring Mvc Rest

Building RESTful
applications with
Spring MVC

Craig Walls

Who Am I?
Java, Spring, and OSGi fanatic
Principal Consultant with Improving
Author
XDoclet in Action (Manning)

Spring in Action (Manning)

Modular Java (Pragmatic Bookshelf)

E-mail: craig@habuma.com Blog: http://www.springinaction.com Twitter: @habuma Slides: http://www.slideshare.net/habuma

What REST is NOT!!!

Web Services
with URLs

E-mail: craig@habuma.com Blog: http://www.springinaction.com Twitter: habuma

It’s about Resources

Things, not actions

Requests, not demands

Resources, not services

Transfer of state, not RPC


The Pillars of REST

Resources

URIs/URLs

HTTP Methods

Representations


The Pillars of REST

Resources
Produced as model data in Spring MVC Controllers

URIs/URLs
Supported in handler methods by @PathParam

HTTP Methods
@RequestMapping, HiddenHttpMethodFilter, <form:form>

Representations
Rendered by view resolvers
HTML, XML, JSON, RSS, Atom, PDF, Excel, etc.
Negotiated by ContentNegotiatingViewResolver


Identifying Resources


Demanding URLs

Direct Imperative Resource identifier
Command is pushed into
a query parameter

http://www.somestore.com/displayProduct?sku=1234

Very service-y
Not very cacheable or
search engine friendly


Resourceful URLs

The focus is
on the product, We’re requesting
not the action a product’s info

http://www.somestore.com/product/1234

Cacheable This URL also
identifies a product
(within a context)


Spring MVC overview


DispatcherServlet

In /WEB-INF/web.xml
<servlet>
<servlet-name>spitter</servlet-name>
<servlet-class>
org.springframework.web.servlet.DispatcherServlet
</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>

<servlet-mapping>
<url-pattern>/app/*</url-pattern>
</servlet-mapping>


ContextLoaderListener
In /WEB-INF/web.xml
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
/WEB-INF/spitter-security.xml
classpath:service-context.xml
classpath:persistence-context.xml
classpath:dataSource-context.xml
classpath:setup-context.xml
</param-value>
</context-param>

<listener>
<listener-class>
org.springframework.web.context.ContextLoaderListener
</listener-class>
</listener>


UrlRewriteFilter
In /WEB-INF/web.xml
<filter>
<filter-name>UrlRewriteFilter</filter-name>
<filter-class>
org.tuckey.web.filters.urlrewrite.UrlRewriteFilter
</filter-class>
</filter>
<filter-mapping>
<filter-name>UrlRewriteFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

In /WEB-INF/urlrewrite.xml
<urlrewrite default-match-type="wildcard">
<rule>
1234
/pr oduct/ <from>/resources/**</from>
<to>/resources/$1</to>
/1234
</rule>
uct
/ap p/prod <rule>
<from>/**</from>
<to>/app/$1</to>
</rule>
<outbound-rule>
<from>/app/**</from>
<to>/$1</to>
</outbound-rule>
</urlrewrite>

Essential Configuration
Scan for controller (and other) components
<context:component-scan
base-package="com.habuma.sample.mvc" />

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

Handle annotation-driven request mappings
<mvc:annotation-driven/>


Use-case-based controllers
VERB!!!
@Controller
public class DisplayProductController {
@RequestMapping(value="/displayProduct.htm")
public String showProductBySku(String sku,
Map<String,Object> model) {
Product product = // ... lookup product ...
model.put("product", product);
return "product";
}
// ...
}

http://host/myApp/displayProduct.htm?sku=1234


Resource-oriented controller
Noun
@Controller Verb
@RequestMapping("/product")
public class ProductController {
@RequestMapping(value="/{sku}", method=GET)
public String showProductBySku(
@PathVariable String sku,
Map<String,Object> model) {
Product product = // ... lookup product ...
model.put("product", product);
return "product";
}
}
http://host/myApp/product/1234


HTTP Methods

GET, DELETE, PUT
Idempotent
Transfers state of resource
POST
Not Idempotent
Sends data (not nec. state)


PUT vs. POST

PUT
Used to transfer state to server
Useful when the resource’s URL is known
POST
Used to send data to server
Useful when the resource’s URL is unknown
or when transferring partial state


Handling DELETE

@Controller

...

@RequestMapping(value="/{sku}", method=DELETE)
public String deleteProduct(
@PathVariable String sku) {
// ... delete product ...
return "redirect:home";
}
}


Handling PUT
@Controller

...

@RequestMapping(value="/{sku}", method=PUT)
public String saveProduct(
@PathVariable String sku,
Product product) {
// ... save product ...
return "redirect:/product/" + sku;
}
}

Handling POST
@Controller

...

@RequestMapping(method=POST)
public String setPrice(String sku,
double price) {
// ... update price ...
return "redirect:/product/" + sku;
}
}
http://host/myApp/product
FORM DATA: sku=1234
price=5.99

Using PUT/DELETE in forms
Most browsers only support GET and POST
Spring’s <form:form> supports all
<form:form method="DELETE"
action="http://host/myApp/product/1234">
...
</form:form>

Hidden method ﬁeld
<form method="POST"
action="http://host/myApp/product/1234">
<input type="hidden" name="_method"
value="DELETE">
...
</form>

HiddenHttpMethodFilter
<filter>
<filter-name>httpMethodFilter</filter-name>
<filter-class>
org.springframework.web.filter.HiddenHttpMethodFilter
</filter-class>
</filter>

<filter-mapping>
<filter-name>httpMethodFilter</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>

HiddenHttpMethodFilter
POST
DELETE
_method=DELETE


Data representation

PDF RSS/Atom

Spring MVC
Views
JSON

Excel


Negotiating Content

Request

Content
Negotiating
View
Resolver


Choosing a view

1. Determine the media type
URL path extension/mediaTypes
format parameter
URL path extension/JAF
HTTP Accept header

2. Find a view resolver that
serves that media type


ContentNegotiatingViewResolver

<bean class="org.springframework.web.servlet.view.
ContentNegotiatingViewResolver">
<property name="mediaTypes">
<map>
<entry key="htm" value="text/html"/>
<entry key="json" value="application/json"/>
</map>
</property>
<property name="defaultViews">
<list>
<bean class="org.springframework.web.servlet.view.json.
MappingJacksonJsonView" />
</list>
</property>
</bean>

<bean id="spittles"
class="com.habuma.spitter.mvc.view.SpittlesAtomView"/>


Spring’s new views
MappingJacksonJsonView
MarshallingView
AbstractAtomFeedView
AbstractRssFeedView


XML Marshalling View

<bean id="oxmMarshaller"
class="org.springframework.oxm.xstream.XStreamMarshaller" />

<bean id="marshallingHttpMessageConverter"
class="org.springframework.http.converter.xml.
MarshallingHttpMessageConverter">
<property name="marshaller" ref="oxmMarshaller" />
<property name="unmarshaller" ref="oxmMarshaller" />
</bean>


Sample RSS View
public class SpittlesRssView extends AbstractRssFeedView {

@Override
protected List<Item> buildFeedItems(
Map<String, Object> model,
HttpServletRequest request,
HttpServletResponse response) throws Exception {

@SuppressWarnings("unchecked")
List<Spittle> spittles = (List<Spittle>) model.get("spittles");
List<Item> items = new ArrayList<Item>();
for (Spittle spittle : spittles) {
Item item = new Item();
item.setTitle(spittle.getText());
item.setPubDate(spittle.getWhen());
item.setAuthor(spittle.getSpitter().getFullName());
items.add(item);
}

return items;
}
}


Sample Atom View
public class SpittlesAtomView extends AbstractAtomFeedView {

@Override
protected List<Entry> buildFeedEntries(
Map<String, Object> model,
HttpServletRequest request,
HttpServletResponse response) throws Exception {

@SuppressWarnings("unchecked")
List<Spittle> spittles = (List<Spittle>) model.get("spittles");
List<Entry> entries = new ArrayList<Entry>();
for (Spittle spittle : spittles) {
Entry entry = new Entry();
entry.setTitle(spittle.getText());
entry.setCreated(spittle.getWhen());
entry.setAuthors(asList(spittle.getSpitter().getFullName()));
entries.add(entry);
}

return entries;
}
}


ETags
Returns HTTP 304 if content is unmodiﬁed
if-none-match
(MD5 Hash comparison)
Saves bandwidth

<filter>
<filter-name>etagFilter</filter-name>
<filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class>
</filter>

<filter-mapping>
<filter-name>etagFilter</filter-name>
</filter-mapping>


RestTemplate
In Spring context: (or yes, it could just be new’d up in Java)
<bean id="restTemplate"
class="org.springframework.web.client.RestTemplate">

In Java:
RestTemplate rest = (RestTemplate) context.getBean("restTemplate");
Map result = rest.getForObject(
"http://localhost:8080/mugbooks/book/1.json", Map.class);


Summary

• Spring provides a ﬂexible web MVC
framework

• Full support for REST as of Spring 3.0
• Can consume REST services via a template


Thank You

Don’t forget the evals!

Spring Mvc Rest

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