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Below is a feature summary you must know to use Spring’s MVC RESTful Web Services. This article will show the features available, but not discuss pros & cons, use-cases or sell you on the benefits of REST.

PUT & POST in Browser Based Clients

Browsers do not allow PUT & DELETE – In web.xml configure HiddenHttpMethodFilter & on the page add the following inside your form <input type="hidden" name="_method" value="PUT"/>, with form submit set to POST. If using the Spring <form:form> tag, the hidden field is created for you, use any of the standard 7 HTTP verbs as desired.

Receiving Values in the URL Path, the RESTful Way

@PathVariable in Controller methods to extract values from the path.

You Rarely Need to Write Custom Parsers

<mvc:annotation-driven/> – automatically registers several marshallers simply with presence of corresponding jar in classpath

Configure – Don’t Code

Automatic Marshalling & Unmarshalling of XML, JSON, ATOM/RSS data
Controller annotations: @RequestBody & @ResponseBody
Example of JAXB2 Configuration in my OXM blog post named http://gordondickens.com/wordpress/2011/02/07/sending-beans-as-xml-with-jmstemplate/

Sending HTTP Response Codes to Clients

Success response status with @ResponseStatus controller method annotation.
Exception handling with @ExceptionHandler annotation on controller methods OR custom classes, also with annotated @ResponseStatus.
Note: @ResponseStatus disables the default behavior of void controller methods automatically returning the view.

Content Negotiation

Accept Header in Browser Based Clients

The HTML Accept header is not a reliable option for browser based clients to request content type. See Content Negotiation below.

Managing Client Content Type Requests

The HTTP Accept header is the typical REST vehicle for receiving the client’s requested MIME content type (application/JSON, application/XML, etc.)

Content Negotiation – Flexible Config Options

Spring’s ContentNegotiatingViewResolver for configuring client request data format. Several methods beyond the standard “Accept” header which will not work if you have browser based clients (Accept header, url extension, parameter, Java Activation Framework). URL extension (referred to as file extension) allows a URL to be appended with a string which can be mapped to a MIME type.

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

The same shortcut keys can be used in a parameter where URL can have “?format=json”. For JAF, the jar contains a /lib/mime.types file with mapped types already defined.

Client Side with RestTemplate

Spring’s RestTemplate is for client side development. In the Spring Template style, simply, set the URL, invoke the method & process the results. The main extension points in Spring Templates are done through Callbacks.

RestTemplate Callbacks

REST Improvements in Spring 3.1

Customizable @MVC

• Custom @ExceptionHandler support for @Controller methods
• Custom @ExceptionHandler support for @RequestBody & @ResponseBody
• You can write a BeanPostProcessor to change AnnotationMethodHandlerAdapter after construction
• Auto-detection of custom HttpMessageConverters – for example custom MyMappingJacksonHttpMessageConverter
• Support for custom message codes resolver with <mvc:annotation-driven/>

<mvc:annotation-driven>
    <mvc:custom-web-argument-resolvers>
        <bean class="org.example.MyWebArgumentResolver"/>
    </mvc:custom-web-argument-resolvers>
</mvc:annotation-driven>

<mvc:annotation-driven>
    <mvc:message-converters>
        <bean class="org.springframework.http.converter.StringHttpMessageConverter"/>
        <bean class="org.springframework.http.converter.ResourceHttpMessageConverter"/>
        <bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter"/>
    </mvc:message-converters>
</mvc:annotation-driven>

<mvc:annotation-driven message-codes-resolver="org.example.MyMessageCodesResolver"/>

REST Enhancements

• Interceptors for RestTemplate
• ClientHttpRequestInterceptor – ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution)
• bufferRequestBody property to the SimpleClientHttpRequestFactory to handle large payloads with RestTemplate
• New WebRequest.checkNotModified(String) // only had long support previously
• New @ResponseEntity
• To support OAuth with ClientHttpRequestInterceptors

Other REST Concepts

HATEOAS

Hypermedia as the Engine of Application State

• Wikipedia Article
• Craig McClanahan’s Why HATEOAS Article
• RESTful Web Flows – DZone Article

WADL

Web Application Description Language

• Wikipedia Article
• Learn WADL
• Do we need WADL?

Summary

Spring MVC REST helps us with:

• The power of <mvc:annotation-driven/> provides us the automatic marshalling/unmarshalling of content in REST
• The configuration flexibility of ContentNegotiatingViewResolver for our browser based clients

Want to Learn More?

Learn more about Spring REST by attending a Spring Training class at Chariot, or contact us for onsite training.

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