Spring extension - Configuration of Restlet resources

Configuration of basic properties

Restlet resources support only limited configuration beyond injecting custom dependencies such as the ObjectContainer in the example above. To make specific ServerResource classes more reusable, it would be helpful if their basic properties could be configured through Spring:

  • available
  • modifiable
  • negotiateContent
  • readable

Currently, the init method resets these properties to their default values but, in the Spring component life cycle, is invoked after Spring sets the properties. An obvious workaround is to refine the init method like so:

    @Override
    public void init(Context context, Request request, Response response) {
        final ResourcePropertyHolder backup = new ResourcePropertyHolder(); 
        BeanUtils.copyProperties(this, backup);
        super.init(context, request, response);
        BeanUtils.copyProperties(backup, this);
    }

Configuration of representation templates

In addition, it would be quite useful if one could map media types to representation templates in Spring. In the following example, we explore this idea further by mapping different media types to different Freemarker and JSON representation factories. Whenever a Resource creates a concrete representation, it passes a uniform data model to the representation factory, which then instantiates the template with the data model and returns the resulting representation. (The Freemarker configuration is also handled by Spring.)

<bean id="resource" class="helloworldrestlet.HelloWorldResource"
    scope="prototype">
    <property name="available" value="true" />
    <property name="representationTemplates">
        <map>
            <entry key-ref="org.restlet.data.MediaType.TEXT_PLAIN"
                value-ref="hwFreemarkerTextPlain" />
            <entry key-ref="org.restlet.data.MediaType.TEXT_HTML"
                value-ref="hwFreemarkerTextHtml" />
            <entry key-ref="org.restlet.data.MediaType.APPLICATION_JSON"
                value-ref="jsonRepresentationFactory" />
        </map>
    </property>
</bean>

<bean id="hwFreemarkerTextPlain"
    class="edu.luc.etl.restlet.spring.FreemarkerRepresentationFactory">
    <property name="templateName" value="hw-plain.ftl" />
    <property name="freemarkerConfig" ref="freemarkerConfig" />
</bean>

<bean id="hwFreemarkerTextHtml"
    class="edu.luc.etl.restlet.spring.FreemarkerRepresentationFactory">
    <property name="templateName" value="hw-html.ftl" />
    <property name="freemarkerConfig" ref="freemarkerConfig" />
</bean>

<bean id="jsonRepresentationFactory"
    class="edu.luc.etl.restlet.spring.JsonRepresentationFactory" />

<!-- omitted beans for specific MediaType static fields -->

<bean id="freemarkerConfig"
    class="freemarker.template.Configuration">
    <property name="directoryForTemplateLoading"
        value="src/test/resources/presentation" />
    <property name="objectWrapper">
        <bean class="freemarker.template.DefaultObjectWrapper" />
    </property>
</bean>

When using this approach, the ServerResources themselves become very simple, for example:

public class HelloWorldResource extends ConfigurableRestletResource {
    @Override
    public Representation get(Variant variant) {
    Map dataModel = Collections.singletonMap("DATE", (Object) new Date());
    return createTemplateRepresentation(variant.getMediaType(), dataModel);
    }
}

A working proof-of-concept for this approach is available through Git at https://github.com/LoyolaChicagoCode/configurableresource-restlet-java. Support for the missing configuration of representations tied to responses to non-GET requests is in the works.