Declarative Hyperlinking Enhancements

I've spent some time fleshing out the code in the experimental declarative hyperlinking module I blogged about earlier. In that earlier entry I showed how you could use the new @Link annotation with existing URI templates either explicitly like this:

@Link("widgets/{id}")
URI link;

or by referencing a resource class @Path annotation value like this:

@Link(resource=WidgetResource.class)
URI link;

Expression Language Support

With the latest trunk code you can now use EL in explicit @Link templates, thanks to Ed Burns for helping to get me bootstrapped with the EL APIs. E.g.:

@Link("widgets/${instance.id}")
URI link;

The above would extract the value of the id property of the instance bean. Three beans are currently supported:

instance

The object whose class contains the @Link annotation currently being processed.

entity

The response entity object returned by the resource class method.

resource

The resource class instance that returned the entity.

Its straightforward to add others but these seemed like a useful set to start with.

Custom Bindings

By default, a URI template parameter is replaced by the value of a same-named property in the current instance. The following two annotations are therefore equivalent:

@Link("{id}")
@Link("${instance.id}")

Custom bindings allow the source of the value of a URI template parameter to be changed, e.g.:

@Link(value="{id}", bindings={
  @Binding(name="id", value="${resource.widgetId}")
})

In the above the {id} template parameter will be replaced with the value of the widgetId property of the resource class instance that returned the response. The name property of an @Binding gives the name of a URI template parameter, the value is an EL expression that defines how to get the value of the parameter.