Chapter 12. Declarative Hyperlinking

To use Declarative Linking you need to add jersey-jersey.ent module to your pom.xml file:

<dependency>
    <groupId>org.glassfish.jersey.ext</groupId>
    <artifactId>jersey-declarative-linking</artifactId>
    <version>2.13</version>
</dependency>

If you're not using Maven make sure to have all needed dependencies (see jersey-declarative-linking) on the classpath.

Links are added to representations using the @InjectLink annotation on entity class fields. The Jersey runtime is responsible for injecting the appropriate URI into the field prior to serialization by a message body writer. E.g. consider the following resource and entity classes:

@Path("widgets")
public class WidgetsResource {
    @GET
    public Widgets get() {
        return new Widgets();
    }
}

public class Widgets {
    @InjectLink(resource=WidgetsResource.class)
    URI u;
}

After a call toWidgetsResource#get, the Jersey runtime will inject the value "/context/widgets" ^[1] into the returned Widgets instance. If an absolute URI is desired instead of an absolute path then the annotation can be changed to @InjectLink(resource=WidgetsResource.class, style=ABSOLUTE).

The above usage works nicely when there's already a URI template on a class that you want to reuse. If there's no such template available then you can use a literal value instead of a reference. E.g. the following is equivalent to the earlier example: @InjectLink(value="widgets", style=ABSOLUTE).

Referenced or literal templates may contain parameters. Two forms of parameters are supported:

Parameter values can be extracted from three implicit beans:

By default URI template parameter values are extracted from the implicit instance bean, i.e. the following two annotations are equivalent:

@InjectLink("widgets/{id}")

@InjectLink("widgets/${instance.id}")

The source for URI template parameter values can be changed using the @Binding annotation, E.g. the following three annotations are equivalent:

@InjectLink(value="widgets/{id}", bindings={
    @Binding(name="id" value="${resource.id}"}
)

@InjectLink(value="widgets/{value}", bindings={
    @Binding("${resource.id}")})
@InjectLink("widgets/${resource.id}")

Link value injection can be made conditional by use of the condition property. The value of this property is a boolean EL expression and a link will only be injected if the condition expression evaluates to true. E.g.:

@InjectLink(value="widgets/${instance.id}/offers",
    condition="${instance.offers}")
URI offers;

In the above, a URI will only be injected into the offers field if the offers property of the instance is true.

You can inject multiple links into an array of a List collection type. E.g.:

@InjectLinks({@InjectLink(resource=WidgetsResource.class, rel = "self")})
List<Link> links

HTTP Link headers can also be added to responses using annotations. Instead of annotating the fields of an entity class with @InjectLink, you instead annotate the entity class itself with @InjectLinks. E.g.:

@InjectLinks(
    value=@InjectLink("widgets/${resource.nextId}"),
    rel="next"
)

The above would insert a HTTP Link header into any response whose entity was thus annotated. The @InjectLink annotation contains properties that map to the parameters of the HTTP Link header. The above specifies the link relation as next. All properties of the @InjectLink annotation may be used as described above.

Multiple link headers can be added by use of the @InjectLinks annotation which can contain multiple @InjectLink annotations.

In order to add the Declarative Linking feature register DeclarativeLinkingFeature

// Create JAX-RS application.
final Application application = new ResourceConfig()
        .packages("org.glassfish.jersey.examples.linking")
        .register(DeclarativeLinkingFeature.class);