halbuilder-jaxrs

This extension integrates the HalBuilder functionality with the JAX-RS API. It provides an easy way to marshal and unmarshal Java objects using JSON or XML HAL representations

It uses annotations similar to JAXB API to identify the properties, links and embedded elements of the Object to help consuming and producing HAL representations

Annotating Java objects

The following code show a basic yet complete example of using those annotations:

@HalRootElement
public class Resource {

    @HalProperty( name="id")
    private Long id;
    @HalProperty( name="name")
    private String name;
    @HalProperty( name="birthDate")
    private Date birthDate;
    @HalEmbedded("subresources")
    private List<SubResource> subresources;


    @HalSelfLink
    public String getSelfLink()
    {
        return "resources/" + id;
    }
    
    @HalLink( "subresources")
    public String getSubResourcesLink()
    {
        return getSelfLink() + "/subresources";
    }
    
    /* Constructors, getters and setters....*/
    ...
}

The available annotations are:

• @HalRootElement Denotes a object that can be read from or written to a HAL representation
• @HalProperty Denotes a object field that represents a HAL property
• @HalEmbedded Denotes a object field that represents a HAL embedded object
• @HalSelfLink Denotes a object method that generates the link to the resource
• @HalLink Denotes a object method that generates other links related to the resource

Marshalling and Unmarshalling

To marshal or unmarshal objects HalMarshaller and HalUnmarshaller will be used:

Marhsalling

HalMarshaller.marshal is used for marshalling. It takes the object, the media type and an OutputStream as input parameters:

Resource r = new Resource( 124L, "John", "1991-03-18");
HalMarshaller.marshal( r, RepresentationFactory.HAL_JSON, System.out);

Unmarshalling

HalUnmarshaller.unmarshal is used for unmarshalling. It takes the object type and an InputStream as input parameters:

Resource r1 = new Resource( 124L, "John Doe", Date.valueOf("1991-03-18"));
        
String representation = HalContext.getNewRepresentation().withBean(r1).toString( RepresentationFactory.HAL_JSON);
                
Resource r2 = null;
InputStream is = new ByteArrayInputStream( representation.getBytes(StandardCharsets.UTF_8));
      
r2 = (Resource) HalUnmarshaller.unmarshal(is, Resource.class);

JAX-RS integration

This libary also provides a content handler, HalContentHandler for JAX-RS based applications. It implements both MessageBodyWriter and MessageBodyReader interfaces. Once is registered as a Provider in the configuration the following code consumes and produces HAL representations transparently:

...
@GET
@Path("/resources/{id}"
@Produces({ RepresentationFactory.HAL_JSON})
public Resource getResource( @PathParam("id") Long id) {
    Resource r = new Resource();
    /* 
        Retrieve resource from database
    */
    return r;
}

@POST
@Path("/resources/{id}"
@Consumes( {RepresentationFactory.HAL_JSON})
public void saveResource( Resource r) {
    /*
        Store resource into database
    */
}