javax.ws.rs.client.Entity json() to String

Question

I'm using Jersey to post some entities to a remote REST service through json, here is the client:

Invocation invocation = buildingWebTarget.request(MediaType.APPLICATION_JSON).
                        buildPut(Entity.json(tmpEntity));

at the other side I receive the entity but with all fields set to null. The tmpEntity has no null fields so I'm trying to debug what Entity.json() does, is there a way to print as String the result of Entity.json()??

Using

log.info(Entity.json(tmpEntity).toString())

only returns gibberish.

PS:

My tmpEntity is like:

@XmlRootElement
@Entity
public class City implements Serializable
{

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String name;

    public Long getId()
    {
        return id;
    }

    public void setId(Long id)
    {
        this.id = id;
    }

    public String getName()
    {
        return name;
    }

    public void setName(String name)
    {
        this.name = name;
    }
}