jersey2的错误，求帮忙?报错

@Path("/demo")
public class DemoResource {

@GET
@Produces(MediaType.APPLICATION_JSON)
public ApiResult getUserList(){
ApiResult as = new ApiResult();

System.out.println("abcd");

return new ApiResult();

}

}

访问时报错:

org.glassfish.jersey.message.internal.MessageBodyProviderNotFoundException: MessageBodyWriter not found for media type=application/json

时却什么包吗