javascript - Load One Layer from ArcGIS Server MapServer

I am pretty new to ArcGIS Server and am building a map applications using the Javascript API. I can easily load the map layer below by adding it as a ArcGISDynamicMapServiceLayer

http://www.parkcounty.org/ArcGIS/rest/services/Roads_Map/MapServer/

As you can see there are many layers as part of the above url. What if I just want to load the roads layer as a ArcGISDynamicMapServiceLayer? I've tried replacing the above url with the road specific URL below and that does not seem to work

http://www.parkcounty.org/ArcGIS/rest/services/Roads_Map/MapServer//2

Is there something else I can do as the front end developer or is it up to those that are hosting and managing the server to create a unique url for the roads?

Answer

Make use of the layers property when asking for the exportmap operation from a dynamic map service.

REST API Help on Exportmap operation.

e.g.
This service was published with 3 visible layers. However, can make a request for certain layers.

• show: Only the layers specified in this list will be exported.


• hide: All layers except those specified in this list will be exported.


• include: In addition to the layers exported by default, the layers specified in this list will be exported.


• exclude: The layers exported by default excluding those specified in this list will be exported.

http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Specialty/ESRI_StateCityHighway_USA/MapServer/export?layers=show:2

Also take a look at what additional behaviour you can do with the use of dynamic layers.