Rendering xml or json data from the controller method is very easy. We have to just follow this syntax.

Example(xml):

    def index
      @users = User.all
       respond_to do |format|
          format.xml {render :xml => @users}
       end
    end


For rails 4 we can also write it like this:

    def index
           @users = User.all
           render :xml => @users
   end

render :xml will automatically call to_xml on the object @users.

But we need a .builder template to display this data i.e index.xml.builder.

Example(json):

    def find_location
       @location = Location.first
       render :json => @location
    end

We generally render data in json format when there is an ajax call like this:

$.ajax({
    type: "GET",
    url: "/find_location",
    dataType: "json",
    success: function(data){
        alert(data.name) 
    }        
});

We can use various template engines like jbuilder,rabl for rendering json response data.